Construction and Building Materials 278 (2021) 122347

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Construction and Building Materials

journal homepage: www.elsevier.com/locate/conbuildmat

Review

Effect of nano-silica in concrete; a review

Abhilash P. P. a,⇑, Dheeresh Kumar Nayak a, Bhaskar Sangoju b, Rajesh Kumar a,
Veerendra Kumar a
a
Department of Civil Engineering, Indian Institute of Technology (BHU), Varanasi 221005, India
b
Structural Engineering Research Centre, CSIR Campus, Taramani P.O., Chennai 600113, India

h i g h l i g h t s

Nano-silica up to 3% can enhance mechanical and durability properties of concrete.

Concrete compressive strength increases as the content of nano-silica increases.

Nano-silica has a very high pozzolanic activity.

Filling effect of nano-silica notably influences the refinement of pore structure.

a r t i c l e i n f o a b s t r a c t

Article history: Concrete has a substantial impact on the environment as the cement, whose production involves a large
Received 13 February 2020 amount of CO2, is its main ingredient. Enhancing the durability parameters of the concrete structures can
Received in revised form 28 December 2020 reduce their impact on the environment. Incorporating a small amount of nanoparticles in concrete can
Accepted 6 January 2021
modify the nano-structure of cementitious materials, and thus procure high durability. Recently nano-
Available online 29 January 2021
silica has gained particular attention compared to conventional mineral addition due to its better perfor-
mance in concrete. This review paper presents a study of the effects of nano-silica on the mechanical
Keywords:
properties, durability parameters, and microstructural characteristics of the concrete.
Nano-silica
Pozzolanic reaction
Ó 2021 Elsevier Ltd. All rights reserved.
Filler effect
Mechanical properties
Durability properties
Hydration
Microstructure
Porosity
Carbonation

Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Effect of nano-silica on properties of fresh concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Effect of nano-silica on properties of hardened concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Compressive strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.2. Tensile strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.3. Flexural strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.4. Modulus of elasticity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.5. Abrasion resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.6. Impact resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.7. Compressive stress strain behaviour/ stress strain relationship. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.8. Non-destructive parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
4. Effect of nano-silica on durability parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
4.1. Pore structure/porosity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

⇑ Corresponding author.
E-mail address: abhilashpp.rs.civ18@iitbhu.ac.in (A. P. P.).

https://doi.org/10.1016/j.conbuildmat.2021.122347
0950-0618/Ó 2021 Elsevier Ltd. All rights reserved.
A. P. P., Dheeresh Kumar Nayak, B. Sangoju et al. Construction and Building Materials 278 (2021) 122347

4.2. Water absorption, sorptivity, water permeability and infiltration rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

4.3. Chloride ion penetration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
4.4. Sulphate attack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
4.5. Carbonation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
4.6. Corrosion resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
4.7. Temperature effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
4.8. Frost resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
4.9. Effect of acid exposure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
5. Fracture behaviour . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
6. Rate of hydration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
7. Microstructure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
8. Effect of size and type of nano silica and its mixing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
9. Combined effect of nS and mS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
10. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Declaration of Competing Interest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

1. Introduction One of the main features of the nanoparticles is their high vol-
ume to the surface area, Fig. 1 [22]. Several nano-sized particles are
Concrete is considered one of the most commonly used materi- used as a nano-additive in the cement-based materials to enhance
als in the world, with an estimated annual production of 27.3 bil- their properties at the macroscopic level and improve their func-
lion tonnes in 2015, making an average of about 1.6 m3 for each tionality, and the silica nanoparticles or nano silica have become
person on the earth [1]. Portland cement, the essential concrete common among those nano-sized particles [23].
binder, accounts for nearly 80% of total concrete CO2, emissions, Nano-silica (nS) or silica nanoparticles, also known as silicon
sharing 5 to 7% of total CO2, emissions on this earth [2–7]. The dioxide nanoparticles, can be used as additives for improving con-
demand for Portland cement is likely to increase by nearly 200% crete’s mechanical and durability properties [24–26]. The effect of
over 2010 rates by 2050, reaching 6,000 million tonnes a year [8]. nS on nanostructure of cement paste also confirmed the improve-
Therefore, the key sustainability challenges for the next decades ment in concrete durability [27]. The results revealed the nS as an
are developing and manufacturing concrete with fewer clinkers excellent alternative to reduce consumption of cement in the pro-
and causing lower carbon dioxide emissions than the traditional duction of high strength concrete (HSC) [28]. Using nS as a cement
ones, while offering the same reliability and much better durability replacement makes concrete more cost-effective and reduces the
[9]. Peris Mora [10] has described the significance of durability in CO2 footprint of the concrete products [29]. Due to their improved
building materials for eco-efficiency, stating that an increase in performance in filling effect and particle size distribution, thereby
concrete durability from 50 years to 500 years could scale down decreasing the porosity in concrete and increasing their pozzolanic
the impact on the environment by a factor of up to 10. Pacheco reaction with calcium hydroxide (Ca (OH)2 or CH) to yield CSH, nS
et al. [8] reported that as much as 50% in the use of reinforced steel has gained particular attention in comparison with conventional
could be reduced by increasing the concrete compressive strength. minerals admixtures [30,31]. Such behaviours of nS resulted in
Durable and high strength concrete is the main concern in its improved mechanical properties in the concrete mix [32–34].
future production as far as material and eco-efficiencies are con- The cement setting process was enhanced by nS compared to silica
cerned [11]. fumes (SF) [35] and decreased bleeding and segregation and
The application of the nanoparticles to enhance the durability increased cohesiveness of fresh mixes [36]. Nano-silica facilitates
and mechanical properties of the cementitious composites was hydration of cement at a very early age, and it can consume and
explored in the report of RILEM Technical Committee 197- convert calcium hydroxide into CSH gel due to its high pozzolanic
Nanotechnology in Construction Materials (TC 197-NCM) [12]. action, thus enhancing the concrete’s mechanical properties [37].
The use of nanoscience and nanotechnology in cementitious com- The morphology of nS in powdered form and under a transmission
posites was reported in late 1980 and became active for almost electron microscope (TEM) is shown in Fig. 2 [38].
two decades [13]. Nanomaterials have excellent properties and R. Olar, in 2011, reported a reduction in the use of nanomateri-
functions that can provide cementitious composites high perfor- als in construction due to lacking knowledge of suitable nanomate-
mance with high mechanical and durability properties and multi- rials and their behaviour, lack of specific design standards for
functionality and intelligence [14–18]. Nano metallic and non- constructing elements using nanomaterials, lack of detailed infor-
metallic oxides cementitious composites were first used to modify mation on the contents of nanoproducts, its high costs and
or enhance the properties of the cementitious materials [19]. unknown health risks involved in handling nanoparticles [39].
Through recognizing the structure at its nanolevel, a new gener- However, a considerable rise in the number of publications in the
ation of high-performance building materials can be updated, syn- area of nanotechnology-based eco-efficient construction materials
thesized, and engineered. With the advancement in technology, is noticed over recent years [23].
the structure of the composites at the atomic level can be observed, Extensive research on choice of the nanomaterials, such as sili-
and their various properties of different phases can be evaluated at con dioxide nanoparticles (Nano-SiO2 or nano-silica), titanium
a nanolevel [20]. The concept of packing of particles at the nanos- dioxide nanoparticles (TiO2), carbon nanotubes, nanoparticles of
cale can, therefore, be used to improve the performance of the zinc oxide (ZnO), silver (Ag), aluminum oxide (Al2O3), and zirco-
composites. This very thought led the researchers into nano- nium oxide (ZrO2), etc., their effects on concrete, and building ele-
silica (nS) particles and nano-fibers in order to enhance strength, ments at different loading conditions and circumstances must be
durability, and processing characteristics of the cement composites carried out to encourage the wide-scale application of nanomateri-
[20]. Novel properties of the nanoparticles of sizes 1–100 nm have als in the construction field [25,39]. Different materials being
drawn immense interest over the past decades [21]. developed for construction industries will revolutionize not only

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A. P. P., Dheeresh Kumar Nayak, B. Sangoju et al. Construction and Building Materials 278 (2021) 122347

Fig. 1. Particle size and specific surface area related to concrete materials, Sobolev et al. [22].

Fig. 2. Morphology of nano-silica a). Nano-silica Powder, b). TEM image of nano-silica, Li et al. [38].

conventional civil engineering and low-tech construction materials Different researchers reported a decrease in workability in nS
but also have a broad positive impact on society [40]. incorporated concrete [37,42,44]. Ghafari et al. [42] reported an
This review paper focuses on illustrating the impact of nS on increase in demand for water as percentage of nS in concrete
fresh and hardened concrete properties when it is mixed into con- increased, which is attributed to the fineness or high specific sur-
crete as an additive or a partial substitute for the cement. face area of nS particles and the immediate interaction between
nS and liquid face cementitious mix [37] and the high-water
absorption level of nS [44].
2. Effect of nano-silica on properties of fresh concrete Mukharjee et al. [45] found that the slump value decreased as
the amount of nS increased in the concrete. Due to the high surface
The interaction of nS particles in fresh concrete shows their area of the nS particles and the unsaturated bonds in nS, a portion
influence on different properties of fresh concrete, such as worka- of the mixing water (water molecules) attracts towards the surface
bility, setting time, consistency, etc. Zhang et al. [34,41] reported of nS particles and thus produces silanol (Si-OH) groups. As a con-
that the use of 2% nS particles in high-volume fly ash (HVFA) and sequence, the water needed for the fluidity of the concrete mixture
slag concrete reduced initial as well as final setting times. Ghafari becomes insufficient, according to [45].
et al. [42] and Jalal et al. [43] also noticed a similar effect of nS on Ghafari et al. [42] observed that for an acceptable range of
setting times in ultra-high-performance concrete (UHPC) and high- slump flow, the highest amount of nS that could be added is 3%
performance self-compacting concrete (HPSCC), respectively [45]. by weight, and the same was also confirmed by [44]. However,
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A. P. P., Dheeresh Kumar Nayak, B. Sangoju et al. Construction and Building Materials 278 (2021) 122347

the research conducted by Jalal et al. [43] on HPSCC showed that resulted in 3 and 4.5% strength gain compared with the control
concrete workability was not much affected by the addition of specimen. However, at 28 days, the gain in strength was 43.5% at
2% nS. Well-dispersed and de-agglomerated nS led to a substantial 3% and 17.5 and 29% respectively at 1.5 and 4.5% nS dosages.
increase of about 35% in concrete workability, and which can be According to the study, the agglomeration of the nS particles
due to the presence of free water among the ultra-fine particles caused a long time for its reaction with excess CH to form CSH
that facilitates the rolling effects between the particles [46]. It indi- gel, and the agglomerated nS particles acted as filler materials,
cates that a better dispersion of nanoparticles can even improve which reduced porosity, causing the improvement of early age
concrete workability. strength. The optimal 3% dose of nS also improved the bond
The studies on recycled aggregate concrete (RAC) containing nS strength by 38.5% compared to the control sample as reported by
found that the water absorbed by the recycled aggregate (RA) and [64]. Singh et al. [24] reported that the nS particle yielded a higher
nS particles resulted in the loss of slump, and the greater was the early age compressive strength in nano-engineered FA concrete. It
loss at the higher nS dosage [47]. Elrahman et al. [48] reported that was observed that the nS particles are highly effective in improving
incorporating nS decreased consistency and thus increased the vis- compressive strength in UHPC at 3 days compared to 7 and 26 days
cosity of the fresh mixture. The content of the air in nS incorpo- implying that the nS particles considerably promote the hydration
rated concrete mixes was high compared with the reference mix process of cement at early ages [9]. The studies [25,26] suggest that
due to the high viscosity of the paste with nanoparticles of the high the nS particles accelerate the early hydration rate and modify the
specific surface area [49]. CSH packing density from low to high. Chithra et al. [65] reported
In self-compacting light weight aggregate concrete (SCLC), higher production of CHS in high performance slag concrete (HPSC)
replacing cement with nS reduced the fresh density and increased with 2% nS at early ages with a very compact structure. The high
its consistency [50]. Cho et al. [51] reported that the rheological density CSH is responsible for the high early strength and at later
behaviour of lightweight foam concrete (LWFC) improved by add- age the hydration process is impeded by the reduced porosity of
ing a small amount of nS particles as the stress growth rheometer the concrete in the presence of nS particles [66].
test showed a significant increase in static and dynamic yield According to the recent study in nS concrete [45], the increase
stresses. in early age compressive strength is due to the high pozzolanic
activity of nS at early age. Whereas the increase in 28 days com-
pressive strength is due to the filling up of voids by the CSH gel
3. Effect of nano-silica on properties of hardened concrete formed and strengthened mortar-aggregated bonding. The smaller
and finer nS particles filled the space between the grains in the
3.1. Compressive strength cement paste and caused the development of the strength, accord-
ing to [67].
According to studies [34,41,42,48,52–57], even a small dose of Dolomite concrete containing 2% nS exhibited a higher com-
nS in concrete at their early ages can significantly enhance the pressive strength; however, the strength reduced at 4% nS [68]. Fal-
compressive strength. The maximum early and 28 days compres- lah et al. [69] reported that the compressive strength increased by
sive strength observed at 2 to 3% replacement of nS indicates that 14 and 8.6%, respectively, in the HSC with macro-polymeric and
the optimum dose of nS lies within this range [34,37,41– polypropylene fibers, at 2 and 3% nS. The result also showed that
43,53,54,58,59]. 3% nS with 0.2% polypropylene (PP) contributed a 13.5% increase
Nano-silica with small particle size exhibited a higher early age in strength compared to the plain concrete.
strength in comparison to bigger particles [41]. Naji Givi et al. [60] Because of the increased formation of hydration products in the
reported that nS with 15 nm average particle size increased con- presence of nS particles, the mechanical properties of GGBFS
crete strength at the early ages as compared to 80 nm particles, admixed self-compacting concrete (SCC) increased by adding up
but the 90 days compressive strength was higher in concrete with to 3% nS particles [70]. The study also found that nS particles above
80 nm nS particles. Belkowitz et al. [61] observed that cement 3% resulted in a lowered strength due to the reduction in crys-
composite with larger nS particles exhibited higher levels of talline CH content needed for CSH gel formation. In a study by Hei-
enhancement in compressive strength and elastic modulus by dari et al. [71], it was observed that adding 0.5 to 1% nS to ground
more than 20% of the reference mixtures. Belkowitz’s study also ceramic powder concrete improved the negative effects of ground
recorded a 20% increase in compressive strength at the lowest ceramic powder on the mechanical properties of concrete.
doses of smallest (5 nm) nS particles and a 14% reduction in com- The high reactivity of nS with the CH produced during the pro-
pressive strength at their highest doses, compared to the reference cess of hydration resulted in an increase of compressive and tensile
concrete. This reduction of strength at high nS dosage is attributed strengths of the HPSCC at the early ages and a large amount of
to more agglomerated sites and voids produced by the high con- reaction products formed due to the subsequent hydration acceler-
tent of small nS particles in concrete. According to Elkady et al. ation [43]. According to Puentes et al. [72], the high evaporation
[46] the agglomeration of the nS particle could result in loss or gain rate in SCC with smaller nS particles induced large open porosity
of compressive strength depending upon the degree of agglomera- at 7 days; however, at 28 days, the high pozzolanic activity
tion. Li et al. [62] reported that the difficulty in achieving uniform increased the strength of SCC. Hameed et al. [73] reported an
dispersion of nS (10 ± 5 nm size) in concrete at their higher dosage increase in SCC compressive strength with increased colloidal nS
caused the formation of weak zones in concrete as the study (CnS) content and found that the compressive strength increased
showed a higher compressive strength for 1% nS compared to 3% from 29.32% to 48.1%, compared to the reference concrete, as the
nS concrete. It may be hypothesized that small nS particle agglom- CnS increased from 2.5% to 10%, respectively at 28 days. A steady
eration could have created the weak zones. Li et al. also observed increase in compressive strength was also reported by Massana
poor workability at a higher dose of nS, which led to developing et al. [74] with the addition of nS up to 7.5% in HPSCC, but the
microcracks in concrete. However, the investigation by Saloma increase was only around 13% at 28 days compared to the refer-
et al. [63] on nanomaterial concrete reported that the compressive ence mix. However, relative to the reference mix, this study
strength increased as the nS content increased up to 10%. reported the highest increase in compressive strength of 31% when
Elkady et al. [64] reported a 13.5% gain in compressive strength 2.5% of nS and mS used in combination. This is attributed to,
at 4.5% nS dosage in nS concrete at 7 days while 1.5 and 3% nS according to de Abreu et al. [28] a synergy effect or a combined

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A. P. P., Dheeresh Kumar Nayak, B. Sangoju et al. Construction and Building Materials 278 (2021) 122347

effect of both nS and mS in the concrete, which is of chemical in and 6.8% in two years. Inclusion of nS in HVFA concrete enhanced
nature in addition to the physical effect which led the concrete par- both the early age and 28 days compressive strengths [54] and is
ticles to be better packed. comparable to the results obtained by [34]. At 28 days, the addition
At all the stages of the test from 3 to 91 days, the SCC showed of 3 and 6% nS to concrete with 30% fly ash (FA) exhibited compres-
the highest compressive strength for colloidal nS (CnS) compared sive strength equal to or greater than that of non-fly ash concrete
to its powdered form, and at the same time, the reference and pow- [84]. The nS concrete achieved the characteristic compressive
dered nS concrete specimens displayed the same compressive strength in half of the time required by the reference concrete
strength at 7 and 28 days [49]. However, according to the above and concrete with micro-silica (mS) to achieve the same strength
investigation, the first day strength of the reference concrete was [56]. Concrete samples with 1% nS and with 1% nS plus 25% FA
more than that of nS concrete. Puentes et al. 2015 [72] reported showed the same compressive strengths at 29th and 87th day tests
a lower strength in nS incorporated SCC at 1 day but a higher [76]. Results also showed that nS addition improved the long-term
strength at 28 days. Addition of nS solution to the concrete mix strength development in HVFA concrete with 40% FA [54].
in comparison with an equivalent amount of powdered nS moder- Researchers have compared the effect of nS and silica fume (SF)
ately improved the concrete strength after 28 days but not the or mS on the properties of different types of concrete. Hasan-Nattaj
early strength [75]. et al. [44] reported that SF exhibited better performance than the
Alhawat et al. [55] reported that the ultra-high surface area of nS for improving the compressive strength in the steel-fiber con-
nS increased the acceleration of the hydration process. The large crete. Singh et al. [24] reported a 40% strength gain within 28 to
quantity of hydration products made the concrete denser and more 90 days for concrete with 30% FA and with 30% FA plus 6% SF, on
homogeneous [42] than the ordinary concrete as the voids in the the other hand, in the concrete with 30% FA plus 3% nS mix, the
micro cement particles were filled by the nanoparticles of the silica gain in strength was reduced to 19%. As stated earlier, this may
[76]. Du et al. [77] reported that due to the high hydration rate in be due to the increased hydration rate at the early stage and mod-
the presence of nS particles, the early age strength of the light- ification low-density structure of CSH to its high-density structure
weight concrete (LWC) was improved; however, such gain in in the presence of nS [25,26]. However, according Bastami et al.
strength was diminished with prolonged curing time. The self- [85], the addition of nS in HSC was more effective than the addition
compacting light weight aggregate concrete (SCLC) showed a of SF to enhance the residual compressive strength of the heated
higher 28 days compressive strength at 0.25, 0.37 and 0.5 water- specimens.
binder (w/b) ratio for the replacement level of nS up to 5% [50]. In UHPC, with increased nS content up to 1%, the flexural to
Adding 3% nS to high strength light weight concrete (HSLWC) min- compressive strength ratio increased, and the nS content of more
imized the negative effect of the coarse lightweight aggregate and than 1% contributed to a decrease in this ratio [38]. The study also
contributed to a significant improvement in mechanical properties observed that cement replacement with optimal content of 1% nS
of the concrete [67]. Elrahman et al. [48] noted an increase in com- and 3% nano-limestone (nC) in UHPC increased the mechanical
pressive strength in LWC with nS up to 4%. strength and formed a dense microstructure.
Naji Givi et al. [78] and Nazari et al. [79] observed that cement In the case of recycled aggregate concrete (RAC), due to
could be replaced advantageously with 2% nS of 15 nm average improved concrete quality, a consistent improvement in compres-
particle size while the samples cured in the solution of lime for sive strength was also noticed at 7, 24, and 90 days, with an addi-
28 days, however, for the water cured samples the optimum tion of 3% nS, according to Mukharjee et al. [47]. Erdem et al. [86]
amount of nS was only 1%. It may be ascribed to the excessive reported an improvement of compressive strength in RAC even at a
nanoparticles (pozzolans) than that required, in water curing, to small dose of 0.5, 1, and 1.5% nS due to quickened hydration pro-
react with lime liberated during the process of hydration, thus cess and pozzolanic reaction, which resulted in forming a strong
causing leaching of excessive silica and subsequent strength defi- bond between mortar and aggregates. The application of silica
ciency as it replaces with a portion of the cementitious material nanoparticles at a small amount of 0.4, 0.8, and 1.2% resulted in
and not contributing to the further improvement in the strength a compressive strength increase of 10, 18 and 22% for mixtures
[80]. While lime curing, a large amount of CSH gel was formed as containing 50% recycled aggregate (RA) and 6, 13 and 16% for mix-
the amount of nS (pozzolan) present in the concrete mixture was tures with 100% RA, respectively [87].
close enough to react with lime liberated during the process of Fig. 3 gives a comparison of the compressive strength of con-
hydration and causing less silica to leach out compared to the crete with 3% nS at 0.4 w/c and Fig. 4 gives the effect of nS on com-
water cured samples [78]. pressive strength in different concretes with its different dosages
The rapid development of the compressive strength of nS con- at different ages. The details of the studies are given in Tables 1
crete showed that nS acts as a filler to increase the concrete density and 2.
and an activating agent for hydration reaction [81]. Experimental
results [75] of plain concrete indicated that by incorporating just 3.2. Tensile strength
0.1% nS in to it increased the strength by 84%, 93%, and 35% at 3,
7, and 28 days, respectively, for the water cement ratios (w/c) Studies show that nS applied concrete has a higher tensile
between 0.42 and 0.45. The concrete with 0.65 w/b ratio yielded strength in comparison to the ordinary and mineral admixed con-
a substantial increase of 41% in 28 days compressive strength at cretes. Hasan-Nattaj et al. [44] reported that the tensile strength of
1.5% nS, while the gain was only 6.5 and 0%, respectively, at 0.55 steel-fiber reinforced concrete containing 2% nS was increased by
and 0.5 w/b ratios [82]. Makarova et al. [75] reported that the 8.2% and 80.6%, respectively, relative to the fiber-reinforced con-
increase in nS content from 0.05% to 0.5% considerably improved crete and plain concrete. The HPSCC exhibited a marked increase
the strength of the concrete but, further increase of nS to 1% did of splitting tensile strength through the inclusion of 2% nS and
not affect the strength. According to Du et al. [52], the decrease 10% SF, due to the high reactivity of nS to consume CH formed dur-
in porosity and refined pore structure due to the pozzolanic reac- ing the hydration [43]. It was observed by Naji Givi et al. [60] that
tion at a small dose of 0.3% nS in concrete increased the early the compressive strength, together with the tensile and flexural
age compressive strength. strengths of the nS blended cement concrete were high for all ages
Application of nS increased both the short and long-term of moist curing up to 90 days compared to non-nS concrete, but the
strength of HVFA concrete [83] as concrete with 50% FA and 4% effect of nS with 80 nm size was more noticeable than that with
nS showed an 81% rise in strength in one day, 9.5% in one year, 15 nm particles. The concrete with nS particles of 10–140 nm size
5
A. P. P., Dheeresh Kumar Nayak, B. Sangoju et al. Construction and Building Materials 278 (2021) 122347

Fig. 3. Compressive strength of concrete with 3% nS and 0.4 w/c ratio.

Fig. 4. Compressive strength of different types of concrete at different nS dosages and w/b ratios.

Table 1
The effect of 3% nS on concrete compressive strength at 0.4 w/c ratio.

Author Type of Size/Surface Remarks

nS area of nS
Mukharjee et al., Colloidal 8–20 nm In the concrete with3% nS at 28 days, the compressive strength increased by 20%, compared to the reference
2020[45] concrete. The same trend was observed at 90 and 365 days of compressive strength test.
Varghese et al., Colloidal 40–50 nm The compressive strength of high-performance concrete with 3% nS gained 33.25% of the selected characteristic
2019[56] compressive strength of 40 MPa (fck) just in 24 h. At 7 days, the strength exceeded by 13.5% of 40 MPa.
Kumar et al., 2019 Powder 22000 m2/kg The concrete added with 3% nS as a replacement for cement showed higher compressive strength and improved
[37] durability properties. Compared to the reference concrete, the compressive strength of 3% nS increased by 31.42%.
Alhawat et al., Colloidal 15 nm The concrete compressive strength is directly affected by the specific surface area of nS particles. A greater increase
2019[55] in compressive strength is observed at 3% nS of 250 m2/g specific surface area (SSA) compared with nS of 51.4 m2/g
and 500 m2/g SSA. 51.4 m2/g nS particles is observed as least effective in strength improvement. The w/b ratio also
influences the improvement of the strength of nS concrete. The optimum amount of nS replacement was closely
associated with the nS particles’ reactivity and agglomeration level.

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A. P. P., Dheeresh Kumar Nayak, B. Sangoju et al. Construction and Building Materials 278 (2021) 122347

Table 2
The effect of nS on the compressive strength of different types of concrete.

Author Type of Type and Remarks

concrete size of nS
Najigivi et al., Concrete with Powder The compressive strength increased for nS replacement up to 1.5% for 80 nm particles and up to 1% for 15 nm
2010 [60]-I nS 15 nm particles. However, at 2% nS, the strength was still higher than the reference mix.
Najigivi et al., Concrete with Powder The compressive strength of concrete with 80 nm nS declined up to 28 days compared to the concrete with
2010 [60]-II nS 0 nm 15 nm; however, 80 nm nS concrete showed a higher value of compressive strength at 90 days.
w/b = 0.4
Du et al., 2014 Concrete with Powder The concrete specimens with 0.3 and 0.9% nS were tested for compressive strength.The strength increased due
[52] nS 13 nm to the nano-filler effect and pozzolanic activity with an increase in nS content.
Even at small dosages of 0.3 and 0.9% nS, the 28 days compressive strength increased by 9 and 12%,
respectively, relative to the reference concrete.
w/c = 0.49.
Saloma et al., Concrete with Powder As the nS content increased up to 10%, the compressive strength also increased.
2013 [63] nS 10–140 nm The compressive strength of nS concrete increased in the range between 3.82% and 11.84% at the age of 3 days,
but the strength increase ranged from 3.87% to 17.24% and 4.93% to 24.59% at the age of 7 and 28 days,
respectively.
This shows that up to 3 days, the hydration reaction takes place only between cement and water. After 3 days,
nS reacts with free calcium oxide and forms a new cement paste. This indicates that the nS particles influence
to increase the compressive strength after 3 days. w/c = 0.2
Shaikh et al., HVFA (38% FA) Powder By adding 2% nS, the compressive strength of HVFA (38% FA + 2%nS) is increased approximately by 20, 23, and
2014 [54]-I 25 nm 14% at 7, 28, and 90 days respectively. The water to cement ratio used is 0.4.
Shaikh et al., HVFA (58% FA) Powder The compressive strengths of HVFA with 60% FA and HVFA with 58% FA + 2% nS are almost the same for up to
2014 [54]-II 25 nm 90 days. The strengths observed for these samples are less compared to the HVFA with 38% FA + 2%nS. w/c = 0.4
Zhang et al., HVFA (48% FA) Powder 2% NS, 48% fly ash, 50% cement at 0.45 w/c.
2012 [34]-I 12 nm The strength increased by 25,13,18% for 7, 28, and 91 days respectively, compared to the reference mix of 50%
cement and 50% FA.
Zhang et al., High Volume Powder 2% NS, 48% slag, 50% cement at 0.45 w/c.
2012[34]-II slag 12 nm The strength increased by 18,3 and 3% for 7, 28 and 91 days respectively compared to reference mix of 50%
cement and 50% slag. The strength increased by 18,3 and 3% for 7, 28, and 91 days, respectively, compared to
the reference mix of 50% cement and 50% slag. The strength of the ITZ is increased significantly by the low w/c
in the presence of nS, resulting in the high compressive strength. However, the strength is increased to such an
extent that the coarse aggregate becomes the weakest link in concrete, and cracks are formed through the
coarse aggregate. Observation by Varghese et al. [56] confirms this because in their investigations a few cracks
were noted across the aggregate.
This is why the strength of the slag concrete at 2% nS at 28 and 91 days was not further increased.
Singh, L. P et al., FAC Powder Concrete containing 30, 40, and 50% FA and 3% nS tested for compressive strength.
2019[24] The maximum strength was demonstrated by concrete with 30% FA plus 3% nS (30FA3nS).
Compared to the 30FA3nS blend, concrete samples with 30% FA plus 6% SF showed a slight improvement in
strength.
w/b = 0.29.
Nazari et al., GGBFS SCC Powder As nS content increased up to 3%, the compressive strength of concrete containing GGBFS increased.
2011 [70] 15 nm The reduction of the concrete compressive strength at the nS particles more than 3% might be due to the
deficiency of hydrated lime w.r.t the nS particles, which led excess silica to leach out and causing a deficiency in
strength.
w/b = 0.4
Jalal et al., 2015 HPSCC400- Powder Replacing 2% nS in concrete with 400 and 500 kg/m3 binder contents increased compressive strengths by 22,
[43]-I nS2% 15 ± 3 nm 38, and 43% and 22, 56, and 62% respectively at 7, 28, and 90 days.
Jalal et al., 2015 HPSCC400- Powder The replacement of 10% SF and 2% nS in concrete with the same binder content of 400 and 500 kg/m3 improved
[43]-II SF10% nS2% 15 ± 3 nm the compressive strength by 62, 52, and 55% and 30, 67, and 73%, at 7, 28, and 90 days respectively.
Jalal et al., 2015 HPSCC500- Powder w/b = 0.38
[43]-III nS2% 15 ± 3 nm
Jalal et al., 2015 HPSCC500- Powder
[43]-IV SF10% nS2% 15 ± 3 nm
Quercia et al., SCC Powder The compressive strengths observed at 7, 28, and 91 days were 62.8, 78.5, and 91 MPa, respectively, at 3.8% nS
2014 [49]-I dosage. However, for the reference mix, the compressive strengths were 62.3, 78.2, and 83.5 MPa, respectively,
at 7, 28, and 91 days.
w/c = 0.45
Quercia et al., SCC Colloidal The concrete compressive strengths were 65.3, 87.7, and 92.2 MPa, respectively, at 7, 28, and 91 days, with 3.8%
2014 [49]-II nS.
w/c = 0.45
Ghafari et al., UHPC Powder UHPC with SF and 1,2,3, and 4% nS tested for the compressive strength. As the nS content increased up to 3%,
2014 [42] 15 ± 5 nm the compressive strength increased.
w/c = 0.2
R. Yu et al., 2014 UHPC Nano-silica UPHC with 1, 2, 3, 4, and 5% nS dosage tested for compressive strength. The maximum strength was obtained at
[9]-I slurry 4% nS dosage. Adding 2.5% steel fibers to UHPC significantly improved the compressive strength up to 135 MPa
120 (0.12 from 91.3 MPa, which was observed in UHPC without steel fibers at 4% nS and at 28 days.
mm) w/c is 0.4
R. Yu et al., 2014 UHPC Nano-silica
[9]-II With 2.5% slurry
steel fibers 120 (0.12
mm)
Chithra et al., HPC Colloidal The nS content in the HPC with copper slag fine aggregate is varied from 0.5 to 3%. The compressive strength
2016 [65] 5 to 40 nm increased with nS replacement up to 2% and then decreased slightly for higher nS content.
Compared to the reference concrete, an increment of 33.2, 18.2, and 26.8% in compressive strength at 7, 28, and
90 days is achieved by 2% nS replacement. w/b = 0.31
Elrahman et al., LWAC Colloidal Lightweight concrete with 1, 2, and 4 percent nS showed 4, 22, and 26% higher compressive strengths,
2019 [48] <150 nm respectively, than the reference mix after 7 days of curing.
After 28 days of curing, the strength increase was 8, 24, and 31%, respectively, in concrete with 1,2 and 4% nS
dosages. The strength increase, however, was insignificant after 90 days of curing. w/b = 0.4

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A. P. P., Dheeresh Kumar Nayak, B. Sangoju et al. Construction and Building Materials 278 (2021) 122347

High strength concrete (HSC) containing 1.25% macro-polymeric

(MP) fiber and 3% nS showed a 29% increase and concrete contain-
ing 0.1% PP, 0.9% MP and 3% nS showed a 25% increase in strength.
While the HSC containing only 3% nS showed an improvement of
16% tensile strength compared to plain concrete [69].
Compared to the reference concrete, the split tensile strength of
HPC partially replaced with copper slag as fine aggregate exhibited
an increase of 89, 33.2, 18.2, and 26.8% respectively at 1, 7, 28, and
90 days by adding 2% CnS. Whereas at 2.5% CnS, the increase in
strength reduced to 78.5, 29.5, 15.5, and 21.5%, respectively at 1,
7, 28, and 90 days [65].
Kumar et al. [37] reported an improvement of 22% in tensile
strength by replacing OPC with an optimal dose of 3% nS. With
the addition of 1.2% nS particles the split tensile strength of 100%
Fig. 5. Split tensile strength of concrete with 3% nS and 0.4 w/c ratio.
RA concrete reached close to the strength of the control mix with
natural aggregate [87]. Mukharjee et al. [47] observed an increase
and up to 10% exhibited an increase in splitting tensile strength at of split tensile strength in RAC as nS content increased and that the
0.2 w/c ratio [63]. With an increase in nS content up to 3%, the split tensile strength of RAC containing 3% nS was nearly equal to that of
tensile strength of the concrete increased due to reduced voids in control concrete with natural aggregate, and this is because nS
the mortar matrix and the formation of a strong ITZ [45]. The ten- offered a denser and stronger interfacial transition zone (ITZ).
sile strength of the polyethylene terephthalate (PET) composite Quercia et al. [49] also reported that the bond between hardened
concrete was increased by 25% and 48% relative to the reference paste and aggregate strengthened by nS increased the tensile
concrete and PET composite concrete, respectively, by 3% nS inclu- strength in concrete.
sion [59]. The development of tensile strength in nS concrete at the Comparison of the tensile strength of concrete with 3% nS at 0.4
early age was reported slightly high compared to the mS concrete, w/c ratio at 7, 28 and 90 days is given in Fig. 5. Fig. 6 shows 28 days
but both nS and mS concrete exhibited almost the same tensile tensile strength in different concretes at different nS dosages. The
strength at later ages [56]. details of the studies are provided in Table 3.
Compared to the reference concrete at 87 days, the ultimate
tensile strength of concrete containing 1% nS increased by 46%, 3.3. Flexural strength
but the strength improvement was reduced to 28% when 25% FA
with 1% nS were applied [76]. According to Hameed et al. [73], The studies by Jalal et al. [43] reported that the HPSCC contain-
2.5 to 10% CnS in SCC with 10% mS increased the tensile strength ing 2% nS and 10% SF showed higher flexural strength compared to
from 16.67 to 34.87%, respectively, compared to the SCC with control concrete with a maximum increase of 59% at 28 days; how-
10% mS alone. The split tensile strength increased with nS content ever, the rate of developing flexural strength was seen to be
up to 3% in the GGBFS admixed SCC, and further addition of nS decreased at later ages. They further reported that the flexural
caused the strength to decrease, similar to the results of compres- strength of the concrete containing nS alone was comparatively
sive strength [70]. less than that of nS plus SF admixed concrete. According to Naji

Fig. 6. Tensile strength of different types of concrete at different nS dosages and w/b ratios at 28 days.

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A. P. P., Dheeresh Kumar Nayak, B. Sangoju et al. Construction and Building Materials 278 (2021) 122347

Table 3
The effect of nS on tensile strength of different types of concrete.

Reference Type of concrete Type and Remarks

Size of nS
Najigivi et al., 2010 [60]-I Concrete with nS Powder Up to 2 percent inclusion of nS particles increased the splitting tensile strength. The optimal level of
15 nm nS replacement were 1 and 1.5% for 15 (fine nS)and 80 nm (Course nS)particles, respectively.
Najigivi et al., 2010 [60]-II Concrete with nS Powder Compared to reference concrete, an increase of 83 and 72% were noted in tensile strength for fine
80 nm and coarse nS, respectively, in their optimum dosage at 28 days.
72% increase for CN
w/b = 0.4
Saloma et al., 2013 [63] Concrete with nS Powder With an increase in nS particles up to 10%, the splitting tensile strength increased. A strong
10–140 nm correlation between split tensile strength and compressive strength was observed.
w/c = 0.2
Mukharjee et al., 2014, Concrete with nS Colloidal The pozzolanic activity and filler effects of nS particles improved the split tensile strength. Less
2020 [47,45] 8–20 nm voids and strong ITZ contributed high tensile strength to nS added mix.
w/b = 0.4
Kumar et al., 2019 [37] Concrete with nS Powder An optimum dosage of 3% is observed for maximum tensile strength development. Even at a 5% nS
dose, the splitting tensile strength was higher than that of the reference concrete. The
enhancements in splitting tensile strength were due to pozzolanic action and nS particle filler
effects that made the concrete stronger and denser.
w/b = 0.4
Varghese et al., 2019 [56]. Concrete with nS Powder The development of high early age splitting tensile strength in nS concrete was similar to that in
40–50 nm compressive strength. After 28 days, the difference in split tensile strength of nS concrete and mS
concrete was small. An increase of 44%in tensile strength, compared to reference concrete, was
observed in nS concrete with 3% nS.
w/b = 0.4
Sivasankaran et. al., 2019 Concrete with nS Powder An increase of 45 and 32% in divide tensile strength was observed for concrete with 1% nS and
[76] 50 nm concrete with 25% FA plus 1% nS, respectively, on the 29th day.
Sivasankaran et. al., 2019 Concrete with 25% w/b = 0.5
[76] FA + 1% nS
Quercia et al., 2014 [49]-I SCC Powder The average split tensile strengths of concrete with powdered and colloidal nS were 5.48 and
Quercia et al., 2014 [49]-II SCC Colloidal 4.92 N/mm2, respectively, and higher than the tensile strength of 4.51 N/mm2 observed in reference
concrete.
w/b = 0.43
Hameed et al., 2020 [73] SCC Colloidal Compared to reference concrete, an increase of 35% in tensile strength was observed at 28 days in
SCC with 10% nS. w/b = 0.34
Nazari et al., 2011 [70] GGBFS Powder The split tensile strength of GGBFS concrete specimens added with nS particles was more than those
SCC 15 nm of reference specimens, and the tensile strength increased by nS addition up to 3%; however, further
nS addition decreased the tensile strength. An increase of 94% in tensile strength was noticed in
concrete with 3% nS addition at 28 days, compared to reference concrete. w/b = 0.4
Jalal et al., 2015 [43]-I HPSCC500-SF10% Powder Adding 2% nS into HPSCC with 400 kg/m3 binder content increased the tensile strength only 3% at
nS2% 15 ± 3 nm 28 days, compared to the reference mix, but at 90 days, it increased to 13%. However, adding 2% nS
Jalal et al., 2015 [43]-II HPSCC500-nS2% and 10% SF into HPSCC with 400 kg/m3 binder content increased the tensile strength by 33% and
Jalal et al., 2015 [43]-III HPSCC400-nS2% 26%, respectively, compared to the reference mix at 28 and 90 days.
Jalal et al., 2015 [43]-IV HPSCC400-SF10% In the case of 500 kg/m3 binder content HPSCC, adding 2% nS increased the tensile strength 30.5 and
nS2% 26% respectively, at 28 and 90 days. Adding 10% SF with 2% nS into 500 kg/m3 binder content HPSCC
resulted in 33% and 36% increase in tensile strength.
w/b = 0.38
Chithra et al., 2016 [65] HPC Colloidal The dosage of nS ranged from 0 to 3%; however, 2% of the optimal dose of CnS was observed. The
5–40 nm increase in splitting tensile strength varied from 7.7 to 25.4% and 7.5 to 26.5%, respectively, at 28
and 90 days.
w/b = 0.31
Hassan Nataj et al., 2017 Steel-fiber HSC Powder With 1% steel filers and 2% nS, HSC’s splitting tensile strength was improved by 8.2% relative to the
[44] -I 20–30 nm reference mix. The splitting tensile strength was increased by 5.8% in the case of 0.5 percent forta-
Hassan Nataj et al., 2017 Forta-ferro fiber HSC ferro fibres and 3 percent nS.
[44] -II w/b = 0.32
Fallah et al., 2017 [69]-I HSC with 3% nS Powder Adding 3% nS alone into plane concrete increased the tensile strength by 16.60% compared to the
Fallah et al., 2017 [69]-II HSC with 1.25% 20–30 nm reference mix.
MP + 3% nS Incorporating 3% nS in HSC with 1.25% macro polymeric (MP) fibers increased the splitting tensile
Fallah et al., 2017 [69]-III HSC with 0.2% strength from 7.24 MPa to 7.34 MPa. In 0.2% Polypropylene (PP) fiber HSC the tensile strength
PP + 3% nS increased from 6.41 MPa to 6.77 MPa by adding 3% nS. Hybrid reinforced concrete with MP and PP
Fallah et al., 2017 [69]-IV HSC with 0.1% fibers with 3% nS exhibited a strength improvement of 7.1 MPa; however, hybrid HSC without nS
PP + 0.9% MP + 3% nS exhibited a tensile strength of 6.71 MPa.
w/c or w/b = 0.55
Behzadian et al., 2019 [59] Conc./PET Composite Powder The introduction of nS particles into the cement matrix improved the tensile strength. At 3% nS
20–30 nm dosage, a maximum tensile strength of 3.11 MPa was observed. More nucleation sites for pozzolanic
activities and cement hydration were formed in the presence of nS particles, which then led the
hydrated products to precipitate in the concrete voids, forming the dense, homogenous, and
compact concrete microstructure.
w/c = 0.55
Mukharjee et al., 2014 RAC Powder The split tensile strength of RAC with 3% nS was close to its value of control concrete. The pozzolanic
[47] 8–20 nm effect and filler effects of n are responsible for this split tensile strength enhancement.
w/c = 0.4
Younis et al., 2018 [87]-I RAC Powder For RAC with 50% recycled coarse aggregate, the maximum splitting tensile strength of 3.74 MPa
50% RA + 0.8% nS 20–30 nm was obtained at 0.8% nS. For 100% replacement of recycled aggregate, the maximum tensile strength
Younis et al., 2018 [87] -II RAC100%RA + 1.2% of 3.58 MPa was obtained at 1.2% nS. The split tensile strength observed for 100% natural aggregate
nS concrete was 3.65 MPa.
w/c = 0.48

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A. P. P., Dheeresh Kumar Nayak, B. Sangoju et al. Construction and Building Materials 278 (2021) 122347

Givi et al. [60], nS particles enhanced the flexural strength at all of nS concrete is greater than the non-nS concrete. According to
stages of curing up to 90 days without much variations in the rate Durgun et al. [88], the increase in stiffness was associated with
of strength development. The study further identified that at the efficient densification of the interface between the aggregates
90 days, concrete containing nS with 80 nm diameter exhibited a and the hardened cement matrix by the addition of nS, resulting
higher flexural strength compared to concrete with 15 nm dia. in a stronger bond between them. The latest research showed only
nanoparticles. The flexural strength declined by incorporating the slightest increase in the elastic modulus of concrete while add-
PET particles in the composite concrete was improved by nS parti- ing the nS particles up to 3% [45]. However, Belkowitz et al. [61]
cles due to the improved adhesion between the contact area of the observed a higher elastic modulus in concrete with smaller
cement paste and aggregate, as reported by Behzadian et al. [59]. (5 nm) nS particles at lower doses and with larger (16 and
Elrahman et al. [48] observed an improvement of early flexural 46 nm) particles at higher doses. Belkowitz’s study also showed
strength in LWAC, with a limited improvement noticed for a lower that the smallest particles of 5 nm nS at its lowest dosage gener-
dose of nS; however, nS dosage above 1% effectively enhanced the ated the highest modulus, which is a 20% increase over OPC and
flexural strength at 28 days. Naji Givi et al. [78] noticed that the 22% over concrete with 20% FA, indicating that the size of the nS
flexural strength of the water-cured specimens increased with and its surface area are sensitive to the mechanical properties of
the substitution of up to 1% nS, and then decreased as nS increased, the concrete. Other investigation on FA concrete [76] showed that
however, in the specimens cured in the solution of lime the flexural incorporating 2% nS increased the elastic modulus of FA (25% of
strength was improved for nS up to 2% replacement. According to cement as replacement) concrete by 134% on 87th day, but for con-
Mukharjee et al. [47], the addition of 3% nS into RAC compensated crete containing only nS, the increment was 167% compared to the
for the decline in the flexural tensile strength as a result of the reference concrete. It is interesting to note that the elastic modulus
replacement of natural aggregate (NA) with recycled aggregate of the concrete with 25% FA alone on 87th day and for concrete
(RA) and a 15% increase in flexural tensile strength at 28 days with 2% nS plus 25% FA on 29th day was the same [76]. Hasan-
was also observed in both NA and RA concretes due to nS addition. Nattaj et al. [44] reported that due to the increased compactness
According to Li et al. [38], compared to the control UHPC matrix, of the bond between cement paste and aggregates, as reported
adding 1% nS exhibited approximately 41 and 35% higher flexural by [63], the nS and SF in the fibre reinforced concrete (FRC)
strength for UHPC under the combined curing conditions of 2 days improved the elastic modulus. Mukharjee et al. [45] reported an
heat and 26 days of standard curing, at 0.16 and 0.17 w/b ratios, improvement in concrete density by adding nS relative to the ref-
respectively. Adding more than 1% nS, however, resulted in a lesser erence mix, showing the compactness of the nS added concrete.
flexural strength improvement. The studies conducted on SCC with colloidal nS, the optimum elas-
Fig. 7 shows the effect of nS with its different dosages at 28 days tic modulus was reached at 2.5% CnS content [73]. Fallah et.al. [69]
on the flexural strength of various concrete samples. The findings reported a significant influence of nS on initial and secant modulus
on the effect of nS on flexural strength in concrete are summarised of elasticity of HSC, and at 2% nS, the modulus of elasticity reached
in Table 4. its maximum value. Erdem et al. 2018 [86] reported an increase in
dynamic elastic modulus in RAC, due to improved microstructure,
with an increase in the amount of nS.
3.4. Modulus of elasticity
The effect of nS at 28 days on the elastic modulus of different
types of concretes is shown in Fig. 8. Table 5 summarises the
Saloma et al. [63] observed a higher elastic modulus in nS con-
results on the influence of nS on the elastic modulus of concrete.
crete compared to the non-nS concrete, indicating that the stiffness

Fig. 7. Flexural strength of different types of concrete at different nS dosages and w/b ratios at 28 days.

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A. P. P., Dheeresh Kumar Nayak, B. Sangoju et al. Construction and Building Materials 278 (2021) 122347

Table 4
The effect of nS on flexural strength of different types of concrete.

Author Type of Type and Remarks

concrete size of nS
Najigivi et al., 2010 [60]-I Concrete Powder Up to 2 percent inclusion of nS particles increased the flexural strength. The optimal level of nS
with nS 15 nm replacement were 1 and 2% for 15 and 80 nm particles, respectively.
Najigivi et al., 2010 [60]-II Powder w/b = 0.4
80 nm
Najigivi et al., 2010 [78]-I Concrete Powder Ord.Conc., cured in lime solution
with nS 15 ± 3 nm Similar to the compressive strength, the flexure strength of the samples cured in lime solution was
higher compared to water cured samples [60]. The optimum dose of nS was 1% to improve the
mechanical properties of the water cured samples, while that was 2% for lime cured samples. In the
presence of lime solution, the formation of CSH gel was higher as the amount of nS present was close to
the amount needed to combine with liberated lime during the hydration process, resulting in less
leaching of silica compared to water cured samples. w/c = 0.4
Varghese et al., 2019 [56] HPC Powder The flexural strength is influenced by the compactness of ITZ obtained by the application of nS particles.
25 nm At all ages, the flexural strength of nS-HPC surpassed that of both mS-HPC and reference concrete,
indicating that nS particles strengthen the ITZ.w/c = 0.4
Jalal et al., 2015 [43]-I HPSCC400- Powder Cement replacement by 10% SF plus 2% NS improved the flexural strength for binder content of 400 and
nS2% 15 ± 3 500 by 23.5, 58.9 and 47% and 20, 52 and 52% respectively at 7, 28 and 90 days compared to control
Jalal et al., 2015 [43]-II HPSCC400- specimens.
SF10% Water binder ratio (w/b) = 0.38
nS2%
Jalal et al., 2015 [43]-III HPSCC500-
nS2%
Jalal et al., 2015 [43]-IV HPSCC500-
SF10%
nS2%
Nazari et al., 2011 [70] GGBFS SCC Powder GGBFS SCC flexural strength increased by incorporating up to 3% nS particles.
15 nm The flexural strength was high compared to the reference concrete for all nS incorporated concrete due
to the increased formation of hydration product in the presence of nS nanoparticles.
w/b = 0.4
Chithra et al., 2016 [65] HPC Colloidal Compared to reference concrete, the improvement of flexural strength at 7 days was 11.7, 20.1, 29.3,
5 to 40 nm 37.7, 33.2 and 27.6% for 0.5, 1, 1.5, 2, 2.5 and 3% nS respectively and at 28 days the improvement was
10.7, 21.1, 28.8, 36.5, 29.2 and 22% respectively.w/b = 0.31
Li et al., 2015 [38]-I UHPC Powder Standard curing.
20 nm Maximum flexural strength obtained at 1% nS.
Two w/b ratios 0.16, 0.17 were used.
The specimen at 0.16 w/b showed max. flexural strength of 25.8 MPa, however at 0.17 w/b the strength
decreased to 23.7 at 28 days.
w/b = 0.16
Li et al., 2015 [38]-II UHPC Powder Combined curing, first two days of heat curing in a lime bath at 90 °C + 26 days of standard curing.
20 nm placed into a lime bath at 90 °C)
Maximum flexural strength obtained at 1% nS.
Two w/b ratios 0.16, 0.17 were used.
The specimen at 0.16 w/b showed max. flexural strength of 32.5 MPa, however at 0.17 w/b the strength
decreased to 29.8 at 28 days.
w/b = 0.16
R. Yu et al., 2014 [9]-I UHPC Nano-silica The flexural strength of UHPC was increased from 10.4 MPa (for reference concrete) to 14 MPa at
R. Yu et al., 2014 [9]-II UHPC slurry 28 days by incorporating 4% nS. However, this value decreased to 13.2 MPa at a 5% dose of nS particles.
With 2.5% 120 (0.12 By adding 2.5% of steel fibers with 4% nS, the flexural strength of UHPC was increased approximately to
steel fibers mm) 25 MPa at 28 days.
w/c = 0.40
Mukharjee et al., 2014 [47] NAC Colloidal With the addition of 3% nS, flexural tensile strength (FTS) of concrete with natural aggregate (NAC)
Mukharjee et al., 2014 [47] RAC 8–20 nm increased from 4.33 to 4.97 MPa at 28 days. In the recycled aggregate concrete, the FTS increased from
3.96 to 4.54 MPa by applying 3% nS.
The bond between cement mortar and aggregate in ITZ became stronger by adding nS owing to the
pozzolanic products formed by the nS
w/c = 0.40
Elrahman et al. 2019[48] LWAC Colloidal The 28 day flexural strength was effectively enhanced by nS applied at a dose of more than 1% However,
<150 nm further improvement in strength was not found after 90 days.
w/b = 0.4
Behzadian et al., 2019 [59] Concrete Powdered The inclusion of the PET particles into the composite of the concrete decreased its flexural strength, but
with PET 20–30 nm the addition of nS particles improved the strength.
w/b = 0.55

3.5. Abrasion resistance use of nS up to 2% in high-performance slag concrete (HPSC),

whereas a slight decrease in abrasion resistance observed at 2.5
Nazari et al. [79] reported that replacing Portland cement with and 3% nS. For the concrete containing 1% nS, the surface and side
nS particles up to 2 wt% increased the resistance of abrasion of the indices of abrasion resistance increased by 157% and 139%, respec-
concrete, and a higher rate of increment was seen for the higher tively [62]. Shamsai et al. [89] observed the influence of w/c ratio
dose of nS for both water and lime water cured specimens. Chithra on abrasion resistance in nS concrete and recorded a 36% increase
et al. [65] also noted that the abrasion resistance increased by the in abrasive strength when the w/c ratio decreased from 0.50 to

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A. P. P., Dheeresh Kumar Nayak, B. Sangoju et al. Construction and Building Materials 278 (2021) 122347

Table 5
The effect of nS on elastic modulus of different types of concrete.

Reference Concrete Type and Remarks

size of nS
Saloma et. al., Concrete Powder The average elastic modulus of
2013 [63] with nS 10– concrete with nS was observed
140 nm greater than that of concrete
without nS. Due to the improved
compactness of cement paste-
aggregate bond in nS concrete,
compared to concrete without
nS, the nS concrete had a higher
stiffness.
Durgun et al., SCC Colloidal Among 5, 17, 35 nm nS particles.
2018 [88] 5,17,35 nm 35 nm size particles showed
effective in improving the
elastic modulus in concrete with
FA.
Mukharjee Concrete Colloidal With the addition of 3% nS, the
et al., 2020 with nS 8–20 nm change in elasticity modulus (E)
[45] was not significant as it showed
only a 4% increase in E
compared to the reference mix.
Sivasankaran Concrete Powder By adding 2% nS, the elastic
et al., 2019 with nS. 50 nm modulus was enhanced in all
[76] nS + 25% concrete mixes in which the FA
Fig. 8. Elastic modulus of different types of concrete at different nS dosages at Fly ash content ranged from 25 to 75
28 days. conc. percent, as well as in concrete
without FA.
At 29 days, the increase in
elastic modulus was not
significant, but at 87 days, it was
0.33. Cheng et al. [90] reported a reduction in abrasion loss of nS
increased by 167% for concrete
concrete compared to non-nS concrete by 36.4, 39.1, 44.4% for 7, with 2% nS without FA and by
28, and 84 days, respectively. 167, 134,127% for concrete with
2% nS and 25, 50, and 75% FA
content, respectively.
3.6. Impact resistance Hasan-Nattaj 1% Steel Powder nS in concrete reinforced with
et al., 2017 Fiber + 3% 20–30 nm steel and forta-ferro fibers
Erdem et al. [86] reported that the addition of nS to the RAC [44] nS increased the elastic modulus,
increased its impact resistance. Though the number of blows for 0.5% Forta- with the increase was more
ferro significant for steel fibers.
the formation of the first crack did not correlate to the amount of
fiber + 3% Incorporating nS particles
nS added, the number of blows for the ultimate failure increased nS resulted in an increase in the
as the nS content increased. According to the Erdem et al. this is compactness of the cement
due to the reduced pores in concrete with enhanced pore structure paste-aggregates bond, which in
at its microscopic level by the application of nS and the consequent turn increased the stiffness of
the concrete, thus improving the
stimulation of the toughening mechanism and crack deflection. elastic modulus.
Hameed Colloidal The addition of CnS produces a
3.7. Compressive stress strain behaviour/ stress strain relationship et al., 2020 small increase in the elastic
[73] modulus relative to reference
concrete. Maximum elastic
According to Fallah-Valukolaee et al. [91], adding nS to the modulus was observed at 2.5%
hybrid fiber-concrete contributed to an increase in the ultimate CnS dosage; however, the
strain. The study reported that the strain at peak stress increased maximum compressive strength
was observed at 10% nS
in the fiber-reinforced concrete with nS compared to that in the
Fallah et al., 1.25% Powder By using the nS partcles as a
concrete lacking nS. The study also concluded that the effect of 2017 [69] MP + 3% nS 20–30 nm cement replacement, the elastic
nS on the ultimate strain was more significant than that of SF in modulus of concrete increased
synthetic fibre reinforced concrete. relative to the plain concrete.
Nematzadeh et al. [92] reported that the use of nS resulted in a With 2% nS the high strength
concrete with PP and MP fibers
lower strain at peak stress in the steel fiber-reinforced concrete
exhibited high initial and secant
compared to the non-nS steel-fiber reinforced concrete, whereas modulus of elasticity.
this effect of nS was negligible in forta-ferro fiber-reinforced con- 0.2%
crete. In the above investigation, it was also revealed that the PP + 3%nS3
incorporation of nS into the FRC improved its ultimate strain, with 0.1%
PP + 0.9%
higher ultimate strains for higher nS replacement rates. Also, for MP + 3%nS
both steel and forta-ferro FRCs, as the replacement rates of nS
increased, the concrete carried greater normalized stress at a par-
ticular strain, resulting in a higher area under the stress–strain
3.8. Non-destructive parameters
curve.
As the compressive strength increased by the use of nS and/or
According to Mukharjee et al. [45], the ultrasonic pulse velocity
mS in concrete, the axial stress–strain curve became steeper at
(UPV) and rebound number (RN) values increased in the concrete
both the pre-peak and post-peak stages, indicating higher stiffness
mix with an increase in the nS content, indicating that the concrete
and lower ductility [93].
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A. P. P., Dheeresh Kumar Nayak, B. Sangoju et al. Construction and Building Materials 278 (2021) 122347

quality ameliorated from good to excellent with the addition of nS content and subsequent development of more pores in hardened
particles. concrete. According to Atmaca et al. [67], the sorptivity of 3% nS
HSLWC decreased by 25% compared to the reference concrete with
the same replacement level of LWA. As reported by Elrahman et al.
4. Effect of nano-silica on durability parameters
[48] 4% nS showed a beneficial effect on LWC to reduce porosity
and water absorption. The presence of nS found to have reduced
4.1. Pore structure/porosity
the water absorption in hardened high strength concrete with
macro-polymeric (MP) and polypropylene (PP) fibers and the least
Several researchers noted a significant reduction in porosity and
value of absor ption was observed at 3% nS [69]. Younis et al. [87],
improvement in the concrete pore structure while applying nS to
observed that in RAC the water absorption decreased by 11% at a
concrete. According to Zhang et al. [41], the large capillary porosity
small nS dosage of 0.8% compared to control concrete.
decreased with the increased dosage of nS as well as the threshold,
An investigation by Isfahani et al. [82] revealed that 0.5% nS, as a
and critical diameters of the pores were found to have decreased at
cement replacement, had a negligible effect on water absorption
2% nS. Said et al. [84] reported that due to the filling and high poz-
and sorptivity in concrete with 0.65 w/b ratioß however, they were
zolanic actions of nS particles, the threshold pore diameter was
found clearly reducing at 0.55 w/b ratio with 1% nS. Kumar et al.
reduced with a corresponding increase in the percentage of small
[37] reported a 36.84% decrease in water absorption in concrete
pores (micro-cracks) in concrete with and without FA, which was
added with 3% nS compared to the normal concrete, stating that
significant at 6% dosage of nS compared to 2%. The addition of nS
the highly reactive nS formed more CSH gel and packed the voids
significantly reduced the increased pore size and total porosity
of the concrete matrix.
resulting from the replacement of cement by FA [83].
The permeability decreased with an increased nS dosage and
Ghafari et al. [42] reported that the pore structure was refined
the maximum reduction of 51.5% in permeability compared to
in UHPC due to the pores being filled by the additional hydration
the control mix reached at 4.5% nS [64]. Erdem et al. [86] also
products resulting from the high pozzolanic reactivity of silica
reported a similar effect of nS in RAC as the nS in concrete
nanoparticles. According to Sivasankaran et al. [76], the inclusion
improved its porous structure. Rezania et al. [94] reported that
of 2% nS reduced the porosity in the cement paste by filling the
the permeability reduction experienced a decreasing trend with
micropores and thus increased the pore size distribution.
the increase in nanoparticle content due to the difficulty of their
Alhawat et al. [55] found that the volume of pores in concrete
dispersion in concrete at their higher dosage. In alkali-activated
containing nS with small surface area (bigger particles) was rela-
slag (AAS) concrete, the use of nS contributed to an undesirable rise
tively high as they were prevented from occupying the pores; how-
in water penetration depths; however, the use of mS reduced the
ever, the concrete containing 3% of nS with large surface area
permeability [95].
(smaller particles) exhibited a more densified concrete microstruc-
Compared to concrete containing nS, the decrease in water
ture rich with CSH and remarkably less capillary pores. Belkowitz
absorption in fiber reinforced concrete with SF was more notice-
et al. [61] stated that the agglomeration of the small particles of
able, according to Hasan-Nattaj et al. [44]. The result obtained by
nS caused voids to form in concrete at their high dosage, resulting
Jalal et al. [43], on the other hand, showed that water absorption
in high concrete porosity.
in HPSCC was further reduced by the inclusion of 2% nS with 10%
Du et al. [77] reported that the porosity of the LWC with 1% nS
SF due to the efficient packing and refinement of concrete micro
was reduced due to a more compact and homogeneous microstruc-
and pore structures achieved through the combined effect of nS
ture developed by the filler effect and pozzolanic action of the nS
and SF. Due to its more refined pore structure, water absorption
particles. According to Du et al. however, more than 1% nS, which
in concrete with nS was reduced by 6.4% and 18.3% compared to
increased the viscosity of the cement paste, allowed more air voids
concrete with mS and reference concrete [96].
to entrap into the concrete mixture during mixing, and the poros-
Najigivi et al. [97] reported that rice husk ash (RHA) mixed con-
ity of the hardened concrete could be increased if the densifying
crete with 15 nm nS significantly enhanced water absorption resis-
effect of the nS particle is not sufficient to compensate for this
tance at 28 days; however, after 90 days, a higher resistance was
increased air content. However, Elrahman et al. [48] reported that
observed in concrete with 80 nm nS. Tawfik et al. [98] found a low-
due to the increased solid content between the voids, replacement
est water penetration in HPC consist of 3% nS compared to the HPC
of 4 wt% nS in LWC reduced the pore diameter and the volume of
incorporated with nanoparticles of silica fume, fly ash or coal.
porosity to 39.53 vol% from 54.38 vol% of the reference concrete.
Mohammed et al. [99] reported that the nS particles induced fly
The nS particles improved the pore structure of SCC and increased
ash reaction and decreased the roughness of the inner surface of
the content of all mesopores and macropores [70].
the voids, which in turn caused an increase in infiltration in the
pervious concrete. For a good pervious concrete, it is favourable
4.2. Water absorption, sorptivity, water permeability and infiltration to have a better infiltration rate.
rate Water absorption of different types of concrete added with nS is
illustrated in Fig. 9. The particulars of water absorption of nS added
Ghafari et al. [42] reported that adding nS resulted in reduced concrete is given in Table 6.
absorption of water and sorptivity in UHPC relative to the refer-
ence concrete mix, indicating that the connection between the cap- 4.3. Chloride ion penetration
illary pores was significantly reduced due to the pores filled with
the additional hydration products formed by high pozzolanic reac- Mercury intrusion porosimetry (MIP) tests results confirmed
tivity of nS. This was similar to the findings of Du et al. [77], who that the filler and pozzolanic actions of nS reduced the rate of
observed a 35% reduction in the initial setting time and 32% in sec- water and chloride ion penetration even at a low dose of 0.3% nS
ondary sorptivity in pure cement LWC by using 2% nS, an optimum [52]. A similar observation was made by Isfahani et al. [82] showed
dose for pure cement, as additive. However, the initial and final that the chloride diffusion coefficient reduced at 0.5% nS dosage
sorptivity again reduced to 73 and 83% respectively in slag cement with w/b ratios of 0.55 and 0.65; however, at a higher dosage of
LWC by the use of 1% nS, an optimum dose for slag cement, as addi- nS, such reduction was not noticed. The reduction of charge passed
tive and which could be attributed to the insufficient densifying within the slag concrete was found to be in agreement with the
effect of nS at its higher dosage to compensate the increased air reduction in the critical threshold diameter of pores and refined
13
A. P. P., Dheeresh Kumar Nayak, B. Sangoju et al. Construction and Building Materials 278 (2021) 122347

to sulphate attack [98]. This indicates that the nS particles are very
effective in resisting sulphate attack in concrete.

4.5. Carbonation

According to Singh et al. [24], the use of 3% nS in FA concrete

significantly reduced depth of carbonation by 73% after 180 days
of exposure in comparison with its control mix, while FA concrete
with SF showed a reduction of only 35% in the same exposure con-
dition. It is due to the hydration products produced in the presence
of nS are more stable and resistant to the penetration of aggressive
ions, which would benefit the more extended durability of FA con-
crete. Kumar et al. [37] reported that inclusion of nS up to 3%
decreased the carbonation depth by 46 and 17% at 7 and 70 days,
respectively, compared to ordinary concrete, whereas a further
increase of nS increased the carbonation depth with the time of
exposure. The authors hypothesized that this is due to the excess
CH reacted with nS to form CSH gel, and at a 3% dose of nS, a dense
matrix was obtained, and further addition of nS did not contribute
to making a denser concrete.
Fig. 9. Water absorption of different types of concrete at different nS dosages at
28 days. While Isfahani et al. [82] reported that the addition of nS
resulted in detrimental effect on carbonation as the carbonation
microstructure due to the inclusion of nS [34]. Although the poros- coefficient was observed increasing from the reference of 24 to
p
ity was higher in LWC at 2% nS, the higher binding capacity of CSH 29.3 mm/ year at 1% nS for 0.65 w/b ratio, however for 0.55 w/b
gel formed interrupted the chloride ion transport [77]. The reduced ratio with the same amount of nS the carbonation coefficient was
p
conductivity in concrete with a small dose of nS resulted in lower reduced from the reference of 20.4 to 16 mm/ year. Also, accord-
chloride ion penetration in the cementitious matrix [84]. ing to Behfarnia et al [95], due to increased CO2 penetration, the
The resistance to penetration of chloride ions in the nS concrete inclusion of nS particles in AAS concrete caused an increase in car-
was relatively high compared to mS and reference concretes [96]. bonation depth.
However, Jalal et al. [43] revealed that using nS and SF together
in HPSCC reduced chloride ion penetration significantly.
4.6. Corrosion resistance

4.4. Sulphate attack Compared to the other nanoparticles, nS with a 3% optimum

level was found to have improved the durability and reduced cor-
The concrete specimens with 3% nS immersed in sewage water rosion rate in HPC. The depth of corrosion was reduced by 37.8,
for 90 days showed a lowest reduction in compressive strength due 58.5 and 67.5% at 3 months for the HPC incorporated with 1, 2

Table 6
The effect of nS on water absorption in different types of concrete.

Reference Type of concrete Type and size of nS Remarks

Najigivi et al., 2012 [97] Fine nS RHAC 15 nm Powder At 2% nS, the lowest WA of 2.08% was observed in concrete with 80 nm at 90 days.
15 nm Concrete containing 80 nm nanoparticles showed improved water absorption resistance
Najigivi et al., 2012 [97] Course nS RHAC Powder after 90 days of curing, while 15 nm nanoparticles showed improved resistance to
80 nm 80 nm concrete water absorption after 28 days of curing.
Lincy et al., 2017 [96] Colloidal Concrete with nS particles exhibited the lowest water absorption compared to micro
40–50 nm silica (mS) and reference concretes by 6.4% and 18.3%, respectively.
Mukharjee et al., 2020 [45] Concrete with nS Colloidal The WA of the concrete was reduced with the increase in nS content owing to the
–20 nm reduced voids in the concrete by the presence of nS particles. The water absorbing
potential of the concrete mix was consequently reduced.
Nazari et al., 2011 [70] GGBFS SCC Powder Compared to GGBFS concrete with nS particles, the WA in GGBFS concrete without nS
15 nm showed a lower WA at 7 days. However, at 28 and 90 days, the water absorption was
lower for GGBFS with nS particles. This can be attributed to high formation of hydration
products in nS added GGBFS concrete during early age curing.
Chithra et al., 2016 [65] HPC with copper Colloidal Due to the combined action of the pore filling effect and acceleration of hydration of nS
slag as fine 5 to 40 nm the water absorption and sorptivity values of HPSC decreased with an increase in nS
aggregate particles, making the concrete more dense and compact. Maximum decreases in water
absorption and sorptivity values were observed with 2% nS in HPSC.
Younis et al., 2018 [87] RAC Powder The effect of adding 0.4% of nanoparticles to the WA was negligible for both RA contents
RA50% nS1.2% 20–30 nm (50% and 100%), while adding 0.8% of nS contributed to a decrease of 10 and 11% in the
RAC WA of RAC mixes with 50 and 100% RA contents, respectively.
RA100%
nS1.2%
Du et al., 2014 [52] Concrete with nS. Powder Due to the refined pore structure and decreased connectivity of capillary pores in nS
13 nm incorporated mixes the rate of WA in the concrete was reduced. The nS slightly modified
the initial water sorptivity, water absorption and water accessible porosity.
Kumar et al., 2019 [37] Concrete with nS. Powder With surface The minimum WA, 6 and 5.6% respectively at 28 and 90 days, was found in concrete with
area of 22000 m2/kg 3% nS particles. This is 37% less than the WA of control concrete.
Ghafari et al., 2014 [42] UHPC Powder Incorporating 1, 2, 3, and 4% nS into concrete resulted in a decrease of WA by 8.5, 21, 33,
15 ± 5 nm and 29%, respectively.

14
A. P. P., Dheeresh Kumar Nayak, B. Sangoju et al. Construction and Building Materials 278 (2021) 122347

and 3% nS compared to the control sample and a similar trend was pared to the lower nS replacement level also led to a greater crush-
also observed after 6 months [98]. ing load loss to the weight loss ratio.

4.7. Temperature effects

5. Fracture behaviour
Elkady et al. [64] reported an initial compressive strength loss
Fracture behaviour of the concrete is characterized by the
of approximately 30, 16, 25 and 22% in the indirect fire test at tem-
parameters such as fracture energy, fracture toughness, fracture
peratures between 0 °C and 400 °C at 0, 1.5, 3 and 4.5% nS respec-
process zone and critical effective crack-tip opening displacement
tively. However, these losses were 49, 27, 37 and 62% for the
[102]. The fracture energy (Gf) increased as the colloidal nS content
temperature range between 400 °C and 600 °C. In the temperature
increased up to 3%, then decreased for further addition of colloidal
range between 0 °C and 400 °C, the specimen was found to have
nS [103] in self-compacting semi-lightweight (SCSL) concrete and
lost approximately 37, 29, 49, and 26% of its initial bond strength
the sample with less w/b ratio displayed higher fracture energy.
respectively at 0, 1.5, 3, and 4.5% nS dosages. While in the temper-
It was reported that the fracture energy increased as compressive
ature between 400 °C and 600 °C, the above respective losses were
strength increased. The fracture toughness (KIC) of SCSL concrete
approximately 84, 65, 79, and 86%. The study cited that initial loss
increased as nS increased up to 3% and then decreased as in the
of strength at the temperature between 0 °C and 400 °C was due to
case of fracture energy, and KIC increased by 24% as w/b ratio
loss of cohesive force between the layers of CSH gel, while the loss
decreased from 0.45 to 0.35. The fracture process zone (FPZ) was
of strength at the higher temperature, i.e. between 400 °C and
also influenced by the content of the colloidal nS and water binder
600 °C, was attributed to the severe vapour pressure developed
ratio. The FPZ length (Cf) increased as nS content up to 3% and then
in the dense pores of the concrete which caused the spalling and
decreased. However, the Cf decreased by 26% while the w/b ratio
cracking of the concrete.
increased from 0.35 to 0.45 [103]. However, Zhang et al. 2015
The thermogravimetric investigation by [70] in the range of
[104] reported that the fracture parameters increased as the nS
110–650 °C showed dehydration of the hydrated products and
content increased up to 5% and then began to decrease upon fur-
increased loss of weight, after 90 days of curing, of the specimens
ther addition of nS in the fly ash concrete composite.
with nS particles upto 3% in GGBFS incorporated SSC. The spalling
and mass loss experienced in nS admixed HSC when the specimen
heated more than 400 °C, but this was observed just above 300 °C 6. Rate of hydration
for HSC without nS [85].
The temperature variation of the concrete mixes measured by
4.8. Frost resistance the maturity logger for 24 h after mixing showed a noticeable rise
in temperature in nano-silica high-performance concrete (nS-HPC)
Experimental studies of Cheng et al. [90] in cold regions of compared to ordinary concrete and micro-silica high-performance
China showed that applying nS to concrete improved the frost concrete (mS-HPC), indicating that nS particles increased early
resistance of bridge deck pavement. The concrete mass loss rate hydration in concrete. The peak increase of temperature in nS-
in nS concrete was lower than in non-nS concrete for up to 300 HPC was due to the formation of CSH gel by hydration of tricalcium
freeze–thaw cycles, and the loss rate decreased with an increase silicate (C3S) 4 to 5 h earlier than that in ordinary concrete and mS-
in cycles in both non-chloride salt and chloride salt environments. HPC [56]. It was also reported by [41] that compared to SF, nS with
Similarly, according to Cheng et al., the dynamic elastic modulus in its mean particle size of 7 and 12 nm was found more effectual in
nS applied concrete was also high and increased with an increase increasing the hydration rate and reaction in high-volume slag
in the freeze–thaw cycle. Massana et al. [74] also noted an cement (HVSC) concrete.
enhancement in freeze–thaw resistance in HPSCC with nS. Zhang et al. [41] observed that the dormant time in the cement
and the slag pastes was shortened by adding nS, and the hydration
4.9. Effect of acid exposure rate of high-volume slag cement paste was accelerated. The hydra-
tion acceleration of cement could be due to an increase in nucle-
The compressive strength of the nS incorporated specimen ation sites offered by the small particles of nS, and that of slag
exposed to sulfuric acid rain showed a higher compressive strength could be due to an increase in the formation of CH at an early
compared to the reference specimen. This is due to the reduced age owing to the increased cement hydration [34,41]. The rise in
porosity in the concrete by the filling effect of nS and the improved nucleation sites and the increase of pozzolanic activity by adding
bonding between aggregates and hydrated cement paste in the nS increased the hydration heat in HVFA concrete [53,83]. Said
presence of nS [100]. The study also found that the percentage of et al.[84] stated that the ultra-fine nature of the nS was the reason
weight loss of concrete specimens decreased with increased nS for accelerating the hydration reaction kinetics in concrete. Nano-
content in acid exposure. The electrical resistance of concrete spec- silica particles can serve as the nucleus in CSH gel to bind particles
imens also increased by adding more nS due to the high concrete of CSH gel structures tightly, and thus can improve the consolida-
compactness and pore solution composition change. tion and stability of the structure of the hydration products [96].
However, according to [101], compared to the use of nS, SF in Naji Givi et al. [60] reported that the concrete with 15 nm nS par-
high-strength forta-ferro fiber (HSFF) concrete resulted in greater ticles had more CSH gel formed compared to 80 nm particles, at the
improvements in the durability of specimens exposed to the acid initial days of curing, due to more nucleation sites offered by small
environment. The HSFF concrete specimen with 2% nS exhibited particles of nS and subsequent hydration acceleration. However, on
a high reduction in ultrasonic pulse velocity (UPV) compared to contrary to the above findings, Belkowitz et al. [61] mentioned that
the 10% SF incorporated specimens, during its immersion in sulfu- the larger nS particles of low surface area increased the tempera-
ric acid up to 63 days. Furthermore, the above study showed a ture of the hydrating cement more compared to the smaller nS par-
lower weight loss of the specimens, indicating less erosion in the ticles with the higher surface area, suggesting that the greater
acid exposure, with a high replacement level of 10% SF relative to stability and higher effectiveness of the larger nS particles which
the low replacement level of 2% nS. This is due to the lower poten- are less prone to agglomeration compared to the smaller ones.
tial of gypsum and ettringite production in the concrete specimens Du et al. [77] reported that adding 2% nS in slag cement paste
containing 10% silica fume. The higher SF replacement level com- did not further increase the overall heat after 72 h compared to
15
A. P. P., Dheeresh Kumar Nayak, B. Sangoju et al. Construction and Building Materials 278 (2021) 122347

the slag cement paste added with 1% nS. According to Ghafari et al. environment as 2%, and the best dispersion quality was achieved
[42], incorporating nS particles into the cement paste containing by colloidal nS with 20 nm particle size among the particles size
very low w/c can enhance the formation of the hydration products ranged from 5 to 75 nm. However, Belkowitz et al. [61] observed
and thus reduce the volume of portlandite. that the larger nS particles (46 nm size) with low surface area
increased the hydration temperature compared to the smaller nS
particles (5 and 16 nm) of higher surface area. It may be due to
7. Microstructure
the high susceptibility of small particles of nS to agglomeration
due to their higher surface energy [107]. Esmaeil et al. [58] stated
Nano-silica has a very high reactivity owing to its very high sur-
that because of the high surface area of the nS particles and their
face area, and therefore, it reacts quickly with CH crystal and pro-
high reactivity, the lower w/c ratio might also induce uneven dis-
duces CSH gel [105]. Du et al. [52] reported that the ITZ of the
persion of the nanoparticles and their agglomeration in specific
concrete became less porous and more homogeneous even at a
parts of the concrete mix. The colloidal nS with an average particle
small dose of nS, due to its filler effect and pozzolanic action. The
size of 35 nm exhibited the best efficiency with respect to the
studies in LWC also showed that the ITZ between cement paste
mechanical and elastic properties of the SCC [88]. When the aver-
and lightweight aggregates was denser due to the better solid
age particle size of colloidal nS decreased, the strength and elastic
packing and the pozzolanic reaction of nS [77]. It can be further
modulus decreased as well.
explained as the efficiency of nS to react with CH crystals and
The quality of the dispersion nS particles is the most important
reduce their size and quantity effectively, leading to a denser ITZ
parameter which influences and controls the characteristics of nS
microstructure between cement paste and aggregates [42]. A
added concrete [107]. The use of nS as received from the manufac-
reduction in the amount of portlandite, a mineral detrimental to
turer can result in an unpredictable effect in properties of concrete
concrete strength, was also observed in UHPC with 3% nS by
depending on the level of their agglomeration [46]. According to
[42]. Quercia et al. [49] also reported a compacted homogeneous
Mohamed [108], wet mixing of nS particles was more effective
microstructure of small size CSH gel, resulting in formation of a
than mixing them in dry conditions with concrete ingredients to
denser ITZ in SCC. Durgun et al. [88] reported that the ITZ no longer
contribute to mechanical properties, attributed to the uniform dis-
existed between aggregates and the hardened cement matrix in
persion of the nanoparticles in the mix. Compared to the mechan-
SCC with FA and colloidal nS, resulting in a stiffer and stronger
ical mixing of powdered nS with FA or slag, nS premixed with
bond between the aggregates and the matrix. In an another study,
water, i.e., ultrasonicated nS reduced the dormant period of FA
the SEM analysis revealed a strong ITZ in dolomite concrete con-
and slag paste. This effect might be ascribed to the agglomeration
taining 2% nS [68]. The SEM study showed that adding nS and
of fine particles of nS, and subsequent reduction of nucleation sites
mS decreased the transition zone in the expanded polystyrene
needed for the formation of hydration products [34]. They also
structural (EPS) concrete [106].
noticed that the cumulative heat produced during the first 24 h
Esmaeili et al. [58] reported that the nS concrete had uniformly
in both slag and fly ash cement pastes prepared with ultrasoni-
filled microstructure, and the large CH structures were disappeared
cated nS particles was higher than that of nanoparticles mixed
as they were converted into stable and small CSH structures. The
mechanically with other constituents, indicating that the sonica-
size of the CSH structures was extremely fine in nS concrete [96].
tion of nS and water increased the hydration process. Najigivi
According to Quercia et al. [49], such small size CSH structures man-
et al. [97] obtained a uniform dispersion of nS particles by stirring
ifested a higher stiffness values with lower Ca/Si ratio. Similarly, Du
it with water at a high speed of 120 rpm for 1 min. Elkady et al. [46]
et al. [52,77] observed that due to the high pozzolanic reaction of
reported that 5 min sonication of 1% nS particles before adding into
particles of nS, the CH-turned-CSH densified the microstructure
the concrete mix improved the compressive strength by 23% com-
and became more homogeneous. The additional CSH, formed by
pared to the control sample, so the sonication showed a significant
the pozzolanic reaction between nS, replaced the portlandite sheets
effect on de-agglomeration and better dispersion of nS particles
and brought a more refined microstructure in LWC [48]. The pore
when compared to the other de-agglomeration methods such as
size and the interconnections between the pores were found signif-
homogenization and stirring.
icantly reduced due to the refined microstructure [49].
As far as the type (powder or colloidal) of nS is concerned, col-
Backscattered electron (BSE) analysis showed a highly dense
loidal silica has shown a better effect on concrete compared to its
microstructure of HVFA cement paste with 2% nS with few voids
powdered form. Pacheco-Torgal et al. [3] found that the colloidal
and cracks [54]. The nS particles enabled a compact hydration pro-
dispersion of nS was much more effective than the dry powder
duct formation, indicating the fast formation of CSH gel, with a
to control CSH degradation caused by the leaching of calcium.
reduced CH crystals content [43,96]. Ji [105] also noticed that the
Quercia et al. [49] reported that the colloidal nS particles formed
size of the CH crystals and its quantity were reduced, and 70% of
a more refined microstructure in SCC due to their high reactivity
the total hydration product was CSH gel.
and pozzolanic action than that by powdered nS.
Wang et al. 2018 [57] revealed that the addition of nS lowered
The incorporation of nS into the polycarboxylate-based super-
the degree of reaction of FA compared to that in reference concrete.
plasticizer in HPC resulted in much more efficient dispersion and
This was hypothesized due to the high reactivity of nS with CH,
homogenization during concrete mixing, thereby making the con-
which left the system short of CH to react with FA causing imped-
crete easy to use [28]. According to Li et al. [93], nS has much
iment in the hydration of FA. SEM results showed the excessive
higher demand for superplasticizers and cementing efficiency
addition (4%) of nS caused agglomeration of its finer particles
compared to mS.
and formation of the microcracks around them owing to volumet-
ric changes during drying and thus forming weak zones in concrete
[48]. Agglomeration of the nS particle due to its high surface area
9. Combined effect of nS and mS
was also spotted by Alhawat et al. [55].
Esmaeili et al. [58] reported that using 3% nS with 15% mS
8. Effect of size and type of nano silica and its mixing increased the compressive strength by 67.5% compared to the con-
trol mix while adding 9% nS alone showed the strength increase of
Hendrix et al. [107] reported that the optimum concentration of 57.21%. It can be ascribed to the more effective filling effect of the
nS to achieve the best quality of dispersion in the cementitious combined nS and mS particles, which considerably decreased the
16
A. P. P., Dheeresh Kumar Nayak, B. Sangoju et al. Construction and Building Materials 278 (2021) 122347

pores within the cement paste. Similarly, Jalal et al. [43] also 9. Although the nS showed strong advantageous effects on the
observed an enhancement in compressive strength in the binary durability parameters and mechanical properties of different
(cement plus nS or cement plus SF) and ternary system (nS plus sil- types of concrete in different conditions and environments,
ica fume plus cement) of concrete, but the highest was observed in there are still different opinions on the size and type of nS,
the ternary system. its dosage, and dispersion methods, etc. Extensive research
According to Li et al. [93] nS has a much higher demand for in this area, therefore, needs to be carried out in order to
superplasticizers (SP) and cementing efficiency than mS, and the set basic standards for the practical application of such
SP demand for combined nS and mS was not higher than pure nanoparticles.
cement demand. Combined use of nS and mS in concrete increased 10. Consistent improvement in compressive strength and con-
the compressive strength and the elastic modulus, which were crete quality is reported for RAC with nS even at 100% RA
higher than those by using nS or mS alone. The highest values of level. However, extensive study is required to understand
compressive strength and elastic modulus were observed in the the mechanism of improvement in the properties of RAC.
blend of 1% nS and 5% mS at 0.3 w/c ratio. Nili et al. [109] reported
the highest compressive strength in concrete when 1.5% nS added
with 6% mS. Massana et al. [74] also reported that the combined
use of nS and mS demonstrated the highest increase of compres- Declaration of Competing Interest
sive strength in the HPSCC as mentioned earlier under the sub-
heading ‘‘compressive strength” in this article. According to [74], The authors declare that they have no known competing finan-
the inclusion of nS and mS in HPSCC contributed to reducing the cial interests or personal relationships that could have appeared
pores and their critical diameter due to the combined effect of to influence the work reported in this paper.
nS, which reduced the pore size, and mS, which reduced the num-
ber of pores in the concrete. References
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