Construction and Building Materials 404 (2023) 133195

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Construction and Building Materials

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Review

An overview of geopolymer composites for stabilization of soft soils

Falk Ayub a, b, *, Suhail Ayoub Khan c
a
Department of Mechanical, Aerospace and Civil Engineering, University of Manchester, Manchester, UK
b
Department of Civil Engineering, Sharda University, Greater Noida, India
c
Department of Chemistry, Jamia Millia Islamia, New Delhi, India

A R T I C L E I N F O A B S T R A C T

Keywords: The efficiency and survivability of any structural component are determined not only by the quality of the
Geopolymer composites building materials used but also by the geological conditions underneath the base of any structure. Soft soils
Soil Stabilization (peat, clay, fine silt, and loose sand deposits)underneath the building structures are frequently the source of
Building material
grave problems such as cracking, sinking, excessive settlement, and so on. It is never recommended to use un­
Curing time
treated soil for engineering purposes. There are myriad techniques and additives (natural or man-made) avail­
UCS
able to enhance the engineering properties of these soils. However, due to impoverished performance, most of
these methods are now redundant. These limitations have resulted in the rise of geopolymer as a feasible
alternative to the conventional techniques of soil stabilization. Geopolymer stabilization occurs through the
creation of a sodium and calcium aluminosilicate gel, which adheres to the neighboring clay particles and so­
lidifies into a thicker, firmer matrix. This review investigates whether the stabilized soil can enhance engineering
properties (strength, durability, permeability, stability, swell-shrinkage assets) and lessen the harmful impacts on
the environment. Moreover, this review will aim to determine whether combining various additives with geo­
polymer can boost soil performance.

1. Introduction reinforcement [6,7]. Chemical stabilization is used to enhance the

properties of soil to boost the geotechnical and engineering performance
Soil stabilization is the technique of convalescing, the behavior of of stabilized soil over unstabilized soil [8,9]. At present, it is a frequently
soils under dynamic forces [1]. It is a fine mode of recuperating the used technique for incorporating binders into the soil to advance particle
geotechnical facets of soft soils. Soft soils that primarily consist of peat, interfacial bonds [10]. Physical and mechanical properties, particularly
clay, fine silt, and loose sand deposits portray low shear strength (<25 shear strength, compressive strength, permeability, and durability are
kPa), bearing capacity, elevated moisture content, compressibility, significant problems for chemically stabilized soils [11,12]. Tradition­
sensitivity, and settlement [2]. These soil types are a blend of diverse ally, chemical treatment involves the application of lime, cement or
minerals like quartz, aluminium silicates, feldspar, carbonates, hy­ their combination [13,14], fly ash [15], rice husk [16], kiln dust [17],
droxides, oxides, and organic materials which furnish these soils the Bitumen [18], recycled materials [19], nanomaterials [20], geo-
capacity to soak up hefty amounts of water resulting in an augmentation synthetics [21], nanocomposites [22]. However, one key issue with
in their volume [2] which make these soils unsuitable for construction these conventional stabilizers (lime, cement) is that their manufacturing
purposes. Due to their elevated compressibility and low strength, processes are energy-intensive and emit a significant amount of CO2
infrastructure built on such soils has the utmost risk of collapsing. As a [23]. The disposal problems of fly ash, rice husk, and kiln dust must also
result, these soils should be modified to ensure pre- and post- be addressed. Furthermore, the agglomeration problem of nano­
construction settlement. materials limits their utilization beyond a certain level. Thus, there is a
In recent history, a variety of soil advancement [3,4] methodologies, dire need for a soil additive with minimal limitations and a greater
classified as mechanical and chemical [4] have been used. Mechanical impact on the properties of soft soils.
stabilization entails reducing the soil’s air voids [5]. The most Soil enhancement with geopolymers has gotten a lot of attention in
commonly utilized mechanical mode to enhance soil deposits is soil the research community, intending to grant a more comprehensive

* Corresponding author.
E-mail addresses: falakayub72@gmail.com (F. Ayub), suhail79chem@gmail.com (S.A. Khan).

https://doi.org/10.1016/j.conbuildmat.2023.133195
Received 1 November 2022; Received in revised form 28 January 2023; Accepted 29 August 2023
Available online 6 September 2023
0950-0618/© 2023 Elsevier Ltd. All rights reserved.
F. Ayub and S.A. Khan Construction and Building Materials 404 (2023) 133195

Fig. 1. Flow chart showing a basic geopolymerization method.

Fig. 2. Molecular Units of Geopolymer.

insight into the expected properties of geopolymer-treated soils, as well { }

as the basic concept dictating the variations in engineering properties Mn − (SiO2 )z − AlO2 n ⋅wH2 O (1)
and pursuance [24]. Davidovits, a French material scientist coined the 2+
Here M is an alkali cation such as K , Ca , or Na that equivalences
+ +
term “geopolymer” which is an inorganic aluminosilicate material the negative charge for Al, n is the degree of polycondensation and z is
created by combining reference materials (precursors) loaded in amor­ the Si/Al molar ratio which usually takes a value of either 1, 2, or 3 [26].
phous silica and alumina with alkali activators. The precursor’s silica However, subsequent research has revealed that z can vary consider­
(SiO4) and alumina (AlO4) undergo polymerization reactions with alkali ably, ranging from < 1 to 300 [27,28]. When z < 1, the blend hardens
poly-silicates, yielding polymeric Si-O-Al bonds with Si and Al in and sets, but encloses crystalline phases along with gibbsite [29]. When
tetrahedral coordination with oxygen [25]. Fig. 1 depicts a cut-down 1 < z < 3, the geopolymer has a three-dimensional, cross-linked un­
geopolymerization process. yielding arrangement with rigid and fragile characteristics and thus
Since the advent of geopolymers, many materials, including fly ash, cementitious and terracotta material; when z > 3, the geopolymer mo­
furnace slag, metakaolin, rice husk ash, kaolinite, and red mud, have lecular structure aims to become two-dimensional, linear, linked with
indeed been researched as promising precursors that can provide adhesive characteristics and when z > 15, the geopolymer illustrates
responsive alumina and silica sources [8]. These alkaline activated rubbery assets [28].
components have been evidenced to be amazing building materials Furthermore, the assets of geopolymers differ considerably based on
owing to their chemical, thermal, and mechanical resistance charac­ the alkali solution concentration, aluminosilicate source, and the cir­
teristics. Over the last century, most geopolymer research has focused on cumstances wherein the geopolymers are polymerized [30,31]. Amongst
developing recyclable and sustainable concrete, with low concentration the other components, the Si/Al molar ratio is known to have a major
paid to soil stabilization. impact [32]. The major enhancement in geopolymer characteristics can
The purpose of this review is to examine the mechanism and impact be attained when the Si/Al molar ratio is between 1 and 3, while the Na/
of geopolymers in the stabilization of soft soil and lessen the harmful Al molar ratio is kept constant at unity [33]. Despite the discrepancy
impacts on the environment. In this cutting-edge analysis, key engi­ caused by a divergence in individual components, geopolymers in a
neering assets such as permeability, stability, and compression strength, broad sense demonstrate several prevalent physical and chemical assets
of stabilized soil are examined. Lastly, the purpose of this analysis is to that are unique from those of other stabilizers. Moreover, geopolymers
determine whether combining various additives with geopolymer can have superior chemical survivability against saline invasion, acid attack,
boost the performance of soft soils. elevated heat and fire, frost intrusion, and sulfate attack due to the
distinctive three-dimensional cross-linked, zeolite-like structure shaped
2. The theory behind geopolymerization by geopolymerization [34].

Geopolymers are created through the amalgamation of alkali- 3. The influence of curing on geopolymerization
activated silicate or hydroxide powder with binders to produce an un­
yielding aluminosilicate substance. The geopolymer reaction process Curing time is critical in the polymerization process for enhancing
was first investigated in 1978 to expand the use of geopolymer as an the capacity of any geopolymer substance. An elevated temperature is
inorganic polymer material for a wide range of industrial applications characteristically used during curing, which aids in inducing kinetic
[23]. Typically, geopolymer structures are described as a succession of acceleration in the geopolymerization procedure [35]. According to
interlocking networks and chains of mineral compounds linked by the Duxson et al. [36]to attain the ideal strength, the curing temperature
effect of covalent bonds [24]. Fig. 2 depicts the molecular units involved and mix design with contaminants should be used to ascertain the
in the geopolymer structure. expansion of geopolymer gel hinges. As per Hardjito and Rangan [37],
Geopolymer chemical reactions were labelled after poly silicates and the curing method significantly aided the initiation of chemical re­
aluminosilicates. The silicate molecular network consists of AlO4 and actions in geopolymer paste, and the strength of geopolymer was greatly
SiO4 connecting via oxygen swap and encloses tetrahedral linking with influenced by the rate and time of curing.
negatively charged particles through the reaction of Al3+ions. In In general, two types of curing processes are used in the formation of
particular, the following empirical formula (Eq. (1)) was used to artic­ geopolymers. These are either dry heat or steam curing. The findings
ulate the reaction of tetra-aluminosilicate. demonstrate that any geopolymer material cured using dry heat gained

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F. Ayub and S.A. Khan Construction and Building Materials 404 (2023) 133195

Fig. 3. Graphical illustration of geopolymerization.

16% more compressive strength than any geopolymer material cured the soil particles and affect the assets of the entrant soil, jointly the
using steam [38]. According to Ahmari et al. [39] in metakaolin-based structure and the mineralogy. The geopolymerization process is divided
stabilization, as the curing temperature rises, more energy is released, into three stages: source alumina and silica cessation, gel formation and
which aids in the dissolution of the alumina and silica found in meta­ readjustment of Si and Al clusters, and polycondensation [36]. This
kaolin particles. It was also stated that to increase the dissolution of process’s reaction mechanism is depicted in Fig. 3.
alumina and silica present in metakaolin, the curing temperature should The chemical reactions that occur during geopolymerization are
be kept between 60 and 90 ◦ C. For every source material, there is a quite complex. It should also be acknowledged that the bulk of the
specific optimum curing temperature to achieve the greatest strength existing geopolymer literature is about “geopolymer concrete” or
response with the geopolymer. “geopolymer mortar.” Because this study targets the interplay among
geopolymers and soils, only key literature is discussed to provide a basic
4. Soil-geopolymer interplay understanding of geopolymerization for the further comprehension of
geopolymer-soil conversations.
4.1. Mechanism Geopolymerization is susceptible to several aspects, including silica
and alumina supply, alkaline concentration, and water content, the
Geopolymers are inorganic polymers with various Si-Al backhaul entire of which can be altered by the existence of soil, particularly when
formations. As a result, the mechanisms by which geopolymers interact the ratio of geopolymer in the geopolymer-soil system is modest. A large
with soil minerals differ significantly from those of organic polymers. concentration of geopolymer for soil treatment might be prohibitively
The primary mechanism for geopolymer stabilization is geo­ expensive. As a result, quality assurance of geopolymerization in the
polymerization. Under alkali conditions, a succession of reactions of geopolymer-soil system may be more challenging than in a sheer geo­
amorphous alumina and silica results in cementitious materials that tie polymer system. Exploring such challenges is critical for gaining a

Fig. 4. Methodology of soil solidification via geopolymers (Copyright from reference [24]).

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F. Ayub and S.A. Khan Construction and Building Materials 404 (2023) 133195

comprehensive understanding of the geopolymer stabilization method­

ologies. Yet, research on this perspective of geopolymer stabilization is
scarce.

5. Geopolymer composites for soil stabilization

Geopolymer potency in soil stabilization is heavily dependent on

both the intrinsic characteristics of the geopolymer components (i.e.,
precursor and inducer) (Fig. 4) and environmental conditions such as
temperature. The configurations and mineral composition of the source
alumina and silica have a significant impact on the geopolymers assets.
In comparison to chain, sheet, and ring structures, framework silicates
have a higher degree of dissociation in alkaline medium and, in general,
better engineering assets after geopolymerization [40]. Several waste
materials or byproducts, such as metakaolin, slag, fly ash, rice husk ash,
silica fume, red mud, and tailing are also regarded as good foundation
resources for geopolymers. Because of the varying concentrations of
amorphous silica and alumina in these materials as a result of high-
temperature smoldering, these by-product materials dissipate effort­
lessly in alkaline solutions [41,42].
In this study, the use of various types of industrial refuse in the
treatment of weak soil with geopolymers is explored. Techniques for
handling and generating a viable stabilizer for geotechnical applications
which is also ecologically friendly are also addressed.

5.1. Volcanic ash based geopolymers

Volcanic ash is a naturally occurring pozzolanic substance composed

of aluminium, silicon- oxides, calcium, and iron that is plentiful in
volcanic areas. The usage of volcanic ash has lately received amplified
Fig. 5. (a) Peak shear strength and moisture content of untreated and treated
attention. It is found in many parts of the world and has numerous innate soil specimens treated with geopolymer and CEM1 with different binder con­
properties that allow it to effortlessly become cementitious. Volcanic ash tents (0 to 15 wt%), curing conditions (Dry Condition, Optimum water Con­
(VA) is shaped in an utterly natural process under high pressure and dition, and Soaked condition), and curing durations of 1 and 28 days; (b) and
temperatures. (c) stress-displacement curves of untreated and treated soil specimens treated
Shariatmadari et al. [43] conducted research on the solidification of with geopolymer and CEM1 with different binder contents and confinements,
soils prone to wind erosion via volcanic ash-based geopolymer. The respectively. All were cured in DC for 28 days (Copyright from reference [50])
study revealed that treating the soil (silty sand soil) with geopolymer can
substantially enhance the threshold friction velocity while decreasing enhanced mechanical properties, and volume stability [48,49].
soil wind erodibility. It was accomplished that proper geopolymer mix Ranjbar et al. [9] investigated the mechanical performance of clayey
design necessitates consideration of soil type, maximum wind speed, soil solidified with volcanic ash-geopolymer and OPC, and the governing
and ambient conditions. components of the solidification procedure, counting curing conditions,
curing time, and binder content. The implementation of both VA and
5.1.1. Volcanic ash (VA) based geopolymer and ordinary Portland cement OPC substitution contents assorted within the relevant range of 0–15 wt
(OPC) % of the soil. Furthermore, the geopolymer stabilization was optimized
The OPC is the most used material in geotechnical engineering by taking the alkali concentration and binder-to-soil ratio into account.
projects due to its adequate availability, mechanical properties, and The study revealed that the soil stabilized with VA-geopolymer resulted
relatively reasonable cost. As a result, it is used in a variety of stabili­ in a 200% increase in compressive strength when compared to the
zation techniques, including deep cement blending, grouting, etc [44]. corresponding OPC samples at the dry curing conditions. Meanwhile,
Conversely, the overreliance on cement has resulted in several ecolog­ OPC-stabilized soil performed admirably at wet curing conditions and
ical concerns, such as high CO2 emissions, natural resource depletion, showed a 33% elevated strength than geopolymer specimens. In another
and waste creation. Moreover, OPC manufacture is a high-energy pro­ investigation, Ghadir et al. [50] examined the notable variables that
cess (5000 MJ/t PC), resulting in CO2 emissions of approximately affect soil stabilization utilizing VA-based geopolymer, such as vertical
0.7–1.1 tons per ton of OPC [45]. Aside from the ecologic disadvantages, confinement, curing condition and time, binder content, and geo­
OPC frequently exhibits high plastic contraction and a decline in me­ polymer mixing parameters like alkali activator content and sodium
chanical characteristics due to water loss and inadequate hydration at hydroxide molarity. The results were also compared to CEM1. A corre­
the initial stage [46]. To minimize the ecological effect and boost me­ lating life cycle assessment (LCA) research on the ecological impacts of
chanical performance, OPC is partially replaced with pozzolanic mate­ the fabrication of two types of binders (i.e., CEM1 and VA-based geo­
rials like volcanic ash (VA), fly ash, red gypsum, etc. Another material polymer) was also carried out. According to this research, the upsurge in
that has been shown to replace 10% of cement without affecting its shear strength was described utilizing changes in cohesion and friction
strength is waste carbon black [47]. Though pozzolanic replacement is of the bulk soil. The overall cohesion force of the treated soil particles
frequently restricted to small quantities, the ecological effect of OPC was shown to be primarily influenced by binder parameters such as
remains a concern. Geopolymers have emerged as a promising alterna­ curing condition, binder content, alkali activator content, and concen­
tive to Portland cement by transforming commercial aluminosilicate- tration (Fig. 5). Moreover, the inclusion of the binder prompted the clay
rich waste into a useful binder. Excluding the ecological implications, particles to aggregate into larger-size clusters, altering the bulk mate­
geopolymer solidified soils have demonstrated enhanced properties to rial’s structure. At the study’s limits, this aggregation enhanced
fulfill the criteria of engineered soft soils via sleek microstructures,

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F. Ayub and S.A. Khan Construction and Building Materials 404 (2023) 133195

Fig. 6. The system boundary under consideration for this LCA (Copyright from reference [50]).

Fig. 7. XRD patterns of the binders, untreated soil and stabilized samples (Copyright from reference [52]).

interparticle friction and was less dependent on binder type and content. repellent, as well as alters soil behavior [51].
In the presence of water, however, the repulsion forces between clay Jahandari et al. [52] carried out the research to thoroughly assess the
particles overcame the chemical bonds and reduced soil cohesion and feasibility of using alkali-activated VA/GGBS in clayey soil stabilization
friction. from various perspectives. The effects of diverse parameters such as the
The LCA outcomes anticipated comparable climate change impacts percentage of VA replaced by GGBS, the liquid/solid ratio (L/S), the
for CEM1 and the VA-based geopolymer employed in this research for curing temperature, and the curing time were researched. Moreover, the
the stabilization of a 1 m3 functional unit of clayey soil with comparable mechanical and durability properties of the stabilized soil were exam­
shear strength. This LCA, on the other hand, was distinct from the re­ ined using compressive strength, freeze–thaw (F-T), and wet-dry (W-D)
port’s boundary conditions (Fig. 6). Irrespective of the boundary con­ durability tests. Furthermore, XRD, FTIR, FESEM, EDS, and elemental
ditions, the activation solution was the key contributor to the mapping were used to investigate the microstructural properties of the
environmental impacts in the geopolymer matrix, which must be stabilized. According to this pilot study, an appropriate amalgamation of
examined further in the advancement of environmentally friendly geo­ VA and GGBS provided ample amounts of calcium, silicon, and
polymer binders for soil stabilization. aluminium, ensuing in the formation of Sodium alumino-silicate hydrate
and calcium aluminate silicate hydrate gels(N-A-S-H and C-(A)-S-H
5.1.2. Volcanic ash and slag (GGBS) based geopolymer gels). The cohabitation of these gels filled the voids in the 3D material
Ground granulated blast-furnace slag (GGBS), is a byproduct of blast- network, culminating in a denser and stronger matrix and, as a result,
furnace iron fabrication. It is primarily composed of silicate and elevated strength values.
aluminosilicate of melted calcium, which must be separated from the It was also found thatthe presence of GGBS lessened the intensity of
blast furnace regularly. It acts as a compaction aid, binder, and water the crystalline phase peaks while escalating the amount of amorphous

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F. Ayub and S.A. Khan Construction and Building Materials 404 (2023) 133195

Fig. 8. FESEM/EDS examination of samples primed with L/S ratio of 0.18 (Copyright from reference [52]).

Fig.9. Simplified diagram of the geopolymerization procedure of samples containing VA and GGBFS binders (Copyright from reference [53]).

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F. Ayub and S.A. Khan Construction and Building Materials 404 (2023) 133195

Fig. 10. Configuration of the best FFBP-neural network, 8–5-10–1 (Copyright

from reference [53]).

phase, according to XRD patterns (Fig. 7). Changing the curing condi­
tion, on the other hand, appears to not affect the crystalline parts of the
geopolymer, confirming that the observed changes in strength values are
due to changes in the amorphous phase. Moreover, the formation of N-
(C)-A-S-H gel in the presence of an appropriate amalgamation of VA and
GGBS was confirmed by FESEM/EDS analysis (Fig. 8), accounting for the
strength development with the initiation of GGBS.
Nader et al. [53] conducted research on using volcanic ash (VA) and
ground granulated blast furnace slag (GGBFS) as raw supplies for geo­
Fig. 11. Permeability coefficients of stabilised soil with KOH a) prior to and b)
polymer cement cured at acoustic and high temperatures (Fig. 9). after soaking (Copyright from reference [56]).
Furthermore, the impacts of VA and GGBFS-based geopolymers on the
geotechnical assets and stabilization of sandy soil were elucidated. The
strength advanced by fly ash-based geopolymer stabilized BCS after 7
study depicted that GGBFS-based geopolymer may be used as a substi­
days of curing was significantly greater than the recommended mini­
tute binder for conventional cement in temperate and clammy regions,
mum strength requirement for sub-base per IRC: SP37 (2012). More­
whereas VA-based geopolymer has immense budding as a green binder
over, the soaked California bearing ratio(CBR) values of NaOH
for soil stabilization in hot and arid regions, which was corroborated by
specimens have been observed to be higher than the un-soaked CBR
pH, unconfined compressive strength (UCS) and electrical conductivity
values, showing strong subgrade stability even under severe climate
(EC) tests. Furthermore, for the estimation of UCS of geopolymerized
situations. In another examination, Murmu et al. [55] employed alkali
sand, two soft computing models were suggested. The evolutionary
activated fly ash geopolymer to enhance the engineering characteristics
polynomial regression (EPR) model was further investigated to establish
of black cotton soil. According to this study, the UCS of stabilized BCS
a framework for multivariable parametric studies as well as a mixture of
enhanced notably, and simultaneously, its swelling and shrinkage
design and optimization strategies beneficial in the QC/QA (Quality
characteristics were diminished which was corroborated by XRD, SEM,
control/Quality assurance) stage of true soil stabilization tasks. On the
and FTIR studies. Alsafi et al [56] utilized low calcium fly ash geo­
contrary, a feed forward back-propagation- Multilayer perceptron
polymer to solidify gypseous soil and lessen collapsibility before wet­
(FFBP-MLP) neural network with an 8-5-10-1 design (Fig. 10) has been
ting. The outcomes of this learning demonstrated that fly ash
discovered to be more precise (root mean square error (RMSE) = 0.0439
geopolymer adhesive had been a stronger stabilizing entity than Port­
kPa, mean absolute error (MAE) = 0.0336 kPa, and coefficient of
land cement because of its calcium-free geopolymer structure. Further­
determination(R2) = 97%) in estimating the UCS of specimens and
more, the research revealed that using potassium hydroxide(KOH, 12 M)
outperformed the best EPR model.
as an activating agent is a better solution in this kind of soil, especially
after the gypsum concentration enhances. Moreover, the initiated fly
5.2. Fly ash based geopolymers ash-treated samples demonstrated a reduction in coefficient of perme­
ability (Fig. 11) and leaching content (Fig. 12). Samples treated with
Fly ash is a granular material created out of the mineral matter in 30% fly ash activated with KOH showed the greatest reduction.
coal, comprising of non-flammable coal matter and a trace of carbon left
over from partial oxidation. Fly ash is beneficial for a variety of building 5.2.1. Fly ash and slag (GGBS)based geopolymer
applications due to its pozzolanic assets. Moreover, it can be employed With fast economic growth, myriad industrial and agricultural
as a stabilizer entity in foundations or highway sub grades. It has also the wastes are being released, posing disposal issues as well as significant
potential to reduce lateral earth pressures via stabilized backfill. In environmental risks. Portland cement manufacturing is one more high-
addition, it can be utilized to enhance embankment slope stability, etc. energy-demanding method that generates more than 4.2 Gt/year of
In recent times, fly ash-based geopolymer has been extensively uti­ greenhouse gases into the atmosphere, accounting for approximately
lized as a substitution for cement and lime to improve soil toughness 12% of total man-made CO2 emissions. Numerous researchers have
while also reducing harmful emissions. Murmu et al. [54] researched to investigated methods to enhance sustainability, ranging from the use of
investigate the viability of utilizing fly ash geopolymer to stabilize black supplementary cementitious materials (e.g., fly ash (FA) and slag) as
cotton soil (BCS). The study demonstrated that even at a small con­ alternatives to ordinary Portland cement (OPC) to the advancement of a
centration (5 M of sodium hydroxide (NaOH) the fly ash-based geo­ new non-OPC binder.
polymer was efficacious for BCS solidification. Furthermore, the Chen et al. [31] optimized the process parameters of fly ash (FA)-

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F. Ayub and S.A. Khan Construction and Building Materials 404 (2023) 133195

Fig. 12. Leaching pace of stabilised soil with KOH a) prior to and b) after soaking (Copyright from reference [56]).

Fig. 13. Impact of the interplay of the two factors on 3 day curing compressive strength (Copyright from reference [31]).

slag-based geopolymer pastes employing response surface methodology Fourier-transform infrared spectroscopy (FT-IR), and field emission
(RSM) and afterward, used this paste as a long-term stabilizer for scanning electron microscopy (FESEM) were used to evaluate differ­
enhancing the mechanical behavior of soft soil in Hangzhou, China. ences in microstructure, chemical information, and mineral phase
Furthermore, the strength escalation rules of stabilized soil were correspondingly.The optimized conditions were 9.988% alkali equiva­
investigated by varying the moisture content (30%-60%), curing age lent, 1.030 geopolymer paste activator modulus, and 0.328 slag
(0–28 days), and geopolymer stabilizer content (8%-14%), and con­ replacement ratio, as well as the global allure of the projected
trasting them to the OPC stabilizer. In addition, X-ray diffraction (XRD), compressive strength values of 3 days (28.10 MPa, Fig. 13) and 28 days

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F. Ayub and S.A. Khan Construction and Building Materials 404 (2023) 133195

Fig. 14. Impact of the interplay of the two factors on 28 day curing compressive strength (Copyright from reference [31]).

Fig.16. Contrasting NF-GMDH-PSO- and ANN-based expected UCS results.

(Copyright from reference [1]).

Furthermore, the escalating trend in strength and quasi-water-cement

through 1/R were linear, and the empirical formula could predict
more than 98% of the deviation. Yaghoubi et al. [34] investigated the
use of fly ash (FA) and slag (S) based geopolymers amplified with six
distinct liquid alkaline activators (L) as a surrogate low carbon viable
material for enhancing the characteristics of soft soils in deep soil mixing
(DSM) implementations. It was revealed that the dosage of L utilized to
activate the precursor (P) had the greatest impact on the creation of
geopolymer gels and, as a result, the strength gain of the stabilized soil.
Sodium-based Ls have been discovered to be more effective than
potassium-based Ls and the fusion of sodium hydroxide and sodium
silicate (NaOH + Na2SiO3) contributed to the greatest gains.Further­
Fig. 15. A general view (a) and a zoomed view (b) of data measured against more, the outcomes of SEM and EDS tests confirmed that calcium (Ca),
predicted values of unconfined compressive strength for all element tests. which is abundant in slag, made a significant contribution to strength
(Copyright from reference [1]). gain than silicon(Si) and aluminium (Al), which are ubiquitous in FA. In
addition, sodium/aluminium(Na/Al) had a more significant influence
(54.69 MPa, Fig. 14). It was revealed that the compressive strength of on strength gain than potassium/aluminium(K/Al). As a whole, an L
stabilized soil increased dramatically with escalating geopolymer con­ consisting of 70% Na2SiO3 with 15% S and 5% FA, and 30% NaOH had
tent, notably from 10% to 12%, due to bonds among the reacted hydrate been recommended as an appropriate geopolymer conjunction to sta­
(including geopolymeric and CSH gel) and soil particles, as well as bilize Coode Island Silt(CIS) in DSM.
thickening and deposition of lamellar and flaky crystals. Moreover, the Javdanian et al. [1] appraised the unconfined compressive strength
rate of variation in strength seemed to be impacted by a slight alter in (UCS) of geopolymer-solidified cohesive soils. Detailed USC findings of
the moisture content of the stabilized soil, with the strength reaching a soils stabilized with blast furnace slag (BFS) fly ash (FA), and their
greatest of 860.26 kPa after 28 curing days with 30% moisture content. configurations were summarized and reviewed. Moreover, a neuro-

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F. Ayub and S.A. Khan Construction and Building Materials 404 (2023) 133195

fuzzy group method of data handling (NF-GMDH) model was created to X-ray powder diffraction (XRD) and cation exchange capacity (CEC)
estimate the USC of stabilized soil samples using the particle-swarm measurements. The study revealed that the alkali content of the ad­
optimization (PSO) algorithm. The study revealed that the envisaged mixtures elevated the pH values of all stabilized soils. Besides, soils
model predicts USC with acceptable accuracy for geopolymer-stabilized stabilized with MKG had relatively elevated CEC, pH, Na+, and lesser
clayey soils [the coefficient of determination (R2) = 0.943, mean abso­ Ca2+ values than samples stabilized with FAG, leading to the soil’s
lute error (MAE) = 0.833, and root mean squared error (RMSE) = greater swelling. Furthermore, the research demonstrated that the CEC
1.512]. It must be remarked that because the majority of the test reports test, in conjunction with XRD mineralogy, can be used to illustrate the
used in this survey had a UCS <10 MPa (Fig. 15), the NF-GMDH-PSO- swelling behavior of soils stabilized with admixtures such as MKG and
based model is more precise in this range (R2 = 0.971, MAE = 0.231, FAG.
RMSE = 0.401). Furthermore, for the prediction of UCS, the advanced
GMDH-based model was contrasted with the artificial neural network 5.2.3. Fly ash and calcium carbide residue (CCR)based geopolymer
(ANN)-based model. The contrast validates the NF-GMDH-PSO model’s Calcium carbide residue (CCR) is a byproduct of the acetylene
pinpoint efficiency in calculating unconfined compressive strength manufacture process via the hydrolysis of calcium carbide (CaC2) and is
(UCS) of geopolymer-stabilized cohesive soils (Fig. 16). Abdullah et al. regarded as a sustainable cementing agent. It is primarily comprised of
[57] in their pioneering work have utilized a blend of fly ash (FA) and calcium hydroxide in the form of slurry [60]. Numerous investigators
ground granulated blast furnace slag (GGBFS) geopolymer to portray the have used CCR to partially or completely swap OPC in concrete appli­
geo-mechanical performance of natural clays utilizing uniaxial and cations [61]. Aside from construction material applications, CCR can be
triaxial testing methodologies. The investigation furnished few signifi­ employed to optimize the engineering assets of problematic soils.
cant findings like the stress–strain response of treated clays was Phummiphan et al. [62] conducted research on the usage of CCR as a
discovered to progress from ductile to post-peak brittle as the geo­ booster in fly ash-based geopolymer to improve the strength properties
polymer content amplified. The increment in geopolymer content pri­ of marginal lateritic soil. According to this pilot study, the 7-day satu­
marily enhanced the yield strength of the clay, resulting in higher rated UCS of marginal lateritic soil-FA geopolymer including and devoid
stiffness. Moreover, the geopolymer treatment improved all of the clay of CCR at various Na2SiO3: NaOH proportions meets the strength re­
soil types dramatically. The tested clays, however, differed significantly quirements for both medium and high-traffic pavement. The NaOH
in terms of peak stress, stiffness, and contraction/dilation tendencies enhances the sustainable UCS of marginal lateritic soil-FA geopolymer,
upon shearing. The primary distinction between the three treated clay and the Na2SiO3: NaOH ratio of 50:50 demonstrates the greatest sus­
types was due to mineralogy, as evidenced by differences in plasticity tainable UCS after 28 days of curing. Phetchuay et al. [63] carried out
and activity indices. Considering that the strength gain is associated the study to investigate the feasibility of employing FA and CCR-based
with the creation of geopolymer gel within treated clay, the configura­ geopolymers as a long-term binder to boost the strength of soft marine
tion changed based on the mineralogical constituents of the soil. Overall, clay{Coode Island Silt (CIS)}.The influencing variables researched
it was concluded that the geo-mechanical performance of geopolymer- encompass water content, curing time, curing temperature, liquid
contemplated clays is associated with clay mineralogy. Singhi et al. alkaline activator content (L), L/FA proportion, fly ash (FA) content as
[49] studied the various mix parameters that influence the strength gain well as CCR content. Furthermore, the carbon footprints of FA and CCR-
mechanism in soil-geopolymer (FA-GGBS based). An effort was also based geopolymer solidified CIS were assessed and contrasted against
made to demonstrate how the unconfined compressive strength of soil- those of cement-solidified CIS at the similar UCS values commonly uti­
geopolymer is governed by Na/Al and Si/Al ratios. The study depicted lized in soil amendment. According to this research, the optimal
that the UCS of stabilized soil increases rapidly as slag content boosts. Na2SiO3/NaOH providing the highest UCS for a given NaOH concen­
The gain in UCS is not noteworthy beneath 8% slag content. While fly tration is governed by L/FA; i.e., a higher FA content (lower L/FA) ne­
ash is employed as a precursor for geopolymer stabilization, the UCS is cessitates a higher NaOH content for leaching silica and alumina; thus,
much lower than when slag-based geopolymer stabilized soil is the optimal Na2SiO3/NaOH declines with FA content. Increased L/FA at
employed. Furthermore, when fly ash and slag are intermingled, due to first enhances the UCS of the FA geopolymer, but when L/FA exceeds the
the differences in dissolution potentials of slag and fly ash, the slag optimal value, the UCS reduces due to precipitation at an early stage
content dominates the blending rather than the Na/Al ratio. before the poly-condensation process in geopolymer. The optimal L/FA
is determined by the initial water content; that is, the optimal L/FA
5.2.2. Fly ash and metakaolin (MK) based geopolymer increases with water content because high water content dilutes the
Metakaolin (MK) is a form of calcined clay that results from the NaOH concentration. According to the findings, the ideal components
calcination of kaolin clay, and it has sparked some intrigue in its giving the highest UCS for w = LL are L/FA = 1 and Na2SiO3/NaOH =
application in the latest days. It is a pozzolanic admixture that is 70:30. Moreover, as the UCS rises, the difference in CO2 footprints be­
extremely reactive. The purity of MK in the chemical makeup may vary tween FA geopolymer stabilized CIS and cement stabilized CIS grows. At
depending on the deposit of the precursor. Lately, metakaolin-based UCS of 400 kPa, 600 kPa, and 800 kPa, FA geopolymer stabilized CIS
geopolymer has been employed to enhance the characteristics of soft emits 22%, 23%, and 43% less CO2-e than cement-stabilized CIS,
soils to reduce their downfalls. Khadka et al. [58] in their pioneering respectively. This demonstrates the value of FA-CCR geopolymer as an
work have treated soil with metakaolin geopolymer (MKG) and fly ash ecofriendly and bold adjunct to Portland cement as a binding agent.
geopolymer (FAG) to evaluate their efficacy in managing volumetric
changes in sulphate soil. MKG and FAG were modified by adding cal­ 5.2.4. Fly ash and polyvinyl alcohol (PVA) based geopolymer
cium hydroxide and calcium sulphate dihydrate (Ca(OH)2 and Polyvinyl alcohol (PVA) is a synthetic polymer that is water soluble.
CaSO4⋅2H2O) in varying weight percentages. After that, altered MKG Its idealized formula is [CH2CH(OH)]n and is manufactured 650,000
and FAG were employed to treat sulphate soil. This study also depicted tons per year for use in construction materials [64]. PVA has been uti­
that to obtain the lowest swell in expansive clay, MKG and FAG can be lized by numerous investigators to improve the strength and durability
optimized based on the Al/Si/Na molar ratio. The optimal Al/Si/Na of recycled waste materials, concrete, and soft soils [65–67].
molar ratio for this study was found to be 1:1.66:1.06. Moreover, it was Suksiripattanapong et al. [68] investigated the feasibility of using
discovered that the concentration of admixtures infused into the geo­ PVA and high calcium FA geopolymer to strengthen soft Bangkok clay
polymer had been in the range of 6.0–9.5% by weight of the geopolymer. (SC) for deep soil mixing (DM) implementations. Besides, the impact of
Mahrous et al. [59] investigated the chemical and mineral performance influence factors on strength development was evaluated. Furthermore,
of high-plasticity soils procured from the Atlanta region in Texas, USA scanning electron microscopy (SEM) of PVA-FA geopolymer stabilized
upon the addition of diverse components of FAG and MKG stabilizers via soft clay was performed to assess the role of influence factors on strength

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F. Ayub and S.A. Khan Construction and Building Materials 404 (2023) 133195

gain. The study depicted that due to a diluted NaOH concentration and content. With escalating moisture content, the optimum single activator
excessive water content, which resulted in many voids, the 7-day and content is amplified. For DS stabilization, a 20% optimum SH-GGBS (SH
28-day UCS values reduced as the water content increased. The opti­ is sodium hydroxide) or SS-GGBS (SS is sodium silicate) binder can be
mum constituent for FA geopolymer stabilized SC specimens in terms of substituted for 15% PC. Furthermore, the mass ratio of composite acti­
workability and the cost was found to be at 1.0 liquid limit (LL), vators (H/S) had a significant impact on the strength development of
Na2SiO3/NaOH = 1, FA = 40%, and L/FA = 0.6. The strength require­ HSGDS (SH-activated GGBS stabilized DS). The HSGDS UCS amplified
ment was fulfilled by its 28-day UCS of 1026 kPa. PVA can form strong with H/S ratio until it reached an optimum value and then declined. At
links with soil particles, resulting in an increase in UCS as PVA con­ water contents of 60, 70, and 80%, the optimum H/S for HSGDS was
centration and PVA content are enhanced to optimal levels. The UCS determined to be 2/3, 2/3, and 1/4, respectively. In general, the opti­
decreased above the optimum PVA concentration and content because mum UCS of HSGDS was higher than that of PC stabilized DS (PCDS)
the PVA films slowed the geopolymerization reaction. PVA improved the with the corresponding PC. By correlating the optimum UCS within the
7-day and 28-day UCS values by 40% and 42%, respectively, when same activator dosage, composite activators were discovered to be more
compared to the control specimen. efficient than single activators in initiating GGBS for increased stabilized
DS strength. The unconfined compressive strength (UCS) values ob­
5.3. Ground granulated blast furnace slag (GGBS) based geopolymers tained from GGBS-based geopolymer stabilized clayey soils and
modelled using two soft computing approaches, neural network-based
The development and implementation of non-traditional stabilizers group data handling method (GMDH-NN) and artificial neural net­
have the potential to minimize the usage of OPC in soil stabilization, works (ANN) was examined by Eidgahee et al. [74]. Furthermore,
thereby lowering costs and adverse environmental effects. GGBS is a optimized neural network architecture and an empirical equation for
readily available material, and its usage will help to alleviate environ­ predicting the potency of fine-grained soil stabilized with GGBS-based
mental issues such as waste disposal [69]. Alkali activation of GGBS geopolymer were envisioned. According to the study, the developed
should be investigated further to maximize its use as an alternative to model was most appropriate for soils with physical characteristics that
OPC. were similar to the soil samples used in the current study. Moreover, the
Thomas et al. [70] carried out the research to investigate the per­ findings demonstrate that the ANN coefficient of correlation (R) for both
formance of soil stabilized with alkali-activated GGBS and enzymes. The testing and training datasets was higher than the GMDH-NN coefficient.
study revealed that the enhanced stabilizer dosage reduced maximum Based on R values of 0.98 and 0.99 for training and 0.96 and 0.97 for
dry density(MDD) while increasing optimum moisture content (OMC), testing GMDH-NN and ANN models, respectively, the effectiveness of
unconfined compressive strength (UCS), and shear strength parameters these two techniques for anticipating unseen data was allowable.
(cohesion and angle of internal friction). The UCS and shear strength Overall, it was found that using the GMDH-NN method yields a simple
parameters of alkali-activated GGBS (20%)-stabilized soil outperformed equation. The ANN outcome was more accurate, but only the optimized
those of OPC-stabilized soil (12%). The curing time of 28 days has a network can be shown. Noolu et al. [75] carried out the research to
noteworthy effect on UCS. Moreover, the UCS of alkali-activated GGBS- study the impact of GGBS concentration and NaOH molarity on the
stabilized soil was 1.15 times higher than that of OPC-stabilized soil and resilience and strength assets of geopolymer stabilized black cotton soil.
5.5 times greater than that of bio-enzyme-stabilized soil. On the whole, The study revealed that the exploit of GGBS for stabilization purposes
it was concluded that in comparison to an enzyme, alkali activated GGBS led to a substantial advancement in the strength properties of black
was more efficient in generating strength in the chosen soil. Jiang et al. cotton soil (BC), as evidenced by the unconfined compressive strength
[71] examined the longevity of a road subgrade fill soil stabilized with test results. When compared to innate soil, GGBS stabilization increased
lightweight alkali activated GGBS (LAS). In this research, LAS stabilized unconfined compressive strength by 5.2 times. Furthermore, the un­
soil was immersed in a concentrated Na2SO4 solution before being confined compressive strength increased dramatically up to 8 M NaOH
measured for mass change, unconfined compressive strength, and solution. Additional inclusion caused a loss of strength. The durability
thermogravimetric characteristics. It was found that with escalating findings acquired with GGBS-based geopolymers demonstrated a 10%
immersion time, the LAS solidified soil accomplished a reluctant and strength reduction after 12 wetting and drying cycles. In general, it was
reliable drop-in UCS from 750 to 800 kPa to 540–700 kPa. This is due to accomplished that alkali activated GGBS has the potential to enhance
the joint effect of ettringite, thaumasite, and gypsum formation, as well the engineering performance of BC.
as the occurrence of larger empty spaces in LAS. The preliminary 28 days
of immersion in the Na2SO4 solution led to a rise in UCS, but subsequent 5.3.1. Ground granulated blast furnace slag (GGFS) and basic oxygen
immersion resulted in a sharp loss of strength. The mechanical, physical, furnace slag (BOFS) based geopolymer
and hydraulic properties of lightweight geopolymer stabilized soil BOFS is a significant waste product produced during the production
(LGSS) and its correlation to lightweight cement-stabilized soil (LCSS) of steel. The application of BOF slag as a road ballast and land filler has a
were investigated by Duet al. [72]. The study furnished few significant long record in most industrialized countries [76]. Besides, it is known to
findings at the same curing time and, the density of the UCS of LGSS was have strong surface properties, tough alkalinity, affluent angularity as
2–3.5 times that of LCSS. Moreover, the LGSS (12.68%) has an elevated well as reasonably superior mechanical properties characteristics [77].
calcium silicate hydrate(C-S-H) content than the LCSS (6.8%). The Salimi et al. [78] examined the physicochemical characteristics as well
volumetric absorption(VA) and hydraulic conductivity (k) values of as the mechanical performance of kaolinite clay stabilized with GBFS-
LGSS were discovered to be associated with the volume of enlarged air and BOFS using a battery of tests that included Electrical Conductivity
pores (>10 μm), owing to the overreliance of VA and k on the volume of (EC), pH, UCS, and one-dimensional consolidation with X-ray diffraction
interconnected enlarged pores; the UCS of LGSS was discovered to be (XRD) and scanning electron microscope (SEM) analysis. The perfor­
greater than that of LCSS, owing to more hydration products that occupy mance of lime and magnesium oxide as promoters on clay-slag based
the voids of soil, as corroborated by the fact that more C-S-H was found geopolymer was then evaluated by incorporating alkaline solutions into
in the LGSS than in the LCSS from the thermo-gravimetric analysis the optimum blends. According to the study, the inclusion of all of the
(TGA). Lang et al. [73] carried out research to create an alkali-activated researched stabilizers (up to 20%), has a minor effect on the UCS of clay
GGBS binder that can be used instead of Portland cement (PC) to sta­ samples at 20 ◦ C, and the curing time has no discernible impact on the
bilize dredged sludge(DS) with varying moisture contents. The investi­ strength. conversely, raising the temperature from 20 to 45 ◦ C can result
gation revealed that the strength gain of stabilized DS was significantly in faster cementitious product formation, particularly in MgO-BOFS
influenced by the single activator type and dosage. The UCS of stabilized (MB) and CaO-BOFS (CB) samples, with the UCS value of these two
DS augmented initially and then declined with the single activator samples at 20% content after 90 days of curing reaching 4 and 4.7 MPa,

11
F. Ayub and S.A. Khan Construction and Building Materials 404 (2023) 133195

Fig. 17. SEM and EDS micrographs of geopolymer-enhanced soil. (Copyright from reference [88]).

respectively. Moreover, when contrasted to the MgO-GBFS (MG) and generate electricity. Rice husk’s high silica content, combined with its
CaO-GBFS (CG) treatments, the MB and CB-treated samples have an harsh, thick, and stiff nature, makes disposal incredibly challenging
advantageous pH value and better compressibility. The amplified [79]. As a result of increasing environmental concerns and the need for
pozzolanic activity in the former compositions, as confirmed by the XRD renewable energy, the combustion of rice husk for electricity generation
patterns and SEM analyses, can explain these findings. at zero net carbon output to the atmosphere is a beneficial and cost-
effective resolution [80]. RHA is the residue left after incinerating rice
husk, and its major composition is amorphous silica, which varies
5.4. Rice husk ash (RHA) based geopolymers depending on the process of combustion. Because of its high amorphous
silica content, RHA has been efficaciously utilized as a pozzolanic ma­
Rice husk ash (RHA), a non-conventional agro-waste material as well terial in concrete as well as in soil to improve its durability and lessen
as industrial waste, is generated by the burning of rice husk in order to

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F. Ayub and S.A. Khan Construction and Building Materials 404 (2023) 133195

permeability, etc [81,82]. stabilised soil. Shrinkage strain reduction in chemically stabilized
Khanday et al. [79] investigated the stabilization of peat (sapric, pavement sub layers is advantageous for lessening shrinkage-induced
fibric, hemic)by employing RHA-based geopolymer. The performance of cracks in pavements. Overall, shrinkage declined as MKG concentra­
RHA-based geopolymer stabilized peat was evaluated using pH, UCS, tion amplified. The long-term advantages of the metakaolin-based geo­
EC, EDX, FESEM, and XRD analysis. This study furnished a few signifi­ polymer to effectively cure a high plasticity expansive clayey soil and its
cant findings, the UCS elevated with the alkali/binder(A/B) ratio until it correlation with lime treatment were investigated by Samuel et al. [86]
reached 0.7 and then began to fall. Furthermore, the highest UCS was and the long-term advantages were assessed using the sustainability
acquired for all peats at 20% binder content by weight of dry peat. The framework developed at University of Texas at Arlington, which em­
reduced binder content doesn’t quite produce enough geopolymer to ploys a weighted multi-criteria evaluation based on resource consump­
bind the soil particles, even though a portion of the larger RHA persists tion, environmental impact, and socioeconomic impact. According to
unreacted. Furthermore, the micrographs depicted that the voids were this study, the incarnated energy and global warming potency of pro­
clogged by cementitious geopolymerization products, resulting in a ducing a kg of lime have been discovered to be significantly greater than
closely packed and smooth peat-geopolymer lattice. This has been metakaolin, the main ingredient of the geopolymer. Based on the pro­
validated by XRD analysis. As a result, the usage of RHA-based geo­ portion used, along with presumptions about cost and transportation, a
polymer to stabilize peat not only has proven to be more ecologically metakaolin-based geopolymer with a lesser sustainability index(ISus)
sound than conventional binders but also a better alternative as a was discovered to be a more viable alternative to conventional lime
pozzolanic material for peat stabilization. Swamy et al. [83] studied the treatment for soil stabilization. Luo et al. [87]examined the viability of
stabilization of laterite soil with a geopolymer based on rice husk ash using geopolymer as a new option for silty clay foundation treatment.
and the efficiency of the stabilizer in boosting the strength of the UCS, SEM, and X-ray energy dispersive spectroscopy (EDS) was per­
preferred soil. Besides the impacts of rice husk ash, geopolymer, and rice formed on silty clay stabilized by metakaolin-based geopolymer (MKG).
husk ash-based geopolymer were investigated. The study depicted that Furthermore, the effects of metakaolin content, modulus, and alkali
the inclusion of RHA, geopolymer, and RHA-based geopolymer in soil activator concentration on the mechanical behavior of geopolymer
improves its toughness. Moreover, when contrasted with RHA and stabilized soil were described. The study revealed that the MKG has a
geopolymer alone, RHA-based geopolymer was a very appropriate sta­ clear impact on increasing soil UCS, and its mechanical properties such
bilizer. With a 7-day curing period and 25% geopolymer content, the as Young’s modulus, and failure strain were also improved when con­
strength of the soil was enhanced twofold when contrasted to unstabi­ trasted to samples stabilized with lime and ordinary Portland cement.
lized soil. Finally, it was concluded that RHA-based geopolymer stabi­ SEM analysis confirmed the presence of cementitious materials in the
lization can be applied efficaciously for subgrade stabilization, resulting stabilized soil sample, with the soil exhibiting a more coherent and
in environmentally sustainable pavements. stiffer microstructure after MKG treatment. Furthermore, it is difficult to
cause salt swelling damage using EDS analysis when there are no large
5.4.1. Rice husk ash (RHA) and fly ash (FA) based geopolymer amounts of calcium ions in the sample. Overall, this study confirmed
The stabilization of black cotton soil (BCS) via geopolymer based on that MKG can serve as a potent entity for silty soil stabilization. Wang
fly ash and rice husk ash (FARHA) was examined by Murmu et al. [84]. et al. [88] investigated the strength behavior and material proportion of
Moreover, the stabilizing ability of geopolymer via UCS, shrinkage, and the metakaolin-based geopolymer-enhanced clay soil, where the alkali-
free swell ratio (FSR) test was detailed. The study revealed that the activator was a powdered amalgam of NaHCO3 and CaO. Moreover, the
FARHA geopolymer-stabilized BCS was less susceptible to varying water strength behavior and stabilization effect of the geopolymer-enhanced
content, as evidenced by smaller FSR and shrinkage values. As a result, clay were thoroughly assessed in comparison to lime soil, cement soil,
stabilized BCS was a more stable material than raw BCS. Moreover, and pure clay soil. The study revealed that the geopolymer-enhanced
within 7 days of curing, the stabilized BCS gained strength of more than soil performed better in terms of shear strength, tensile strength, and
1500 kPa; hence, FARHA-stabilized BCS can be employed for applica­ UCS. SEM with EDS (Fig. 17) analysis revealed that the geo­
tions requiring increased strength in a brief amount of time. As a result, polymerization of the geopolymer binders advances as the curing time
mixed ash geopolymer can be employed to stabilize BCS in instances progresses. The aluminosilicate gels formed by the geopolymerization of
requiring rapid strength development as well as being efficient in the geopolymer binders enhanced interaction among the flaky units of
reducing swelling and shrinkage characteristics. pure clay transitioning into cementitious links, and the framework of the
geopolymer-enhanced soils was denser than the configuration of OPC
5.5. Metakaolin (MK) based geopolymers soil. Hanegbi et al. [89]looked at the utilization of a metakaolin-based
geopolymer with various compounds and levels for reinforcing the
Metakaolin was discovered to be a top-quality material all over the topsoil of semi-arid loess. The study depicted that the clay-based geo­
world. It was largely employed as a precursor in the geopolymer pro­ polymer examined in this research demonstrated a strong ability to be
duction process, alongside fly ash and GGBS. It is a white powder with employed as a dust suppression agent and soil stabilizer in loess soils. In
particles smaller than 2 nm in diameter, making it finer than OPC. contrast to basic items (PVA, brine, bitumen), the usage of the geo­
Moreover, MKG has proved to be the best admixture in reducing the rate polymer for dust suppression resulted in no dust production. Moreover,
of soil swelling than GGBS [85]. the geopolymer examined in this study performed admirably well in the
Zhang et al. [48] examined the viability of metakaolin based geo­ tensile test as a soil stabilizer. As, a whole, it was determined that there
polymer (MKG) as a soil stabilizer via Young’s Modulus (E), UCS, failure is a high scope for improving natural soil stabilizers from mineral
strain (ef), and volumetric shrinkage strain during the curing age. sources that outperform existing synthetic stabilizers. The effect of ba­
Moreover, a one-way analysis of variance (ANOVA) was conducted to sicity on a metakaolin-based polymer binder to strengthen clay was
investigate the statistical pattern of mechanical characteristics relying investigated by Shi et al. [90]. Moreover, the influence of alkali activator
on curing age and geopolymer levels. The study depicted that when the molar concentration, MKG concentration, and curing time on UCS was
MKG concentration was greater than 11%, the UCS values of stabilized investigated. The study revealed that the UCS of clay improved with the
soils were significantly greater than raw soil and greater than 5% PC rise in MKG, reaching 4109 KN when the MKG content was 12%. SEM
(Portland cement) stabilized soil. Besides, MKG-stabilized soil samples revealed that the treated soil had a compact matrix, and the clay par­
were less fragile than unstabilized equivalents, which is useful for the ticles were coated with gelling products formed by the geopolymer,
efficiency of flexible pavement. Furthermore, when the concentration of which added to its strength.
MKG was greater than 8%, the shrinkage strains of MKG-stabilised soil
were significantly smaller than those of unstabilized soil and 5% PC-

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F. Ayub and S.A. Khan Construction and Building Materials 404 (2023) 133195

5.5.1. Metakaolin (MK)and fiber-reinforced geopolymer 5.7. Copper slag (CS) based geopolymers
When chemically stabilized soil is subjected to stresses, the incor­
poration of fibers is an efficacious method for enhancing ductility and Copper slag is a byproduct of copper smelting and refining that is
fracture toughness and minimizing the expansion of microcracks [91]. classified as non-hazardous by the US EPA and the Basel Convention. It
Wang et al. [92]explored the chemical fabrication and mechanical is a dark black powder with high silica and alumina content that can be
characteristics of metakaolin-based geopolymer-stabilized clay soil used as a precursor for a geopolymer base.
(GSCS). Besides, basalt fiber (BF) was employed to boost the mechanical Fakhrabadi et al. [95] examined the impact of a CS-based geo­
behavior and cracking resistance of GSCS because it is a low-cost inert polymer on the Microstructural and mechanical assets of clayey-sand
fiber with high reliability, tensile strength, and deterioration resistance against wetting–drying (W-D) cycles. According, to the study, CS-
in alkaline surroundings. Furthermore, the toughening methodology based geopolymer drastically enhanced the clayey-sand, which was
and strength behavior of GSCS reinforced with BF (FRGSCS) were unsuitable for weathering conditions. UCS tests after W-D cycles show a
thoroughly discussed. The study revealed that the outcomes of significant decline after the second cycle for samples containing 10%
comparative tests showed that FRGSCS outperformed the other four and 15% copper slag. However, the effects of W-D cycles on strength
types of soils in terms of strength performance. In an alkali surrounding, were greater in samples with higher elasticity in samples with 15% CS
the products of alkali-activated binders (AAB) fill the original pores than in samples with 10% CS. In accordance with the microstructure
between soil particles, making clay soil (CS) more compressed and outcomes, the most crucial proportions for the geopolymerization pro­
consolidated. The inclusion of BF improves the reliability of GSCS, cess are Si/Al, NA/Al, and Ca/Si. Furthermore, as the number of W-D
allowing it to slow down the increase of destruction and deflection. cycles increased, so did the number of fractures and cavities. Finally, it
Moreover, the fiber–matrix interactions, such as crack deflection, was concluded that the clayey-sand stabilization with CS-based geo­
bridging effect, branching effect, and interface bond, can illustrate the polymer is an adequate and long-lasting technique for geotechnical
impact of BF on the toughening methodologies of GSCS. The signifi­ assessment in harsh climates.
cantly improved mechanical properties of soil geopolymer-fibre com­
posites are attributed to fiber–matrix interactions. 5.8. Palm oil fuel ash (POFA) based geopolymers

5.6. Red mud (RM) based geopolymers Palm oil fuel ash (POFA) is a byproduct obtained from the burning
residues of palm oil (PO) trees in the palm industry. POFA is classified as
Red mud (bauxite residue) is a by-product of Bayer’s aluminium an environmentally hazardous waste. The massive growth in PO yield in
production process. It was calculated that approximately 5 tons of red tropical states has resulted in an accumulation of POFA and a significant
mud are generated as a by-product during the manufacture of 1 ton of ecological load. To tackle this issue, POFA has been employed to sta­
aluminium. Red mud is identified as an alkaline material in nature bilize soft soils owing to substantial differences in particle size, and
because it is composed of an excess of metallic ions and minerals that are pozzolanic activity.
considered harmful to the environment. Khasib et al. [96] studied the efficacy of POFA-based geopolymer in
Chandra et al. [93] explored the viability of a geopolymer composite clayey soil solidification. Moreover, the mechanical behavior of two
produced from RM and FA as a durable subgrade material for road varieties of clayey soil prior to and after treatment with POFA-based
construction. CBR and UCS tests were used to assess the strength growth geopolymer was assessed using UCS and direct shear tests (DST). The
of different combinations. Besides, SEM, XRD, and FTIR were used to study revealed that POFA-based geopolymer-treated clayey soil samples
investigate the mechanism of strength enhancement. According to this have relatively higher MDD (maximum dry density) values than un­
study, the inclusion of FA and alkaline activators in RM improved the treated specimens, with a decline in the associated OMC (optimum
strength parameters significantly, which was corroborated by Micro­ moisture content) as the geopolymer potency increases, indicating
structural analysis. Since FA contains low-density particles, a 20% FA to advancement. Moreover, The UCS data confirmed that the geopolymer
RM replacement was proposed as the optimal combination, with further mix with the highest POFA percentage (G40PA) achieved the highest
increases in FA resulting in a reduction in MDD (maximum dry density). strength at both curing times. The effect of POFA-based geopolymer was
Most of the alkaline activated specimens achieved a CBR value of 8, more visible at 28 days due to the growth of increased strength in
which was double that of raw RM, demonstrating the material’s viability comparison to 7 days of curing. Furthermore, even without curing, the
as a subgrade material as per IRC guidelines. Moreover, the increment in addition of POFA-based geopolymer improved shear strength parame­
curing time resulted in a significant boost in strength, which is a ters, particularly soil cohesion. Sukmak et al. [97] studied the strength
distinctive feature of geopolymerization. Alam et al. [94] investigated and microstructure of a geopolymer stabilized soft soil (SS) containing
the impact of Na2SiO3 activation on the durability, strength, and palm oil fuel ash (POFA) as a source material. In this study, the optimal
microstructural properties of GGBS melded red mud on its potential use Na2SiO3: NaOH ratio, POFA: SS proportion, and liquid alkaline activator
as a geotechnical material. Besides, the current study looked at the (L) content for POFA-SS geopolymer in subgrade uses were also
chemical analysis of leachate in terms of water-leachable heavy toxic explored. The exploration furnished a few significant findings like lower
metals as recognized by the environmental protection agency (EPA). The POFA: SS ratios necessitated more NaOH and L absorption by both the
study revealed that the UCS of NALCO red mud (NRM) was 564.08 kPa internal and external negative layer interfaces of the SS in order to
with sudden failure (residual strain = 0.1%), whereas the UCS of HIN­ establish the stabilized soil structure. As a result, for POFA: SS = 30:70,
DALCO red mud (HRM) was 441.45 kPa (the residual strain of 0.35%). 40:60, and 50:50, the optimum Na2SiO3: NaOH ratio and L content
The stabilization with GGBS enhanced the UCS as its concentration providing the highest strength were 40:60, and the optimum liquid
raised for both the red mud (NRM and HRM) but wasn’t reliable under alkaline activator content or OLC (22.8%), 50:50 and 1.2OLC (L =
alternate wet-dry cycle conditions. After 12 wet-dry cycles, the alkali 31.4%), and 60:40 and 1.4OLC (L = 44.55%), respectively. Moreover,
activated GGBS stabilized red mud was found to be more reliable and the cementitious products were highest in the samples with the highest
had greater compressive strength than samples cured under ambient UCS. The most common cementitious product found was gismo-dine (C-
conditions. Furthermore, apart from Hg, the harmful heavy metals (Cr, A-S-H and C-(N)-A-S-H).
As, and Pb) recognized by the EPA for toxicity properties were observed
to rise after stabilization but remained within acceptable limits. 5.8.1. Palm oil fuel ash (POFA) and glass fiber-reinforced geopolymer
Glass fiber is a substance composed of fine glass fibers. The material
is considered one of the most dynamic industrial materials available
today. Its mechanical properties are comparable to those of other fibers.

14
F. Ayub and S.A. Khan Construction and Building Materials 404 (2023) 133195

Fig. 18. Experiments encapsulated in this literary work.

Several polymer products use glass fiber as a reinforcing agent to create were discovered to be appropriate for engineering earthworks after 28
a very robust and light material. Moreover, when relatively high tensile and 90 days of curing time. In another investigation, Baldovino et al.
strength fibers are incorporated in a soil matrix, shear stress is produced [100] explored the improvement of the split tensile strength (qt) and
between the soil particles, which is then conveyed to the fibers as tensile reliability against wet-dry cycles of compacted soil–cement mixes by
strength, boosting soil strength, and accelerating the brittle-to-ductile introducing recycled glass powder (GP) in three weight percentages: 5%,
post-peak behavior transition. 15%, and 30%. The study depicted that, adding GP to cemented silty soil
Abdeldjouad et al. [98] focused on the discovery of a novel alkali- was an effective way to avoid dumping this trash in landfills. Because of
activated binder for soil stabilization via previously invented POFA the significant amount of silica and the advancement of geopolymers,
and potassium-based activators. Another aspect of this research was the GP could be employed in ground improvement, lessening the amount of
significance of glass fibers, which were implemented into the blend as a cement, etc. Besides, by enhancing the curing time from 7 to 90 days and
source of distinct reinforcement. Besides, the mechanical performance introducing three proportions of GP, the split tensile strength of
was assessed using two tests that allowed for the determination of soil–cement has been enhanced. Split tensile strength is affected by the
compressive strength (uniaxial compression tests) and tensile strength porosity/cement index and rises with escalating GP content. Bilondi
(indirect tensile and flexural tests). According to the study, when POFA et al. [101] conducted research to study the potential use of a recycled
was employed as a source binder and potassium hydroxide was utilized glass powder or RGP-based geopolymer as a soil stabilizer. The study
as an activator in the alkaline activation process, the compressive revealed that compared to the unstabilized sample; the UCS and failure
strength of medium plasticity sandy clay was enhanced from brittle. strain (εf) values of all geopolymer-stabilized samples were enhanced.
Moreover, when 3 to 5% glass fibers were added to the alkali-activated Furthermore, increasing the RGP content to the optimum value (15%)
soil amended with POFA, the peak tensile strength of the soil increased. enhanced the UCS and failure strain (εf) of the samples. The UCS values
Furthermore, the addition of glass fibers to the alkali-activated soil were augmented as the curing time of stabilized samples enhanced. The
amended with POFA changed the soil matrix’s post-peak behavior from UCS value samples were maximum after 91 days of curing, however, the
brittle to ductile. The Microstructural analysis revealed that the inter­ rise in strength after 28 days was not important. Thus, the findings of the
play between the glass fiber surface and the alkali-activated matrix tests revealed that a rich silica source, like glass powder, was required
attributed to the reinforced soil’s improved behavior. for improved soil stabilization and the formation of a geopolymer gel.

5.9. Waste glass powder (GP) based geopolymers 5.10. Nanomaterials (nanoclay and nano silica) and Taftan pozzolan
(TP) based geopolymers
The glass powder is an inert material derived from the separation of
municipal solid waste. In a broad sense, the glass waste gathered is a With the advancement of nanotechnology, nanomaterials have
non-biodegradable matter with elevated amorphous silica content. It become more prevalent in geopolymers. However, research on the ef­
improves the mechanical properties of stabilized soil by optimizing the fects of nanomaterials on geopolymer characteristics in soil stabilization
gel matrix and soil microstructure with unreacted alkali particles. In the is limited. Shokatabad et al. [102] explored the usage of Taftan pozzolan
context of long-term stabilization, encouraging the exploit of recycled (an eco-friendly material), and nanomaterials to stabilize weak soils.
glass waste in powder form can reduce energy usage and enable resource Moreover, parameters influencing the compressive strength of the sta­
conservation. bilized soil were explored and assessed, including curing time, amount
Baldovino et al. [99] thoroughly investigated the use of glass residue of nanomaterials, and amount of alkaline solution and application. Ac­
as a geopolymerization precursor in lime-soil compacted mixes for cording to the study, natural pozzolans and nanomaterials were excel­
earthwork applications. The study revealed that the porosity-binder lent stabilizers for sandy soils and increased compressive strength
index was the primary factor that governed the strength, accumulated dramatically. The optimal quantity of nanomaterial (2%) was required
loss of mass (ALM), and microstructure development of silt-GP-lime for appropriate geopolymerization and improved mechanical behavior
compressed mixes. The splitting tensile strength (qt) and UCS (qu) of stabilized soils.
were both enhanced by incorporating glass powder (GP) and intensi­
fying the curing time. Moreover, ALM declined as a result of the 6. The effect of precursors on soil morphology
enhanced microstructure with closely packed matrices induced by sili­
con dissociation in the GP particles. Furthermore, it produced different One of the primary goals of any geotechnical project is to increase
silt-lime mixes suitable for sub-base implementations in pavements with soil’s shear strength [103]. Typically, shear strength is estimated using
a minimum qu value of 1.2 MPa and maximum ALM values of 7–8% the mechanical characteristics of the soil. Soil particles are entirely or
(American standards) and 14%(Brazilian standards), GP was a sustain­ partially reorganized as a result of a variety of external forces. In such
able binder for soil stabilization. After 7 days of curing time, neither of cases, the soils fail to endure or transmit the load, resulting in structural
the analyzed mixes met the specifications for qu, but 7 out of 9 mixes failure. The completeness of the reaction is also determined by its

15
F. Ayub and S.A. Khan Construction and Building Materials 404 (2023) 133195

Table 1 Table 1 (continued )

Soil stabilisation employing geopolymers. Geopolymer Alkali Alkali UCS or curing Ref
Geopolymer Alkali Alkali UCS or curing Ref precursor and type activator binder compressive time
precursor and type activator binder compressive time of Soil ratio strength of
of Soil ratio strength of treated soil
treated soil (MPa)
(MPa)
MKG/Fiber with Na2SiO3 0.5 0.93 7 days [92]
VA with silty sand NaOH + – 2.00 28 [43] clay soil + CaO
Na2SiO3 days RM/FA with silt NaOH + – 2.7 28 [93]
VA with clayey NaOH – 12.00 28 [9] Na2SiO3 days
soil (plastic soil) days Copper slag with NaOH + 1 0.67 14 [95]
VA in cement NaOH – 12.00 28 [50] clayey-sandy Na2SiO3 days
stabilized soil days soil
VA/GGBS in NaOH 0.22 3.14 28 [52] POFA in Clayey NaOH + 1.32 4.18 28 [96]
clayey soil days soil Na2SiO3 days
VA/GGBS in NaOH + 3.0 6.21 28 [53] POFA with soft NaOH + 1.2–1.4 0.29 7 days [97]
sandy soils Na2SiO3 days soil Na2SiO3
FA with black NaOH + – 2.70 90 [54] POFA/glass fibers KOH – 5.7 28 [98]
cotton soil Na2SiO3 days with sandy clay days
FA with expensive NaOH + – 2.50 28 [55] Glass powder (GP) CaO + – 1.2 7 days [99]
clay Na2SiO3 days with silty soil MgO
FA in gypseous NaOH + 2.0 29.3 90 [56] Recycled glass NaOH – 2.5 7 days [101]
soil KOH days powder in
FA/Slag with soft NaOH + 0.32 0.86 28 [31] clayey soil
soil in Na2SiO3 days Nanomaterials NaOH 0.45 7.96 and 5.96 90 [102]
Hangzhou, (nanosilica and days
China nanoclay) and
FA/Slag in Coode NaOH + – 8.50 28 [34] Taftan pozzolan
Island silt Na2SiO3 days with sandy soil
FA/Slag in NaOH 0.85 24.26 28 [1]
cohesive soils days
FA/Slag with clay NaOH + 0.4 0.4 28 [57] microstructural analysis in any technique of stabilization [24]. Each
soils Na2SiO3 days stabilization substance mentioned in this review optimized the soil’s
2
FA/Slag with NaOH + 0.65 11.3 N/mm 28 [49]
microstructure by creating a constrained bonding effect. The character
clayey soils Na2SiO3 days
FA/MK with NaOH + – – – [58] of the binder material, curing temperature, time, and alkaline solution
highly Na2SiO3 concentration all contributed to the development of microstructure in
expensive soils any soil. The microstructural assets of the soil stabilized with the
FA/MK with high NaOH + – – – [59] different geopolymer pastes were also discussed in the literature
plasticity soils Na2SiO3
FA/CCR in NaOH + 9.20 28 [62]
reviewed in this paper.
lateritic soil Na2SiO3 days When contrasted with traditional cement stabilization, geopolymer-
FA/CCR with soft NaOH + 0.8 28 [63] based stabilization furnished a harder and tougher soil microstructure
marine clay Na2SiO3 days owing to the existence of a cross-link structure. When contrasted with
FA/PVA in soft NaOH + 0.6 1.02 28 [68]
the cement matrix of C-A-S-H gel, the advancement of C-A-S-H gel with
Bangkok clay Na2SiO3 days
GGBS in Tilda soil NaOH – 0.69 28 [70] an extended matrix was obtained. The availability of aluminium in the
days geopolymer can also enhance the soil’s resilience. In terms of curing, the
GGBS in road Na2SiO3 – 0.7 28 [71] rate of temperature has had a number of effects on the microstructure of
subgrade fill soil days geopolymer. Eminent curing temperatures amend structural character­
GGBS with clayey Na2SiO3- – 3.5 28 [72]
soil CCR days
istics such as crystallization and sintering. Moreover, the size of the soil
GGBS with NaOH + 17.4 – 28 [73] pore structure is influenced by densification and over hydration of soil
dredged sludge Na2SiO3 days particles. The significant assets and experiments examined in the literary
GGBS with clayey NaOH 0.85 24.26 28 [74] works are encapsulated in Fig. 18.
soil days
GGBS with black NaOH – 41.5 28 [75]
cotton soil days 7. Analysis of various geopolymer precursors
GGBS/BOFS with CaO + 0.3 7.41 and 8.44 90 [78]
soft clay MgO days In this portion, a comparison of the alkaline binder ratio, alkaline
RHA with peat NaOH 0.7 1.39,1.2, 28 [79] activator, compressive strength, and curing time was performed
(sapric, fibric, and1.12 days
hemic)
(Table 1). This distinct comparable analysis makes it simple to deter­
RHA/FA with NaOH + – 1.5 7 days [84] mine the best source material for the soil during solidification and future
black cotton Na2SiO3 research. Table 1 summarizes the efficiency of geopolymer-stabilized
soils soils in terms of strength, durability, and permeability. The main
MKG in lean clay NaOH + 0.45 31.22 28 [48]
parameter (curing time) was studied to anticipate the UCS of soft soils.
Na2SiO3 days
MKG with clay KOH – 0.85 28 [86] The optimum value of UCS and curing time was found to be 29.3 MPa
days and 90 days, respectively. Therefore, the geopolymer stabilized soils can
MKG with clayey NaHCO3 0.5 0.15 7 days [88] have better strength results. However, a better comprehension of geo­
soil + CaO polymerization in soils has yet to be attained, and further study is
MKG with Loess NaOH + 23900 N 28 [89]
required to validate the potency of geopolymers.
–
soil Na2SiO3 days
MKG with clay NaOH 0.7 4109kN 28 [90]
days 8. Conclusions and future study prerequisites

Geopolymers have been identified as commendable replacements for

16
F. Ayub and S.A. Khan Construction and Building Materials 404 (2023) 133195

traditional stabilization techniques due to amplified strength, decreased only at the beginning of our investigation into possible geopolymer soil
shrinkage, porosity, and so on. Following an examination of several interplay. In literary works, SEM is practically the only method for
studies, conclusions were reached. They were all looking into the pro­ analyzing soil-geopolymer blending. The transparent illustrations of
spective exploit of geopolymer pastes to enhance the mechanical geopolymers clutching soil particles, tying the soil grains together, and
behavior of weak soil. completing gaps help to clarify the interplay. Even so, it is uncertain
whether this sort of reaction is tangible or if certain ingredients are
1. The geopolymers compiled by incorporating industrial wastes generated as an outcome of geopolymer-soil interactions. Addressing
were discovered to efficaciously improve soil solidification these problems would ultimately reveal the methodologies of geo­
behavior. polymer stabilization, as well as determine the best geopolymers
2. A solution of Na2SiO3 and NaOH can amplify strength. Soil so­ depending on the soil circumstances. Furthermore, alkaline binder
lidification via geopolymer compiled with slag can thus be an compositions must be optimized to minimize their environmental im­
efficient and cost-effective technique for enhancing the me­ plications. The manufacturing and transportation of NaOH and Na2SiO3
chanical characteristics of the soil. generate considerable levels of CO2 that need to be mitigated to the
3. The establishment of geopolymer emulsions in soil was validated maximum extent feasible in order to lessen global warming.
by SEM-XRD. Because no novel minerals were developed after
solidification, the bonding impact of the geopolymer emulsions
inevitably enhanced the mechanical characteristics of soft soils. Declaration of Competing Interest
4. Soil stabilization with industrial waste-based geopolymers could
benefit ground improvement, sub-base, and base course of flex­ The authors declare that they have no known competing financial
ible pavements. Furthermore, not only does this soil stabilization interests or personal relationships that could have appeared to influence
method make better use of industrial solid waste, but it is also the work reported in this paper.
extremely cost-effective and environmentally sustainable.
5. The use of geopolymer-treated industrial waste conserves natural Data availability
resources, is ecofriendly, and helps minimize disposal over agri­
cultural farmlands. Data will be made available on request.
6. Stabilizer type, concentration, alkaline ratio, proportion, and
curing time are significant characteristics influencing the UCS of References
alkaline activator specimens.
7. Most exploratory research for geopolymer soil stabilization fo­ [1] H. Javdanian, S. Lee, Evaluating unconfined compressive strength of cohesive
soils stabilized with geopolymer: a computational intelligence approach, Eng.
cuses on a few materials, such as fly ash, POFA, and metakaolin, Comput. 35 (1) (2019) 191–199.
instead of other varieties of precursors. As a result, the decision [2] H. Afrin, A review on different types soil stabilization techniques, Int. J. Transp.
on how to use and dispose of the remaining precursors becomes Eng. Technol. 3 (2) (2017) 19–24.
[3] A.R. Al-Adhadh, Z.J. Kadhim, Z.T. Naeem, Reviewing the most suitable Soil
ambiguous. Thus, it is obligatory to amplify the researcher’s Improvement Techniques for treating soft clay soil, J. Eng. Res. Appl. 9 (8) (2019)
comprehension of the remaining types of industrial source 1–11.
materials. [4] S.M. Marandi, H. Javdanian, Laboratory studies on bearing capacity of strip
interfering shallow foundations supported by geogrid-reinforced sand, in:
8. It is now feasible to reduce the cement manufacturing process and Advanced Materials Research, Vol. 472, Trans Tech Publications Ltd., 2012,
the excavation of lime resources by using industrial waste based- pp. 1856–1869.
geopolymers. [5] Hamzah, H. N., Al Bakri Abdullah, M. M., Heah, C. Y., ArifZainol, M. R. R.,
&Hussin, K. (2015). Review of soil stabilization techniques: Geopolymerization
9. Geopolymer-stabilized soil displayed remarkable tolerance to W-
method one of the new technique. In Key Engineering Materials (Vol. 660, pp. 298-
D and freezing-thawing cycles, as well as slaking water and 304). Trans Tech Publications Ltd.
highly corrosive surroundings. The geopolymer content and [6] H. Javdanian, On the behaviour of shallow foundations constructed on reinforced
soil slope–a numerical analysis, Int. J. Geotech. Eng. 14 (2) (2020) 188–195.
curing time both have an impact on microstructural advance­
[7] Y. Wang, P. Guo, H. Lin, X. Li, Y. Zhao, B. Yuan, Y. Liu, P. Cao, Numerical analysis
ment, implying the development of geopolymeric reaction of fiber-reinforced soils based on the equivalent additional stress concept, Int. J.
products. Geomech. 19 (11) (2019).
10. The employment of industrial wastes in geopolymer soil stabili­ [8] J. Huang, R.B. Kogbara, N. Hariharan, E.A. Masad, D.N. Little, A state-of-the-art
review of polymers used in soil stabilization, Constr. Build. Mater. 305 (2021),
zation can produce an encouraging stiffening effect, comparable 124685.
to the traditional processes, and can reveal to be an improved [9] P. Ghadir, N. Ranjbar, Clayey soil stabilization using geopolymer and Portland
option to traditional treatment procedures. cement, Constr. Build. Mater. 188 (2018) 361–371.
[10] Y. Yi, L. Gu, S. Liu, Microstructural and mechanical properties of marine soft clay
11. For UCS prediction, the effectiveness of the Group method of data stabilized by lime-activated ground granulated blastfurnace slag, Appl. Clay Sci.
handling (GMDH)-based model was contrasted to that of the 103 (2015) 71–76.
artificial neural network (ANN)-based model. The contrast [11] F.E. Jalal, Y. Xu, B. Jamhiri, S.A. Memon, On the recent trends in expansive soil
stabilization using calcium-based stabilizer materials (CSMs): A comprehensive
proved the NF-GMDH-PSO model’s high precision in assessing review, Adv. Mater. Sci. Eng. 2020 (2020) 1–23.
UCS of geopolymer-stabilized soils. [12] Ingles, O.G., Metcalf, J.B. (1972). Soil stabilization principles and practice (Vol.
11, No. Textbook).
[13] U. Calik, E. Sadoglu, Classification, shear strength, and durability of expansive
For geopolymer stabilization mechanisms, numerous explanations
clayey soil stabilized with lime and perlite, Nat. Hazards 71 (3) (2014)
have been propounded, including hydrogen bonding, electrostatic in­ 1289–1303.
teractions, entropy upsurge, physical adhering, etc. These techniques, [14] A.E. Ramaji, A review on the soil stabilization using low-cost methods, J. Appl.
Sci. Res. 8 (4) (2012) 2193–2196.
however, have yet to be confirmed and are not thoroughly grasped.
[15] E. Coudert, M. Paris, D. Deneele, G. Russo, A. Tarantino, Use of alkali activated
Nuclear magnetic resonance (NMR), FTIR, SEM, and XRD, along with high-calcium fly ash binder for kaolin clay soil stabilisation: Physicochemical
many others, have been extensively employed to investigate the evolution, Constr. Build. Mater. 201 (2019) 539–552.
mineralogical composition, morphological characteristics, and chemis­ [16] Y. Liu, C.-W. Chang, A. Namdar, Y. She, C.-H. Lin, X. Yuan, Q. Yang, Stabilization
of expansive soil using cementing material from rice husk ash and calcium
try of soil minerals and geopolymers, as well as potential connections carbide residue, Constr. Build. Mater. 221 (2019) 1–11.
amongst geopolymers and soils. XRD, on the other hand, is best suited [17] E. Adeyanju, C.A. Okeke, I. Akinwumi, A. Busari, Subgrade Stabilization using
for analyzing crystalline minerals like soils, whereas FTIR and NMR are Rice Husk Ash-based Geopolymer (GRHA) and Cement Kiln Dust (CKD), Case
Studies Constr. Mater. 13 (2020), e00388.
primarily utilized for geopolymer assessment. Even though knowing soil [18] S. Andavan, B. Maneesh Kumar, Case study on soil stabilization by using bitumen
mineralogical composition and geopolymer chemistry is critical, we are emulsions–A review, Mater. Today:. Proc. 22 (2020) 1200–1202.

17
F. Ayub and S.A. Khan Construction and Building Materials 404 (2023) 133195

[19] R. Alqaisi, T.M. Le, HadiKhabbaz, Applications of recycled sustainable materials [50] P. Ghadir, M. Zamanian, N. Mahbubi-Motlagh, M. Saberian, J. Li, N. Ranjbar,
and by-products in soil stabilization, in: International Congress and Exhibition“ Shear strength and life cycle assessment of volcanic ash-based geopolymer and
Sustainable Civil Infrastructures”, Springer, Cham, 2019, pp. 91–117. cement stabilized soil: A comparative study, Transp. Geotech. 31 (2021), 100639.
[20] A. Choobbasti, M. AmozadehSamakoosh, S.S. Kutanaei, Mechanical properties [51] S.R. Abdila, M.M.A.B. Abdullah, R. Ahmad, D.D. Burduhos Nergis, S.Z.A. Rahim,
soil stabilized with nano calcium carbonate and reinforced with carpet waste M.F. Omar, A.V. Sandu, P. Vizureanu, Syafwandi, Potential of soil stabilization
fibers, Constr. Build. Mater. 211 (2019) 1094–1104. using ground granulated blast furnace slag (GGBFS) and fly ash via
[21] J. Wang, F.u. Hongtao, F. Liu, Y. Cai, J. Zhou, Influence of electro-osmosis geopolymerization method: A review, Materials 15 (1) (2022) 375.
activation time on vacuum electro-osmosis consolidation of a dredged slurry, [52] H. Miraki, N. Shariatmadari, P. Ghadir, S. Jahandari, Z. Tao, R. Siddique, Clayey
Can. Geotech. J. 55 (1) (2018) 147–153. soil stabilization using alkali-activated volcanic ash and slag, J. Rock Mech.
[22] F. Ayub, S.A. Khan, S.R. Paul, Praseodymium-oxide decorated montmorillonite Geotech. Eng. 14 (2) (2022) 576–591.
nanocomposite as a novel admixture for dredged soil stabilisation, Geomech. [53] N. Shariatmadari, H. Hasanzadehshooiili, P. Ghadir, F. Saeidi, F. Moharami,
Geoeng. (2022) 1–12. Compressive strength of sandy soils stabilized with alkali-activated volcanic ash
[23] A.A. Disu, P.K. Kolay, A critical appraisal of soil Stabilization using geopolymers: and slag, J. Mater. Civ. Eng. 33 (11) (2021), 04021295.
The past, present and future, Int. J. Geosynth. Ground Eng. 7 (2) (2021) 1–16. [54] A.L. Murmu, N. Dhole, A. Patel, Stabilisation of black cotton soil for subgrade
[24] D. Parthiban, D.S. Vijayan, E. Koda, M.D. Vaverkova, K. Piechowicz, P. Osinski, D. application using fly ash geopolymer, Road Mater. Pavement Des. 21 (3) (2020)
B. Van, Role of Industrial based Precursors in the Stabilization of weak soils with 867–885.
geopolymer-A review, Case Stud. Constr. Mater. (2022), e00886. [55] A.L. Murmu, A. Jain, A. Patel, Mechanical properties of alkali activated fly ash
[25] J. Davidovits, years of successes and failures in geopolymer applications. Market geopolymer stabilized expansive clay, KSCE J. Civ. Eng. 23 (9) (2019)
trends and potential breakthroughs, in: Geopolymer 2002 conference, Vol. 28, 3875–3888.
Geopolymer Institute, Saint-Quentin, France; Melbourne, Australia, 2002, p. 29. [56] S. Alsafi, N. Farzadnia, A. Asadi, B.K. Huat, Collapsibility potential of gypseous
[26] J. Davidovits, Geopolymers: inorganic polymeric new materials, J. Therm. Anal. soil stabilized with fly ash geopolymer; characterization and assessment, Constr.
Calorim. 37 (8) (1991) 1633–1656. Build. Mater. 137 (2017) 390–409.
[27] J. He, J. Zhang, Y. Yu, G. Zhang, The strength and microstructure of two [57] H.H. Abdullah, M.A. Shahin, M.L. Walske, Geo-mechanical behavior of clay soils
geopolymers derived from metakaolin and red mud-fly ash admixture: a stabilized at ambient temperature with fly-ash geopolymer-incorporated
comparative study, Constr. Build. Mater. 30 (2012) 80–91. granulated slag, Soils Found. 59 (6) (2019) 1906–1920.
[28] G.P. Zhang, J.A. He, R.P. Gambrell, Synthesis, Characterization, and mechanical [58] S.D. Khadka, P.W. Jayawickrama, S. Senadheera, B. Segvic, Stabilization of
properties of red mud-based geopolymers, Transp Res 2167 (2010) 1–9. highly expansive soils containing sulfate using metakaolin and fly ash based
[29] K.J. MacKenzie, D. Brew, R. Fletcher, C. Nicholson, R. Vagana, M. Schmücker, geopolymer modified with lime and gypsum, Transp. Geotech. 23 (2020),
Advances in understanding the synthesis mechanisms of new geopolymeric 100327.
materials, Novel Processing of Ceramics and Composites: Ceramic Transactions [59] M.A. Mahrous, B. Šegvić, G. Zanoni, S.D. Khadka, S. Senadheera, P.
Series 195 (2006) 185–199. W. Jayawickrama, The role of clay swelling and mineral neoformation in the
[30] C.K. Yip, G.C. Lukey, J.S. Van Deventer, The coexistence of geopolymeric gel and stabilization of high plasticity soils treated with the fly ash-and metakaolin-based
calcium silicate hydrate at the early stage of alkaline activation, Cem. Concr. Res. geopolymers, Minerals 8 (4) (2018) 146.
35 (9) (2005) 1688–1697. [60] A. Kampala, S. Horpibulsuk, N. Prongmanee, A. Chinkulkijniwat, Influence of
[31] K. Chen, D. Wu, Z. Zhang, C. Pan, X. Shen, L. Xia, J. Zang, Modeling and wet-dry cycles on compressive strength of calcium carbide residue–fly ash
optimization of fly ash–slag-based geopolymer using response surface method stabilized clay, J. Mater. Civ. Eng. 26 (4) (2014) 633–643.
and its application in soft soil stabilization, Constr. Build. Mater. 315 (2022), [61] K. Amnadnua, W. Tangchirapat, C. Jaturapitakkul, Strength, water permeability,
125723. and heat evolution of high strength concrete made from the mixture of calcium
[32] Y. Wang, X. Liu, W. Zhang, Z. Li, Y. Zhang, Y. Li, Y. Ren, Effects of Si/Al ratio on carbide residue and fly ash, Mater. Des. 51 (2013) 894–901.
the efflorescence and properties of fly ash based geopolymer, J. Clean. Prod. 244 [62] I. Phummiphan, S. Horpibulsuk, T. Phoo-ngernkham, A. Arulrajah, S.L. Shen,
(2020), 118852. Marginal lateritic soil stabilized with calcium carbide residue and fly ash
[33] D. Khale, R. Chaudhary, Mechanism of geopolymerization and factors influencing geopolymers as a sustainable pavement base material, J. Mater. Civ. Eng. 29 (2)
its development: a review, J. Mater. Sci. 42 (3) (2007) 729–746. (2017) 04016195.
[34] M. Yaghoubi, A. Arulrajah, M.M. Disfani, S. Horpibulsuk, M.W. Bo, S. Darmawan, [63] C. Phetchuay, S. Horpibulsuk, A. Arulrajah, C. Suksiripattanapong, A. Udomchai,
Effects of industrial by-product based geopolymers on the strength development Strength development in soft marine clay stabilized by fly ash and calcium
of a soft soil, Soils Found. 58 (3) (2018) 716–728. carbide residue based geopolymer, Appl. Clay Sci. 127 (2016) 134–142.
[35] P. Rovnaník, Effect of curing temperature on the development of hard structure of [64] M. Aslam, M.A. Kalyar, Z.A. Raza, Polyvinyl alcohol: A review of research status
metakaolin-based geopolymer, Constr. Build. Mater. 24 (7) (2010) 1176–1183. and use of polyvinyl alcohol based nanocomposites, Polym. Eng. Sci. 58 (12)
[36] P. Duxson, J.L. Provis, G.C. Lukey, S.W. Mallicoat, W.M. Kriven, J.S. Van (2018) 2119–2132.
Deventer, Understanding the relationship between geopolymer composition, [65] H.M. Al-Baghdadi, Experimental study on sulfate resistance of concrete with
microstructure and mechanical properties, Colloids Surf A Physicochem Eng Asp recycled aggregate modified with polyvinyl alcohol (PVA), Case Stud. Constr.
269 (1–3) (2005) 47–58. Mater. 14 (2021), e00527.
[37] D. Hardjito, S. Wallah, D.J. Sumajouw, B. Vijaya Rangan, On the development of [66] W. Jiang, X. Li, Y. Lv, M. Zhou, Z. Liu, Z. Ren, Z. Yu, Cement-based materials
Fly ash-based Geopolymer concrete, ACI Mater. J. (2004). containing graphene oxide and polyvinyl alcohol fiber: mechanical properties,
[38] Wallah, S., Rangan, B.V. (2006). Low-calcium fly ash-based geopolymer concrete: durability, and microstructure, Nanomaterials 8 (9) (2018) 638.
long-term properties. [67] M. Mirzababaei, A. Arulrajah, S. Horpibulsuk, A. Soltani, N. Khayat, Stabilization
[39] S. Ahmari, L. Zhang, The properties and durability of mine tailings-based of soft clay using short fibers and poly vinyl alcohol, Geotext. Geomembr. 46 (5)
geopolymeric masonry blocks, in: Eco-Efficient Masonry Bricks and Blocks, (2018) 646–655.
Woodhead Publishing, 2015, pp. 289–309. [68] C. Suksiripattanapong, S. Horpibulsuk, C. Yeanyong, A. Arulrajah, Evaluation of
[40] P. Duxson, G.C. Lukey, F. Separovic, J.S.J. Van Deventer, Effect of alkali cations polyvinyl alcohol and high calcium fly ash based geopolymer for the
on aluminium incorporation in geopolymeric gels, Ind. Eng. Chem. Res. 44 (4) improvement of soft Bangkok clay, Transp. Geotech. 27 (2021), 100476.
(2005) 832–839. [69] S.B. Yamgar, S.R. Takkalaki, Study and analysis of strength of GGBS concrete, Int.
[41] M. Steveson, K. Sagoe-Crentsil, Relationships between composition, structure and J. Eng. Manage. Res. (IJEMR) 8 (6) (2018) 28–47.
strength of inorganic polymers, J. Mater. Sci. 40 (8) (2005) 2023–2036. [70] A. Thomas, R.K. Tripathi, L.K. Yadu, A laboratory investigation of soil
[42] A. Arulrajah, M. Yaghoubi, M.M. Disfani, S. Horpibulsuk, M.W. Bo, M. Leong, stabilization using enzyme and alkali-activated ground granulated blast-furnace
Evaluation of fly ash-and slag-based geopolymers for the improvement of a soft slag, Arab. J. Sci. Eng. 43 (10) (2018) 5193–5202.
marine clay by deep soil mixing, Soils Found 58 (6) (2018) 1358–1370. [71] N.J. Jiang, Y.J. Du, K. Liu, Durability of lightweight alkali-activated ground
[43] N. Shariatmadari, H. Mohebbi, A.A. Javadi, Surface stabilization of soils granulated blast furnace slag (GGBS) stabilized clayey soils subjected to sulfate
susceptible to wind erosion using volcanic ash-based geopolymer, J. Mater. Civ. attack, Appl. Clay Sci. 161 (2018) 70–75.
Eng. 33 (12) (2021), 04021345. [72] Y.J. Du, B.W. Yu, K. Liu, N.J. Jiang, M.D. Liu, Physical, hydraulic, and mechanical
[44] J.-H. Yin, W.-H. Zhou, Influence of grouting pressure and overburden stress on properties of clayey soil stabilized by lightweight alkali-activated slag
the interface resistance of a soil nail, J. Geotech. Geoenviron. Eng. 135 (9) (2009) geopolymer, J. Mater. Civ. Eng. 29 (2) (2017), 04016217.
1198–1208. [73] L. Lang, B. Chen, B. Chen, Strength evolutions of varying water content-dredged
[45] A. Bosoaga, O. Masek, J.E. Oakey, CO2 capture technologies for cement industry, sludge stabilized with alkali-activated ground granulated blast-furnace slag,
Energy Procedia 1 (1) (2009) 133–140. Constr. Build. Mater. 275 (2021), 122111.
[46] A.H. Bushlaibi, A.M. Alshamsi, Efficiency of curing on partially exposed high- [74] D. Rezazadeh Eidgahee, A.H. Rafiean, A. Haddad, A novel formulation for the
strength concrete in hot climate, Cem. Concr. Res. 32 (6) (2002) 949–953. compressive strength of IBP-based geopolymer stabilized clayey soils using ANN
[47] M.R. Irshidat, N. Al-Nuaimi, W. Ahmed, M. Rabie, Feasibility of recycling waste and GMDH-NN approaches, Iran. J. Sci. Technol., Trans. Civil Eng. 44 (1) (2020)
carbon black in cement mortar production: Environmental life cycle assessment 219–229.
and performance evaluation, Constr. Build. Mater. 296 (2021), 123740. [75] V. Noolu, G. Mallikarjuna Rao, B. Sudheer kumar reddy, R.V.P. Chavali, Strength
[48] M. Zhang, H. Guo, T. El-Korchi, G. Zhang, M. Tao, Experimental feasibility study and durability characteristics of GGBS geopolymer stabilized black cotton soil,
of geopolymer as the next-generation soil stabilizer, Constr. Build. Mater. 47 Mater. Today:. Proc. 43 (2021) 2373–2376.
(2013) 1468–1478. [76] A.S. Reddy, R.K. Pradhan, S. Chandra, Utilization of Basic Oxygen Furnace (BOF)
[49] B. Singhi, A.I. Laskar, M.A. Ahmed, Investigation on soil–geopolymer with slag, slag in the production of a hydraulic cement binder, Int. J. Miner. Process. 79 (2)
fly ash and their blending, Arab. J. Sci. Eng. 41 (2) (2016) 393–400. (2006) 98–105.

18
F. Ayub and S.A. Khan Construction and Building Materials 404 (2023) 133195

[77] D. Kong, S. Wu, M. Chen, M. Zhao, B. Shu, Characteristics of different types of [91] L. Wei, S.X. Chai, H.Y. Zhang, Q. Shi, Mechanical properties of soil reinforced
basic oxygen furnace slag filler and its influence on properties of asphalt mastic, with both lime and four kinds of fiber, Constr. Build. Mater. 172 (2018) 300–308.
Materials 12 (24) (2019) 4034. [92] S. Wang, Q. Xue, W. Ma, K. Zhao, Z. Wu, Experimental study on mechanical
[78] M. Salimi, A. Ghorbani, Mechanical and compressibility characteristics of a soft properties of fiber-reinforced and geopolymer-stabilized clay soil, Constr. Build.
clay stabilized by slag-based mixtures and geopolymers, Appl. Clay Sci. 184 Mater. 272 (2021), 121914.
(2020), 105390. [93] K.S. Chandra, S. Krishnaiah, N.G. Reddy, N. Hossiney, L. Peng, Strength
[79] S.A. Khanday, M. Hussain, A.K. Das, Rice husk ash-based geopolymer development of geopolymer composites made from red mud-fly ash as a subgrade
stabilization of indian peat: experimental investigation, J. Mater. Civ. Eng. 33 material in road construction, J Hazard., Toxic, Radioactive Waste 25 (1) (2021),
(12) (2021) 04021347. 04020068.
[80] J. He, G. Zhang, Geopolymerization of red mud and rice husk ash and potentials [94] S. Alam, S.K. Das, B.H. Rao, Strength and durability characteristic of alkali
of the resulting geopolymeric products for civil infrastructure applications, activated GGBS stabilized red mud as geo-material, Constr. Build. Mater. 211
Developments in Strategic Materials and Computational Design II: Ceramic (2019) 932–942.
Engineering and Science Proceedings 32 (2011) 45–52. [95] A. Fakhrabadi, M. Ghadakpour, A.J. Choobbasti, S.S. Kutanaei, Evaluating the
[81] H. Chao-Lung, B. Le Anh-Tuan, C. Chun-Tsun, Effect of rice husk ash on the durability, microstructure and mechanical properties of a clayey-sandy soil
strength and durability characteristics of concrete, Constr. Build. Mater. 25 (9) stabilized with copper slag-based geopolymer against wetting-drying cycles, Bull.
(2011) 3768–3772. Eng. Geol. Environ. 80 (6) (2021) 5031–5051.
[82] M.Y. Fattah, F.H. Rahil, K.Y. Al-Soudany, Improvement of clayey soil [96] I.A. Khasib, N.N.N. Daud, N.A.M. Nasir, Strength development and
characteristics using rice husk ash, J. Civil Eng. Urban. 3 (1) (2013) 12–18. microstructural behavior of soils stabilized with palm oil fuel ash (POFA)-based
[83] S.T. Swamy, K.H. Mamatha, S.V. Dinesh, A. Chandrashekar, Strength properties geopolymer, Appl. Sci. 11 (8) (2021) 3572.
of laterite soil stabilized with rice husk ash and geopolymer, in: Problematic Soils [97] P. Sukmak, G. Sukmak, S. Horpibulsuk, M. Setkit, S. Kassawat, A. Arulrajah, Palm
and Geoenvironmental Concerns, Springer, Singapore, 2021, pp. 789–799. oil fuel ash-soft soil geopolymer for subgrade applications: strength and
[84] A.L. Murmu, A. Patel, Studies on the properties of fly ash–rice husk ash-based microstructural evaluation, Road Mater. Pavement Des. 20 (1) (2019) 110–131.
geopolymer for use in black cotton soils, Int. J. Geosynth. Ground Eng. 6 (3) [98] L. Abdeldjouad, A. Asadi, R.J. Ball, H. Nahazanan, B.B. Huat, Application of
(2020) 1–14. alkali-activated palm oil fuel ash reinforced with glass fibers in soil stabilization,
[85] T. Luukkonen, M. Sarkkinen, K. Kemppainen, J. Rämö, U. Lassi, Metakaolin Soils Found. 59 (5) (2019) 1552–1561.
geopolymer characterization and application for ammonium removal from model [99] J.J.A. Baldovino, R.L.S. Izzo, J.L. Rose, M.D.I. Domingos, Strength, durability,
solutions and landfill leachate, Appl. Clay Sci. 119 (2016) 266–276. and microstructure of geopolymers based on recycled-glass powder waste and
[86] R. Samuel, A.J. Puppala, M. Radovic, Sustainability benefits assessment of dolomitic lime for soil stabilization, Constr. Build. Mater. 271 (2021), 121874.
metakaolin-based geopolymer treatment of high plasticity clay, Sustainability 12 [100] J. de Jesús Arrieta Baldovino, R. dos Santos Izzo, J.L. Rose, M.A. Avanci,
(24) (2020) 10495. Geopolymers based on recycled glass powder for soil stabilization, Geotech. Geol.
[87] Y. Luo, J. Meng, D. Wang, L. Jiao, G. Xue, Experimental study on mechanical Eng. 38 (4) (2020) 4013–4031.
properties and microstructure of metakaolin based geopolymer stabilized silty [101] M.P. Bilondi, M.M. Toufigh, V. Toufigh, Experimental investigation of using a
clay, Constr. Build. Mater. 316 (2022), 125662. recycled glass powder-based geopolymer to improve the mechanical behavior of
[88] S. Wang, Q. Xue, Y. Zhu, G. Li, Z. Wu, K. Zhao, Experimental study on material clay soils, Constr. Build. Mater. 170 (2018) 302–313.
ratio and strength performance of geopolymer-improved soil, Constr. Build. [102] R.B. SHokatabad, V. Toufigh, M.M Toufigh, Stabilization of sandy soil with
Mater. 267 (2021), 120469. geopolymers based on nanomaterials and Taftan pozzolan, Amirkabir J. Civ. Eng.
[89] N. Hanegbi, I. Katra, A clay-based geopolymer in loess soil stabilization, Appl. Sci. 52 (9) (2020) 2357–2378.
10 (7) (2020) 2608. [103] X. Wen-Jie, X. Qiang, H. Rui-Lin, Study on the shear strength of soil–rock mixture
[90] X. Shi, Q. Zha, S. Li, G. Cai, D. Wu, C. Zhai, Experimental study on the mechanical by large scale direct shear test, Int. J. Rock Mech. Min. Sci. 48 (8) (2011)
properties and microstructure of metakaolin-based geopolymer modified clay, 1235–1247.
Molecules 27 (15) (2022) 4805.

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