Article

Experimental Study on the Suitability of Waste Plastics

and Glass as Partial Replacement of Fine Aggregate in
Concrete Production
Alemu Mosisa Legese 1,2, * , Degefe Mitiku 3 , Fekadu Fufa Feyessa 2 , Girum Urgessa 4 and Yada Tesfaye Boru 1,2

1 Faculty of Civil Engineering, Wroclaw University of Science and Technology, Wybrzeże Wyspiańskiego 27,
50-370 Wroclaw, Poland; yada.boru@pwr.edu.pl
2 Faculty of Civil and Environmental Engineering, Jimma Institute of Technology, Jimma University,
Jimma P.O. Box 378, Oromia, Ethiopia
3 Department of Construction Technology and Management, College of Engineering and Technology,
Wollega University, 3HJM+93J, Nekemte P.O. Box 395, Oromia, Ethiopia
4 Sid and Reva Dewberry Department of Civil, Environmental, and Infrastructure Engineering,
George Mason University, Fairfax, VA 22030, USA; gurgessa@gmu.edu
* Correspondence: alemu.legese@pwr.edu.pl

Abstract: Solid waste management is a major environmental challenge, especially in developing

countries, with increasing amounts of waste glass (WG) and waste plastic (WP) not being recycled.
In Ethiopia, managing WG and WP requires innovative recycling techniques. This study examines
concrete properties with WG and WP as partial replacements for fine aggregate. Tests were conducted
on cement setting time, workability, compressive strength, splitting tensile strength, and flexural
strength. Concrete of grade C-25, with a target compressive strength of 25 MPa, was prepared by
partially replacing fine aggregate with WP and WG. The mechanical properties were evaluated after
7 and 28 days of curing. At a 20% replacement level, workability decreased at water–cement ratios of
0.5 and 0.6 but remained stable at 0.4, leading to the selection of the 0.4 ratio for further testing. A
10% replacement of fine aggregate, using a ratio of 3% WP and 7% WG, was found to be optimal,
resulting in an increase in compressive strength by 12.55% and 6.44% at 7 and 28 days, respectively. In
contrast, a 20% replacement led to a decrease in compressive strength by 14.35% and 0.73% at 7 and
28 days, respectively. On the 28th day, the splitting tensile strength at the optimal replacement level
Citation: Legese, A.M.; Mitiku, D.; was 4.3 MPa, reflecting an 8.5% reduction compared to the control mix. However, flexural strength
Feyessa, F.F.; Urgessa, G.; Boru, Y.T. improved significantly by 19.7%, from 12.46 MPa to 15.52 MPa. Overall, the incorporation of WG and
Experimental Study on the Suitability WP in concrete enhances flexural strength but slightly reduces splitting tensile strength.
of Waste Plastics and Glass as Partial
Replacement of Fine Aggregate in
Keywords: fine aggregate replacement; recycling; waste glass; waste plastics
Concrete Production. Constr. Mater.
2024, 4, 581–596. https://doi.org/
10.3390/constrmater4030031

Received: 26 June 2024 1. Introduction

Revised: 13 August 2024
The amount of waste generated by various industrial sectors is steadily increasing,
Accepted: 15 August 2024
posing a major environmental problem. It is a common objective of sustainable global
Published: 4 September 2024
development goals to fight the climate crisis by recycling waste materials to reduce the vol-
ume of solid waste at disposal sites [1–7]. Currently, about 8.3 billion metric tons of plastic
are generated globally and this is expected to increase to 12 billion by 2050. However, only
Copyright: © 2024 by the authors.
9% of these are recycled, and 6.3 billion are accumulated in landfills or sloughing off in the
Licensee MDPI, Basel, Switzerland. natural environment. Moreover, as of 2018, the glass industry reported recycling around
This article is an open access article 27 million metric tons globally, accounting for about 21% of total glass production [8].
distributed under the terms and Therefore, solid waste reuse in the construction industry is gaining attention in developed
conditions of the Creative Commons countries. Currently, the scarcity of construction materials and excessive disposal of waste
Attribution (CC BY) license (https:// products are the difficulties experienced globally that need a rapid and permanent solu-
creativecommons.org/licenses/by/ tion [9,10]. Notably, this process has led scholars to tackle the issue of finding suitable
4.0/). eco-friendly construction materials and handle environmental matters simultaneously [11].

Constr. Mater. 2024, 4, 581–596. https://doi.org/10.3390/constrmater4030031 https://www.mdpi.com/journal/constrmater

Constr. Mater. 2024, 4 582

Recently, there has been some evidence of waste materials and by-products used in con-
struction materials. However, recycling waste as an alternative construction material is
used significantly less in developing countries [12]. The usage of these materials aids in
their integration into cement, concrete, and other construction materials but also assists in
lowering the cost of cement production by reducing energy consumption and improving
environmental protection from potential carbon emissions [13–16].
Recycling waste glass and plastic has always been an issue globally, even though the
recycling rate of glass is relatively high compared with plastics [17]. A lot of research has
been conducted on recycling plastic waste in mortar [18–22] and concrete [23–26]. Other
studies have been conducted on the recycling of waste glass in concrete as a fine aggregate
replacement [1,17,27], coarse aggregates as an additive [27–31], partial replacement of
cement [32–35], and as fine aggregates [36] in mortar. In other studies, fine aggregates used
in concrete mixtures are substituted in proportions by shredded plastics and glass, and the
optimal amount is determined at which greater strength is attained [37–39]. Concrete from
plastic and glass wastes has several benefits including being lightweight, robust, simple to
shape, and customized to various customer needs [40].
The use of glass wastes as fine aggregates improves the physical and mechanical
properties of concrete by reducing the density, and they are effective in controlling the
structure’s weight for stability purposes [41]. On the other hand, crushed glass contains
engineering characteristics of an angular and somewhat elongated shape. This situation
creates a higher internal friction angle, improving the interlocking between different in-
gredients of concrete particles. Partial replacement of waste glass does not significantly
affect the workability of the concrete [42]. However, it has been shown that the compressive
strength decreases by almost 49% with a 60% of WG [42].
On the other hand, the addition of waste glass as fine aggregates increases the me-
chanical properties of mortar [36]. Replacing the natural sand with recycled high-density
polyethylene (HDPE) aggregates increased the axial deformation capability of mortar and
reduced the density [21]. Waste plastic as coarse aggregates in the concrete also increases
the workability of concrete [43]. The rise in slump indicates that more water was available
from the mix due to decreased absorption by reducing the percentage volume of natural
aggregates and low water absorption by recycled plastics [44,45]. Many authors reported
a gradual decrease in the compressive strength by increasing the percentage of waste
plastic [46–48]. Their findings show that the addition or partial replacement of WG and WP
has positive and negative effects on the concrete’s fresh and hardened properties. However,
limited research is available on the combination of WG and WP in concrete as a partial
replacement for fine aggregates. The primary aim of this research is to investigate the
properties and performance of concrete produced using waste glass (WG) and waste plastic
(WP) as partial replacements for fine aggregate. This study seeks to evaluate the potential
benefits and challenges of incorporating these waste materials into concrete mixtures, in-
cluding their impact on the mechanical properties. By exploring these factors, the research
aims to contribute to more sustainable construction practices and the effective utilization of
waste materials.

2. Materials and Methods

Comprehensive experimental tests were conducted to study the characteristics and
strength properties of the partial replacement of fine aggregates with plastic and glass
waste on concrete’s fresh and hardened properties. Potential waste glass quantities were
collected from empty glass containers and various building and construction remnant
materials commonly used for laboratory procedures. The waste glass was crushed into fine
pieces that resembled the size of sand. On the other hand, samples of granulated plastic
waste, mostly soda and water bottles, were collected from a dumpsite. Waste plastics
should be cleaned before use to remove debris and impurities that could alter the hydration
and bonding of the cement paste. The plastic samples were selected to fit the sieve’s size
requirements at the laboratory.
Constr. Mater. 2024, 4 583

The proportion by weight of all constituents (aggregates, cement, plastics, glass, and
water) was kept constant in all the mixes. The ACI mix design method arrived at the right
combination of cement, fine aggregate, coarse aggregate, and water for C-25 grade concrete.
Finally, different experiments were conducted on concrete properties with various mixing
and curing parameters. For this study, the ratios of the weight of waste plastics to glass
used were 3:7, 6:14, and 10:20. The optimum mix ratio was determined.

2.1. Cement
Ordinary Portland cement (OPC) with a grade of 42.5 N manufactured by the Derba
Midroc Cement PLC in Salale Zone, Oromia Regional State, Ethiopia was selected for
this study. The physical and mechanical properties were studied using the requirements
specified by ASTM and are presented in Table 1. Cement pastes with different water–
cement ratios generally have other setting times. Therefore, it does not seem apparent at
first which setting time to use. The setting time of a cement paste with a typical consistency
is referred to as the setting time of cement paste by convention [49]. The initial setting time
is the duration of cement paste related to 25 mm penetration of the Vicat needle into the
paste 30 s after it is released.

Table 1. Physical properties of Derba cement.

Physical Properties Test Results Recommended Value

Consistency (%) 31 26–33 [49]
Initial Setting Time (min) 52 more than 45 min [50]
Final Setting Time (min) 320 not more than 375 [50]

In contrast, the final setting time is related to zero penetration of the Vicat needle into
the paste [49]. The standard consistency for hydraulic cement refers to the amount of water
required to make a neat paste of satisfactory workability. The Vicat apparatus was used to
assess the paste’s resistance to penetration by applying a 300-gram plunger to its surface.
The mechanical property of the cement used in this study is shown in Table 2.

Table 2. Mechanical property of Derba cement.

Mechanical Property Test Results

3rd day compressive strength (MPa) 23.20
7th day compressive strength (MPa) 33.40
28th day compressive strength (MPa) 45.70

2.2. Aggregate
The fine aggregate (river sand) used for this research work was brought from suppliers
of Jimma town, Ethiopia, and was originally from Gambela, Ethiopia, and crushed coarse
aggregate was bought from the crusher site located in Jimma town. Aggregate grain size
distribution or gradation is one of the properties of aggregates that influences the quality
of concrete. Therefore, fine aggregates and coarse aggregates with gradation satisfying
the grading requirement of the ASTM standard [51], shown in Figures 1 and 2, were used
throughout the experiment.
Therefore, the grain size distribution curve exhibits a fine aggregate sample employed
for this research task as a well-graded type of aggregate. The percentage passing of fine
aggregate runs in the lower and upper limit of the standard requirement gradation curve.
 %Passing
100 Lower limit
Upper limit
Constr. Mater.
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80

Passing (%)
60
%Passing
100 Lower limit
40 Upper limit

80
20

Passing (%)
60
0
40
0.1 1 10
20 Particle Diameter size (mm)

Figure 1. Grain size distribution curve of fine aggregate.

0
Therefore, the grain size distribution curve exhibits a fine aggregate sample em-
0.1 1 10
ployed for this research task as a well-graded type of aggregate. The percentage passing
Particle Diameter size (mm)
of fine aggregate runs in the lower and upper limit of the standard requirement gradation
curve.
Figure1.1.Grain
Figure Grainsize
size distribution
distribution curve
curve of aggregate.
of fine fine aggregate.

Therefore, the grain sizeDistribution

Grain Szie distributionCurve -curve
Coarseexhibits
aggregate a fine aggregate sample em
ployed for this research task as a well-graded type of aggregate. The percentage passing
%Passing
of 100
fine aggregate runs in the lower and upper limit of the standard requirement gradation
Lower limit
Upper limit
curve.
80
Grain Szie Distribution Curve - Coarse aggregate
Passing (%)

60
%Passing
100 Lower limit
40 Upper limit

80
20
Passing (%)

60
0
40
10
20 Particle Diameter szie (mm)

Figure2.2.Grain
Figure Grainsize distribution
size curve
distribution of coarse
curve aggregate.
of coarse aggregate.
0
2.3. Waste Plastics
2.3. Waste Plastics
Forty-three (43) kg samples of the 10 waste plastic particles, mostly soda and water
Forty-three
bottles, (43) kg
were collected samples
from plastic ofdisposed
the
Particle
waste
Diameterin
plastic
sziethe
(mm)
particles,
Jimma mostly
town bore soda and
dumping site water
in bot-
tles, werehigh-density
Ethiopia. collected from plastic disposed
polyethylene (HDPE) in and the Jimma town
Polyethylene bore dumping
Terephthalate (PET) site
arein Ethio-
Figure
two
pia. 2. Grain
types
high-densitysize polyethylene
of commonlydistribution curve
used plastics of coarse
made
(HDPE) for
and aggregate.
everyday use. For this
Polyethylene study, PET types
Terephthalate (PET)of are two
plastics
types ofwere selectedused
commonly sinceplastics
they canmadebe found in high volumes
for everyday use. Forinthis
dumpsites relative
study, PET to of plas-
types
2.3. Waste
others. The Plastics
collected plastics were cleaned
tics were selected since they can be found in from impurities with tap water and then air-
high volumes in dumpsites relative to others
dried.Forty-three
The air-dried sample was melted at 130 ◦ C, cooled to make it suitable for crushing,
(43) kg
The collected plastics samples
were cleaned of from
the waste plasticwith
impurities particles, mostly
tap water andsoda
thenand water The
air-dried. bot
and converted to a fine-sized aggregate. The production process of the fine waste plastic is
tles, weresample
air-dried collected from
was plastic
melted at disposed
130 °C, in thetoJimma
cooled make town
it bore dumping
suitable for site and
crushing, in Ethio
con-
illustrated in Figure 3. Finally, a sieve analysis was conducted and the required size of the
pia. high-density
verted
plastic to a fine-sized
aggregate
polyethylene
aggregate.as(HDPE)
was determined, The and
production
illustrated
Polyethylene
in Figureprocess
3.
Terephthalate
of the (PET) are
fine waste plastic two
is illus-
types of
trated incommonly used plastics
Figure 3. Finally, made
a sieve for everyday
analysis use. For and
was conducted this study, PET types
the required sizeofofplas
the
tics were
plastic selectedwas
aggregate sincedetermined,
they can beasfound in highinvolumes
illustrated in dumpsites relative to others
Figure 3.
The collected plastics were cleaned from impurities with tap water and then air-dried. The
air-dried sample was melted at 130 °C, cooled to make it suitable for crushing, and con
verted to a fine-sized aggregate. The production process of the fine waste plastic is illus
trated in Figure 3. Finally, a sieve analysis was conducted and the required size of the
plastic aggregate was determined, as illustrated in Figure 3.
Constr. Mater.
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2024, FOR PEER
FOR REVIEW
PEER REVIEW 55
Constr. Mater. 2024, 4 585

Figure
Figure3.3.Fine waste
Fine plastic
waste preparation
plastic process:
preparation process:(a)(a)
collection, (b)(b)
collection, cleaning, (c)(c)
cleaning, crushing, (d)
crushing, melted
(d) melted
and grinded.
and grinded.

The
Thephysical
physicalproperties
propertiesofofthe
theplastic
the plasticand
plastic andglass
and glasswaste
glass wasteare
waste aresummarized
are summarizedinin
summarized inTable
Table3.3.
Table 3.

Table
Table
Table3.3.
Physical
3. Physicalproperties
properties
propertiesofof
plastic
of and
plastic
plastic glass
and
and waste.
glass
glass waste.
waste.

Properties
Properties
Properties Test
Test
Test Results
Results
Results ASTM
ASTMCode
Code
ASTM Standards
Standards
Code [52]
[52]
Standards [52]
-- Plastic
Plasticwaste
waste Glass waste
Glass waste Recommended
Recommended
- Plastic Waste Glass Waste Recommended
Fineness
Fineness modulus(FM)
modulus (FM) 2.52
2.52 2.56
2.56 --
Fineness modulus (FM) 2.52 2.56 -
The nominal maximum size,
The nominal maximum size, (mm) (mm)
The nominal maximum size,(mm) 0.075–4.00
0.075–4.00
0.075–4.00
0.075–4.00
0.075–4.00
0.075–4.00
-- -
Specific
Specific
Specific gravity
gravity
gravity (SSD basis)
(SSD basis)
(SSD basis) 1.09 1.09
1.09 2.62
2.62
2.62 2.3‒2.9
2.3‒2.9
2.3–2.9
Unit
Unit weight,
weight, (kg/m 3)
(kg/m 3) 3 65 6565 2450 2450 1280–1920
1280–1920
Unit weight, (kg/m ) 2450 1280–1920
Water
Waterabsorption
Waterabsorptioncapacity, (%)
absorptioncapacity,
capacity,(%) (%) 0.00 0.00
0.00 0.01 0.01
0.01 0.4–4.0
0.4–4.0
0.4–4.0

The
Thegrain
grainsize
sizedistribution
distributioncurve
curveofoffine
finewaste
fine wasteplastics
plasticsisisillustrated
illustratedininFigure
Figure4.4.
Figure 4.

Grain Size
Grain Distribution
Size Curve-
Distribution Waste
Curve- Plastic
Waste finefine
Plastic aggregate
aggregate

100 %Passing
%Passing
100 Lower limitlimit
Lower
Upper limitlimit
Upper

8080
Passing (%)
Passing (%)

6060

4040

0.10.1 11 1010
Particle Diamter
Particle Size
Diamter (mm)
Size (mm)

Figure 4.4.
Figure
Figure Grain
4. size
Grain
Grain distribution
size
size curve
distribution
distribution ofof
curve
curve fine-
of fine-waste
fine- plastics.
waste
waste plastics.
plastics.

2.4.
2.4. Waste
2.4.Waste
Waste Glass
Glass
Glass
Seventy-two
Seventy-two
Seventy-two(72)(72)
(72)kgkg
kgofof waste
ofwaste glass
wasteglass materials
glassmaterials was
materialswas used
wasused throughoutthis
usedthroughout
throughout this experimental
thisexperimental
experimental
study,
study, gathered
study,gathered from
gatheredfrom
fromthethe disposals
disposalsofof
thedisposals reconstruction
ofreconstruction and
reconstructionand building
andbuilding demolition
buildingdemolition projects
projectsinin
demolitionprojects in
the Jimma town bore solid-waste dumping site. Soda-lime-type glass was used for the
Constr. Mater. 2024, 5, FOR PEER REVIEW 6
Constr. Mater. 2024, 5, FOR PEER REVIEW 6
Constr. Mater. 2024, 4 586

the Jimma town bore solid-waste dumping site. Soda-lime-type glass was used for the
the Jimma town bore solid-waste dumping site. Soda-lime-type glass was used for the
investigation throughout this research study among different glasses. For this task, the
investigation
investigation throughout this research study among different glasses. For this
For task, the
collection of wastethroughout this
and glass focused research study
on a ‘bore’ among
dumping different glasses.
site in Jimma town. this
The task,
col- the
collection
collection of waste
of waste and
and glass focused
glass focused on a ‘bore’ dumping
on a ‘bore’ dumping site in
site in Jimma
Jimma town.
town. The
The col-
collected
lected waste
lected glass
waste waswas
glass contaminated
contaminated with
withimpurities
impurities that
thatcould
could have
have altered
altered the
the glass’s
glass’s
waste
chemical glass
andand was
physicalcontaminated
properties. with impurities
Therefore, the that could have altered the glass’s chemical
chemical
and physical physical properties.
properties. Therefore,
Therefore, the wastethewaste
glass
glass
wastewasglasswas
wascleaned
cleaned cleaned with pure water
withwater
with pure pure water
to remove
to remove
to impurities.
remove impurities. Then, the cleaned waste glass was ground into a fine aggregate size
impurities. Then, theThen, the waste
cleaned cleanedglass
wastewasglass was ground
ground into aggregate
into a fine a fine aggregate size
size manually
manually
manuallyusing a hammer.
using a hammer.
using a hammer.
Finally, the the
Finally, crushed waste glass was sieved,
sieved,and
andthe
therequired
required sizesize was
was obtained, as
Finally, thecrushed
crushedwaste
waste glass
glasswas
was sieved, and the required size obtained, as
was obtained, as
shown in Figure
shown 5. 5.
in Figure
shown in Figure 5.

Figure 5.5.Granulated
Granulated glass particles used forfor
testing: (a) collected sample, (b) cleaned, crushed, and and
Figure
Figure 5. Granulated
sieved waste glass.
glassglass particles
particles usedused testing:
for testing: (a) collected
(a) collected sample,
sample, (b) cleaned,
(b) cleaned, crushed,
crushed, and
sieved
sieved wastewaste
glass.glass.
The grain size distribution curve of of
thethe
fine waste glass is illustrated in Figure 6. 6.
The The
graingrain
size size distribution
distribution curve
curve of the fine fine
wastewaste
glassglass is illustrated
is illustrated in Figure
in Figure 6.
Grain Size Distribution Curve- Waste glass Fine aggregate
Grain Size Distribution Curve- Waste glass Fine aggregate
%Passing
100 Lower limit
%Passing
Upper limit
100 Lower limit
80 Upper limit

80
Passing (%)

60
Passing (%)

60
40
40
20

20
0

0 0.1 1 10
Particle Diameter szie (mm)
0.1 1 10
Figure 6. Grain size distribution
Particle curve ofszie
Diameter fine(mm)
waste glass.
Figure 6. Grain size distribution curve of fine waste glass.
2.5. Mix Designing and Proportioning
Figure
2.5.6.Mix
Grain size distribution
Designing curve of fine waste glass.
and Proportioning
The material properties (cement, aggregate, shredded plastics, and waste glass) and
The material
concrete properties
characteristics (cement,the
containing aggregate, shredded
waste glass plastics,
and plastic wereand waste glass)
examined. and
In addition,
2.5. Mix Designing and Proportioning
concrete characteristics containing the waste glass and plastic were examined.
the mathematical approach to the volume-based analysis of materials was considered for In addition,
The material properties
the approach(cement, aggregate, shredded plastics, and waste glass) and
themathematical
concrete mix production totothe volume-based
evaluate analysis
the physical andof materials
mechanical was considered
properties for
(workability,
concrete
the characteristics
concrete mix containing
production to the waste
evaluate glass
the and plastic
physical and were examined.
mechanical In addition,
properties (worka-
compressive strength, flexural strength, and splitting tensile strength).
the mathematical
bility,The approach
compressive to the
strength, volume-based
flexural analysis
strength,sand,
and spli of materials
ing tensile was considered for
strength).
appropriate quantities of cement, aggregates, waste plastics, and glass were
the concrete
The mix production to evaluate the physical and mechanical
waste properties (worka-
used to create a concrete mix. The main purpose here was to find theplastics,
appropriate quantities of cement, sand, aggregates,
optimum and glass
replacement
bility, compressive strength, flexural strength, and spli ing tensile strength).
were used to create a concrete mix. The main purpose here was to find the optimum re-
of waste plastics and glass that could be utilized to manufacture concrete that meets the
placement of waste quantities
The appropriate plastics andofglass that could be
cement, utilized to manufacture concrete that
performance standards of concrete undersand,
loadsaggregates,
and in diverse waste plastics,
environments. and glass
weremeets
usedthe
to performance standards
create a concrete mix. ofThe concrete under loads
main purpose hereand
wasinto
diverse environments.
find the optimum re-
placement of waste
2.5.1. Mix Design plastics and Plastics
for Waste glass that to could
Glass be utilized to manufacture concrete that
meets theDifferent
performance standards of concrete
trial mixes were proportioned underby loads and in diverse
observing environments.
concrete’s workability and
compressive strength to obtain the appropriate waste plastic and glass ratio. As a result, the
optimum ratio of WP to WG was determined. Table 4 summarizes the mix properties of the
Constr. Mater. 2024, 4 587

concrete mix without any waste glass and plastics content for three various water–cement
ratios. These ratios cover the most widely applicable engineering practices, from 0.4 to 0.6.
The mixes conform to the standards and specifications of ASTM C136 [51] and ASTM C
33-03 [52]. Finally, the mix proportion for the C-25 concrete grade is tabulated in Table 5
with different water–cement ratios.

Table 4. Mix proportioning for one m3 of concrete.

Cement Water Fine Agg Coarse Agg Plastic Waste Glass Waste
Type of Mix w/c
(kg/m3 ) (kg/m3 ) (kg/m3 ) (kg/m3 ) (kg/m3 ) (kg/m3 )
Control 0.4 475 165 768 1007 0.0 0.0
Control 0.5 380 162 850 1007 0.0 0.0
Control 0.6 316.67 160 905 1007 0.0 0.0

Table 5. Design of concrete mixtures and number of test specimens for compressive strength at each
test age.

Number of Compressive Strength Tests

Group No w/c Ratio % of WP and WG WP: WG Ratio
7th Day 28th Day
WPG-0 0 0:0 3 3
WPG-1 10 3:7 3 3
0.4
WPG-2 20 6:14 3 3
WPG-3 30 10:20 3 3
WPG-0 0 0:0 3 3
WPG-1 10 3:7 3 3
0.5
WPG-2 20 6:14 3 3
WPG-3 30 10:20 3 3
WPG-0 0 0:0 3 3
WPG-1 10 3:7 3 3
0.6
WPG-2 20 6:14 3 3
WPG-3 30 10:20 3 3

With different controlling factors, such as water–cement ratio, waste plastics, and glass
proportions, four mixes and 72 standard compressive sample specimens were used in the
experiments. For comparison purposes, the reference testing samples were plain concrete
with no WG and WP content. Table 5 summarizes the complete experimental plan.

2.5.2. Mix Design for Fine Aggregate, Waste Plastic, and Glass
The testing program continued focusing only on the two mixes with optimal output
results, i.e., sample WPG-0 at a water–cement ratio of 0.4 and 20% of the fine aggregate
replaced by WG and WP. We used a w/c ratio of 0.40 because the concrete workability
was stable compared to the control mixture. However, the workability and strength of
the concrete are affected when using a w/c ratio above 0.50. Based on these results, an
extra series of 12 tests were conducted to determine the flexural strength and the splitting
resistance of the two optimal concrete mixes. The trial mix for WP and WG using a
water–cement ratio of 0.4 is described in Table 6.
Constr. Mater. 2024, 4 588

Table 6. Trial mix for waste plastic and glass ratio for water–cement ratio of 0.4.

Mix Ratio of Cement Water Fine Agg Coarse Agg Plastic Waste Glass Waste
Type of Mix
WP to WG (kg/m3 ) (kg/m3 ) (kg/m3 ) (kg/m3 ) (kg/m3 ) (kg/m3 )
Control (WPG-0) N/A 38.475 13.65 62.20 81.57 0.00 0.0
WPG-1 1:1 38.475 13.65 49.76 81.57 6.22 6.22
WPG-2 1:1.5 38.475 13.65 49.7664 81.57 4.976 7.46
WPG-3 1:2 38.475 13.65 49.76 81.57 4.15 8.29
WPG-4 1:2.5 38.475 13.65 49.76 81.57 3.55 8.88
WPG-5 1:3 38.475 13.65 49.76 81.57 3.11 9.33

The mix proportions for compressive strength at the 7th and 28th days with different
water–cement ratio are summarized in Table 7.

Table 7. Mix proportions for 0.081 m3 of concrete.

Cement Water Fine Agg Coarse Agg Plastic Agg Glass Agg
Type of Mix w/c
(kg/m3 ) (kg/m3 ) (kg/m3 ) (kg/m3 ) (kg/m3 ) (kg/m3 )
Plain (PG-0) 0.4 38.475 13.65 62.20 81.57 0.00 0.0
WPG-1 0.4 38.475 13.65 55.9872 81.57 2.0736 4.1472
WPG-2 0.4 38.475 13.65 49.7664 81.57 4.1472 8.2944
WPG-3 0.4 38.475 13.65 43.5456 81.57 6.2208 12.4416
Plain (PG-0) 0.5 30.78 13.12 68.85 81.57 0.0 0.0
WPG-1 0.5 30.78 13.12 61.965 81.57 2.295 4.59
WPG-2 0.5 30.78 13.12 55.08 81.57 4.59 9.18
WPG-3 0.5 30.78 13.12 48.195 81.57 6.885 13.77
Plain (XPG-0) 0.6 32.7 25.65 73.305 81.57 0.0 0.0
WPG-1 0.6 32.7 25.65 65.9745 81.57 2.4435 4.887
WPG-2 0.6 32.7 25.65 58.644 81.57 4.887 9.774
WPG-3 0.6 32.7 25.65 51.3135 81.57 7.3305 14.661

2.6. Concrete Specimens Preparation

Initially, a certain amount of water was added to the aggregates and left for a short
while to bring the aggregates to the saturated surface dry condition (SSD). Next, the fine
aggregate, coarse aggregate, and cement were dry mixed for about a minute. Next, the fine
glass and plastic wastes were carefully added to the dry mix to avoid segregation, followed
by the addition of two-thirds of the total mixing water.
Twelve 150 mm cubes, three 150 × 300 mm cylinders, and three 100 × 100 × 500 mm
beams were cast for each mix. Cubes were used to measure the compressive strength on the
Constr. Mater. 2024, 5, FOR PEER REVIEW 9
7th and 28th days. In addition, the 28th day’s tensile strength and flexural tensile strength
were evaluated using cylinder specimens and beam specimens, as shown in Figure 7.

Figure7.7.Sample
Figure Sampleunder
under test:
test: (a) flexural
flexural strength,
strength,(b)
(b)tensile
tensilestrength, (c)(c)
strength, failure under
failure tensile
under test.test.
tensile

3. Results and Discussions

3.1. The Test Program for Concrete Mix Design
For the laboratory procedures, the concrete grade C-25 compressive strength was
used to understand the effect of compressive strength.
Constr. Mater. 2024, 4 589

3. Results and Discussions

3.1. The Test Program for Concrete Mix Design
For the laboratory procedures, the concrete grade C-25 compressive strength was used
to understand the effect of compressive strength.
The ratios of plastics to glass in the mix were determined by using the estimated
quantity of waste with a water-to-cement ratio of 0.4 and observing the effect on the
compressive strength of the concrete on the 7th day (Table 8).

Table 8. Compressive strength of concrete at 7 days for varying ratios of waste plastics to waste glass
(WP:WG).

7th-Day Compressive
Group Number WP:WG -
Strength (MPa)
Mean 20.6
(Control) 0:0
Standard deviation 0.20
Mean 16.2
M2-PG-2 1:1.5
Standard deviation 0.30
Mean 19.27
M2-PG-2 1:1.5
Standard deviation 0.152
Mean 20.46
M4-PG-4 1:2.5
Standard deviation 0.155
Mean 20.8
M5-PG-5 1:3
Standard deviation 0.10

As shown in Table 8, the compressive strength increases as the ratio of plastics in the
mix decreases and the glass increases. It shows that the added glass has positive effect by
improving the compressive strength of the concrete, compared with the waste plastic.
The mean concrete compressive strength on the 7th day for the ratio of WP to WG
(1:1, 1:1.5, 1:2, 1:2.5 and 1:3) was compared with the control mix concrete’s compressive
strength. From the proportions of the plastics to glass, a ratio of 1:2 was selected because in
the first two ratios the compressive strength decreased, while in the 1:2.5 ratio and 1:3 ratio,
the amount of glass was high and amount of plastic was low, but the strength met the
standard. However, these ratios were not selected since the quantity of glass in the mix
was significantly higher than the combined plastic quantity.
When the ratios of plastic to glass were 1:2, 1:2.5, and 1:3, the mean compressive
strength of the concrete was almost equal with the control mix, as shown in Table 8. Thus,
for practical purposes in terms of the proportions of the plastics to glass, a ratio of 1:2I was
selected due to the fact that the volume of the plastic waste is much greater than that of
glass wastes in the study area of this research. However, from a scientific point of view, a
ratio of 1:3 is recommended since the maximum compressive strength was observed at this
mix ratio.
Thus, it is inferred that the replacement of sand with plastic waste up to 15% can
be adopted so that the disposal of used plastic can be reduced and the lack of natural
aggregates can be managed effectively [53].
When 30% of the fine aggregate was replaced by waste glass, the strength was only
about 1% lower than that of the control, which is a promising result [35]. Therefore, the
1:2 ratio was selected as the optimum ratio of plastics to glass in the mix during the
investigation.

3.2. Effect of Waste Plastics and Glass on the Workability of Concrete

As shown in Table 9, the fresh concrete workability was inversely affected by the
increase in water–cement ratio and decreased as the percentage of fine WP and WG
was increased.
 tigation.

3.2. Effect of Waste Plastics and Glass on the Workability of Concrete

As shown in Table 9, the fresh concrete workability was inversely affected by th
Constr. Mater. 2024, 4 increase in water–cement ratio and decreased as the percentage of fine WP and
590 WG wa
increased.

Table 9. Slump Table 9. Slump test results.

test results.
Slump
Slump Test Slump Slump Test Slump
Grade w/c Grade
Samplew/c Sample w/c Slump
Grade w/cGradeSample
Test
Sample Test
Grade Grade Sample
w/c w/c Sample
(mm) Test (mm) (mm) (mm) Test (mm
(mm)
0.4 PG-0 0.4 10PG-0 10 0.5 PG-00.5 95
PG-0 95 0.6 PG-0
0.6 240
PG-0 240
0.4 PG-1 9.5 C- 0.5 PG-1 90 C- 0.6 PG-1 230
C-25 0.4 PG-1 9.5 0.5 PG-1 90 0.6 PG-1 230
0.4 PG-2
C-25 7 25 0.5 C-25 PG-2 80 25 0.6
C-25 PG-2 220
0.4 PG-3 0.4 7PG-2 7 0.5 PG-30.5 PG-2
30 80 0.6 0.6
PG-3 PG-2
210 220
0.4 PG-3 7 0.5 PG-3 30 0.6 PG-3 210

Clearly, fine WP and WG

Clearly, fine in
WPconcrete
and WGsignificantly decreased the
in concrete significantly workability.
decreased Specifi- Specif
the workability.
cally, for a w/cically,
ratiofor
of 0.4
a w/c ratio of 0.4 replacing 10% of the fine aggregate with fine WPthe
replacing 10% of the fine aggregate with fine WP and WG, and WG, th
change was negligible. However,
change was negligible. it significantly decreased the
However, it significantly workability
decreased for a w/c ratio
the workability for a w/c rati
of 0.5 and above theand
of 0.5 fineabove
WP and
the WG
fine WPintroduced
and WGto the concrete.
introduced to the concrete.
Generally, theGenerally,
water to cement ratio
the water affectedratio
to cement the affected
concretethe
workability, rather thanrather
concrete workability, the than th
introduction ofintroduction
waste plastics and glass
of waste to the
plastics andmix.
glassThe slump
to the mix. tests with and
The slump testswithout
with andthe
without th
wastes are shown in Figure
wastes 8. in Figure 8.
are shown

Figure 8. Example of slump

Figure test (a)
8. Example of for plain
slump concrete
test and (b)
(a) for plain for waste
concrete plastic
and (b) and glass.
for waste plastic and glass.

3.3. Unit Weight

3.3.Test Results
Unit Weight Test Results
The results forThe
different sample
results groupssample
for different regarding the unit
groups weightthe
regarding forunit
hardened
weightconcrete
for hardened con
are listed in Table
crete10.
are listed in Table 10.
Table 10. Unit weight of concrete with series of proportions of fine waste plastics and glass contents.

Specimen w/c Waste (%) WP:WG Unit wt. (g/cm3 ) Reduction (%)
WPG-0 0.4 0 0 2.35 0.00
WPG-1 0.4 10 3:7 2.39 1.70
WPG-2 0.4 20 6:14 2.33 0.85
WPG-3 0.4 30 10:20 2.37 0.85
WPG-0 0.5 0 0 2.36 0.00
WPG-1 0.5 10 3:7 2.49 5.5
WPG-2 0.5 20 6:14 2.24 5.08
WPG-3 0.5 30 10:20 2.29 2.97
WPG-0 0.6 0 0 2.19 0.00
WPG-1 0.6 10 3:7 2.05 6.40
WPG-2 0.6 20 6:14 2.01 8.22
WPG-3 0.6 30 10:20 2.0 8.67

It was shown that the concrete unit weight decreased as the water–cement ratio
increased. For example, at a water–cement ratio of 0.4, the maximum reduction was 1.7%;
at a water–cement ratio of 0.5, the maximum reduction in unit weight was 5.5%; and at a
water–cement ratio of 0.6, the maximum reduction was 8.67%. According to ASTM C 33,
Constr. Mater. 2024, 4 591

the concrete unit weight at w/c = 0.4 fulfills the requirements of normal weight concrete: it
must be between 2.2 and 2.4 (g/cm3 ). Therefore, a water–cement ratio of 0.4 was selected
for the investigation since the percentage of reduction in unit weight was minimal.

3.4. Effect of Waste Plastics and Glass on Compressive Strength of Concrete

As shown in Table 11, at water–cement ratios of 0.4 and 10% WP and WG, the com-
pressive strength at 7 and 28 days was increased by 12.55% and 6.44%, respectively. Never-
theless, at w/c = 0.5 and 0.6 and all introductions of WP to WG, the compressive strength
at 7 and 28 days was decreased. On the other hand, at 20% replacement, a reduction
was observed by 14.35% and 0.73% on the 7th and 28th day, respectively. In this case,
the concrete designs for C-25, on the 28th day, the compressive strength was 26.9 MPa.
Therefore, if the impact of the WG and WP on the environment was considered a primary
issue, it is possible to use up to 20% replacement for fine aggregate for simple structures
where lightweight concrete is required.

Table 11. The 7- and 28-day compressive strengths of concrete with several fine waste plastic to glass
contents at different water–cement ratios.

Compressive Strength (MPa) Strength Change (%)

Samples w/c WP and WG (%) WP:WG
7 Days 28 Days 7 Days 28 Days
WPG-0 0 0 22.3 27.1 0.00 0.00
WPG-1 10 3:7 25.1 28.9 +12.55 +6.64
0.4
WPG-2 20 6:14 19.1 26.9 −14.35 −0.73
WPG-3 30 10:20 15.0 25.4 −32.74 −6.27
WPG-0 0 0 20.7 27.3 0.00 0.00
WPG-1 10 3:7 19.1 26.8 −7.73 −1.83
0.5
WPG-2 20 6:14 18.3 25.2 −11.59 −7.70
WPG-3 30 10:20 16.8 25.0 −18.84 −8.82
WPG-0 0 0 20.5 27.0 0.00 0.00
WPG-1 10 3:7 15.5 22.5 −24.39 −16.67
Constr. Mater. 2024, 5,0.6
FOR PEER REVIEW 12
WPG-2 20 6:14 16.2 21.5 −20.97 −20.37
WPG-3 30 10:20 14.3 19.2 −30.92 −28.89

A summary of the effect of the water–cement ratio on compressive strength is shown

A summary
in Figure 9. It canof
bethe effect of
observed thethe
that water–cement
compressive ratio on compressive
strength decreases as strength is shown in
the water–ce-
Figure
ment ratio increases across all tested percentages of waste materials used as fine aggregate ratio
9. It can be observed that the compressive strength decreases as the water–cement
increases across all tested percentages of waste materials used as fine aggregate replacements.
replacements.

Figure 9.
Figure 9. Compressive
Compressive strength
strength at
atdifferent
differentpercentages
percentagesofofwaste
waste materials
materials and
and various
various water–ce- ratios.
water–cement
ment ratios.

3.5. Optimal Waste Plastic and Glass Contents in Concrete Mixes

As shown in Table 12, the optimum compressive strength was obtained with a 10%
replacement of fine aggregate by WG and WP. However, as discussed earlier, utilizing a
20% replacement is also feasible, as the mean compressive strength on the 28th day re-
Constr. Mater. 2024, 4 592

3.5. Optimal Waste Plastic and Glass Contents in Concrete Mixes

As shown in Table 12, the optimum compressive strength was obtained with a 10%
replacement of fine aggregate by WG and WP. However, as discussed earlier, utilizing
a 20% replacement is also feasible, as the mean compressive strength on the 28th day
remains sufficient. This approach will help increase the percentage of waste materials
being recycled.

Table 12. The 7- and 28-day compressive strength of concrete at w/c = 0.4.

7-Days Compressive 28-Days Compressive

Group No. WP and WG (%)
Strength (MPa) Strength (MPa)
WPG-0 0 22.3 27.1
WPG-1 10 25.1 28.9
WPG-2 20 19.1 24.9
WPG-3 30 15.0 24.4

3.6. Effect of Waste Plastic and Glass on Flexural Strength

The prepared beam samples were tested after 28 days of standard curing, and the
results of the flexural strength tests for the control concrete and the waste plastics and glass
concretes are illustrated in Figure 9. The bending strength of the concrete (σ) in MPa was
obtained based on Equation (1).
MC
σ= (1)
I
Constr. Mater. 2024, 5, FOR PEER REVIEW
where σ—bending strength, M—maximum moment, I—moment of inertia, and C—centroid depth. 13
The results demonstrate the effect of fine waste plastic (WP) and waste glass (WG)
contents in concrete mixes on the flexural strength of the concrete. As illustrated in Figure 10,
when 20%20%
10, when of theoffine
the aggregate is replaced
fine aggregate by WG
is replaced byand
WGWP,andthe
WP,flexural strength
the flexural increases
strength in-
by 19.7%,
creases byfrom 12.46
19.7%, MPa
from to 15.52
12.46 MPa MPa.
to 15.52 MPa.

Figure10.
Figure 10. Example
Example of
of mean
mean flexural
flexural strength
strengthof
of C-25
C-25 concretes
concreteson
onday
day 28
28 with
with aa water–cement
water–cement ratio
ratio
of 0.4.
of 0.4.

This significant
This significant improvement
improvement in in flexural
flexural strength
strength suggests
suggests that
that incorporating
incorporating WG WG
and WP as partial replacements for traditional fine aggregates can enhance the mechanical
and WP as partial replacements for traditional fine aggregates can enhance the mechanical
properties
propertiesof ofconcrete.
concrete. The
The increase
increase in in flexural
flexural strength
strength can
canbe
beattributed
a ributed to to the
the improved
improved
bonding
bondingand anddistribution
distributionofofstress
stresswithin
within the concrete
the concrete matrix provided
matrix providedby bythethe
WGWG particles.
parti-
In contrast,
cles. the presence
In contrast, of WP might
the presence of WPcontribute to a lesser
might contribute toextent, indicating
a lesser that WG has
extent, indicating a
that
more
WG has pronounced effect on theeffect
a more pronounced flexural
on performance. These findings
the flexural performance. highlight
These findingsthe highlight
potential
the potential of utilizing waste materials in concrete production, promoting sustainable
construction practices while enhancing material properties.

3.7. Effect of Waste Plastics and Glass on Spli ing Tensile Strength
The results show that the use of optimal fine aggregate WP and WG contents in the
Constr. Mater. 2024, 4 593

of utilizing waste materials in concrete production, promoting sustainable construction

practices while enhancing material properties.

3.7. Effect of Waste Plastics and Glass on Splitting Tensile Strength

The results show that the use of optimal fine aggregate WP and WG contents in the
concrete mix reduced the splitting tensile strength of the mixture slightly.
Equation (2) gives the horizontal stress to which the element is subjected.

2P
σt = (2)
πLD
where P—the applied compressive load, L—the cylinder length, and D—the cylinder
diameter.
The split tensile strength of the control mix was 4.65 MPa, and the inclusion of waste
plastics and glass into the concrete resulted in a 4.3 MPa splitting tensile strength on the
28th day of curing, as shown in Figure 11. Therefore, the introduction of WP and WG
slightly decreased the splitting tensile strength compared to a plain concrete mix. The study
conducted in [54] concludes that concrete mortar could be made completely sustainable by
using recycled materials like glass, plastic, and recycled concrete, as well as micro-silica
Constr. Mater. 2024, 5, FOR PEER REVIEW 14
and fly ash, and that only 20% of the weight of cement could be used without lowering the
compressive and flexural strength of the concrete.

Figure11.
Figure 11. Example
Example of
of tensile
tensile strength
strength of
of C-25
C-25 concretes
concreteson
onday
day28
28with
withaawater–cement
water–cementratio
ratioof
of0.4.
0.4.

4.
4. Conclusions
Conclusions
The
The experimental
experimentalstudy
studyon onconcrete
concretesamples incorporating
samples plastic
incorporating and
plastic glass
and wastes
glass as
wastes
partial replacements for fine aggregate yielded the following key findings. Based
as partial replacements for fine aggregate yielded the following key findings. Based on on these
findings, the following
these findings, conclusions
the following can becan
conclusions drawn:
be drawn:
The
The optimal mix ratio of plastics to glasswaste
optimal mix ratio of plastics to glass waste was
was determined
determinedto to be
be 1:2.3.
1:2.3. This
This ratio
ratio
was found to provide the best balance between the structural integrity and recyclability
was found to provide the best balance between the structural integrity and recyclability of
the resulting material. Using this specific proportion ensures that the composite material
of the resulting material. Using this specific proportion ensures that the composite mate-
benefits from the desirable properties of both plastic and glass, making it suitable for
rial benefits from the desirable properties of both plastic and glass, making it suitable for
various practical applications.
various practical applications.
Incorporating waste plastics and glass into the concrete mix slightly reduced the
Incorporating waste plastics and glass into the concrete mix slightly reduced the
workability at water–cement ratios of 0.5 and 0.6. However, the workability remained
workability at water–cement ratios of 0.5 and 0.6. However, the workability remained un-
unaffected when the water–cement ratio was 0.4. Therefore, a water–cement ratio of 0.4 is
affected when the water–cement ratio was 0.4. Therefore, a water–cement ratio of 0.4 is
recommended to produce sustainable concrete from waste plastics and glass.
recommended to produce sustainable concrete from waste plastics and glass.
The investigation determined that the optimal replacement of fine aggregate with
The investigation determined that the optimal replacement of fine aggregate with
waste materials was 10%, comprising 7% waste glass and 3% waste plastic. However, to
waste materials was 10%, comprising 7% waste glass and 3% waste plastic. However, to
effectively utilize the waste materials, a 20% replacement—comprising 14% waste glass
effectively utilize the waste materials, a 20% replacement—comprising 14% waste glass
and 6% waste plastic—is a better option, as the mean compressive strength is almost
and 6% waste plastic—is a be er option, as the mean compressive strength is almost 25
MPa. This finding highlights a balanced approach to enhancing the sustainability of con-
crete production.
The compressive strength of concrete increases as the proportion of plastics in the
mix decreases and the amount of glass increases. This indicates that glass exerts a more
significant influence on the compressive strength compared to plastics.
Constr. Mater. 2024, 4 594

25 MPa. This finding highlights a balanced approach to enhancing the sustainability of

concrete production.
The compressive strength of concrete increases as the proportion of plastics in the
mix decreases and the amount of glass increases. This indicates that glass exerts a more
significant influence on the compressive strength compared to plastics.
In concrete mixes containing the optimal proportion of fine waste plastics and glass,
there was a significant enhancement observed in the flexural strength. However, there was
a slight decrease noted in the splitting tensile strength.
Overall, these findings highlight the potential for sustainable construction practices by
effectively integrating waste materials into concrete production processes.

Author Contributions: Conceptualization, A.M.L.; Formal analysis, A.M.L. and D.M.; Investigation,
A.M.L., D.M. and F.F.F.; Methodology, A.L and D.M.; Writing—original draft, A.M.L., D.M., F.F.F.,
G.U. and Y.T.B.; Writing—review and editing, A.M.L., F.F.F., G.U. and Y.T.B. All authors have read
and agreed to the published version of the manuscript.
Funding: This research received no external funding.
Data Availability Statement: The original contributions presented in the study are included in the
article, further inquiries can be directed to the corresponding author.
Conflicts of Interest: The authors declare no conflicts of interest.

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