Concrete Containing Waste Glass as an Environmentally Friendly Aggregate: A Review on Fresh and Mechanical Characteristics

The safe disposal of an enormous amount of waste glass (WG) in several countries has become a severe environmental issue. In contrast, concrete production consumes a large amount of natural resources and contributes to environmental greenhouse gas emissions. It is widely known that many kinds of waste may be utilized rather than raw materials in the field of construction materials. However, for the wide use of waste in building construction, it is necessary to ensure that the characteristics of the resulting building materials are appropriate. Recycled glass waste is one of the most attractive waste materials that can be used to create sustainable concrete compounds. Therefore, researchers focus on the production of concrete and cement mortar by utilizing waste glass as an aggregate or as a pozzolanic material. In this article, the literature discussing the use of recycled glass waste in concrete as a partial or complete replacement for aggregates has been reviewed by focusing on the effect of recycled glass waste on the fresh and mechanical properties of concrete.


Introduction
Glass is one of the world's most diverse substances because of its substantial properties, such as chemical inertness, optical clarity, low permeability, and high authentic strength [1][2][3]. The usage of glass items has greatly increased, leading to enormous quantities of WG. Globally, it is estimated that 209 million tons of glass are produced annually [4][5][6]. In the U.S., according to the Environmental Protection Agency (EPA) [7][8][9], 12.27 million tons of glass were created in 2018 in municipal solid waste (MSW), as shown in Figure 1, most of which were containers for drinking and food. Furthermore, in 2018, the EU generated 14.5 million tons of glass package wastes [10][11][12]. The quantity of generated WG will increase due to the increasing demand for glass components [13][14][15][16].
Recycling and reducing waste are key parts of a waste-management system since they contribute to conserving natural resources, reducing requests for waste landfill space, and reducing pollution of water and air [17,18]. According to Meyer [19], by 2030, the EU zero-waste initiative estimates that improvements in resource efficiency throughout the chain could decrease material input requirements by 17% to 24%, satisfying the demand WG into useful glass particles for wall-panel production. Subsequently, a signif study was conducted in order to use recycled glass for fine or coarse aggregate in m and concrete, because of the good hardness of the glass [14,28,29]. This study aims viewing the possibilities of utilizing WG in concrete as a partial or full replacemen fine or coarse aggregates in order to give practical and brief guidance on recycling using WG [30][31][32][33].

Research Significance
Besides the above-mentioned dangers of WG and the need to recycle it econom and environmentally, this research explores the source of WG as well as its physica chemical characteristics. In addition, this study aims to review the literature that disc the use of recycled WG in concrete as a partial or complete alternative to aggregat focusing on the effect of this waste on the fresh and mechanical properties of concre order to demonstrate the possibilities of using recycled WG in concrete and to pro practical and brief guidance. Furthermore, we are establishing a foundation for f study on this material and describing research insights, existing gaps, and future res goals. In fact, innovative options for recycling WG must be developed. One significant option is to use WG for construction materials [23]. The recycling of WG not only decreases the demand for landfill sites in the building sector but also significantly helps in decreasing the carbon footprint and saving resources [24][25][26]. In 1963, Schmidt and Saia [27] performed the first research on the use of WG for building materials. The authors recycled WG into useful glass particles for wall-panel production. Subsequently, a significant study was conducted in order to use recycled glass for fine or coarse aggregate in mortar and concrete, because of the good hardness of the glass [14,28,29]. This study aims at reviewing the possibilities of utilizing WG in concrete as a partial or full replacement for fine or coarse aggregates in order to give practical and brief guidance on recycling and using WG [30][31][32][33].

Research Significance
Besides the above-mentioned dangers of WG and the need to recycle it economically and environmentally, this research explores the source of WG as well as its physical and chemical characteristics. In addition, this study aims to review the literature that discusses the use of recycled WG in concrete as a partial or complete alternative to aggregates by focusing on the effect of this waste on the fresh and mechanical properties of concrete in order to demonstrate the possibilities of using recycled WG in concrete and to provide practical and brief guidance. Furthermore, we are establishing a foundation for future study on this material and describing research insights, existing gaps, and future research goals.

Chemical Properties of Glass
Glass exists in various colors and types, with various chemical components. Tables 1 and 2 show the chemical compositions of different colors and types of typical glass, respectively.

Physical and Mechanical Properties of Glass
The physical and mechanical properties of crushed WG are listed in Tables 3 and 4, respectively.

Workability
There are two parallel points of view on the workability of WG-containing concrete. A review of past studies on the impact of WG aggregates on the mixes of workability  Table 5. It can be noticed that various research investigations have shown that the mixing of WG increases workability. They connected this beneficial impact of WG on the workability to the weaker cohesive between the cement mortar and the smooth surfaces of waste glass [48][49][50][51][52]. The smooth surface and low absorption capacity of WG are also important factors in increasing workability [53,54]. For example, Ali and Al-Tersawy [55] substitute fine aggregate in self-compacting concrete (SCC) mixes with recycled WG at levels of 10% to 50% by volume. Constant content of water-cement ratio and various superplasticizer doses have been used. They stated that slump flow increased by 2%, 5%, 8%, 11%, and 85%, with the incorporating of 10%, 20%, 30%, 40% and 50% of WG, respectively. In addition, Liu, Wei, Zou, Zhou and Jian [56] substitute fine aggregate in ultra-high-performance concrete (UHPC) mixes with recycled liquid crystal display (CRT) glass at levels of 25% to 100% by volume. Constant content of water-cement ratio and various superplasticizer (SP) doses have been used. Moreover, they stated that flowability increased by 11, 14, 16, and 12 mm, compared to the control sample, incorporating 25%, 50%, 75%, and 100% WG, respectively. Enhancing the workability by including WG is a benefit of utilizing this recycled material [57][58][59][60]. There is potential to utilize glass to create HPC in which high workability is necessary. In addition, WG can be used to boost workability rather than employing admixtures such as HRWR or superplasticizers [61][62][63][64].
Contrastingly, some studies have stated that including waste glass into the mixes lowered workability. Nevertheless, such a decrease has been associated with sharp edges, higher glass particle aspect ratio, and angular form, with obstruction of the movement of particles and cement mortar [65][66][67][68][69][70][71]. For example, Wang [72] substitutes fine aggregate in liquid crystal display glass concrete (LCDGC) mixes with recycled LCD at levels of 20% to 80% by volume. Various contents of w/c ratio (0.38-0.55) and various superplasticizer doses have been used. The author stated that slump flow decreased by 4%, 7%, 19%, and 26%, incorporating 20%, 40%, 60%, and 80% of WG, respectively, for w/c of 0.44. In addition, Arabi, Meftah, Amara, Kebaïli and Berredjem [73] substitute coarse aggregate in SCC mixes with recycled windshield glass at levels of 25% to 10% by volume. Various contents of w/c ratio (0.60-0.69) and various superplasticizer doses have been used. They stated that slump flow decreased by 3%, 8%, 9%, and 11%, incorporating 20%, 40%, 60%, and 80% of WG, respectively. According to Rashad [61], the optimal content of glass waste to achieve good workability is 20%.  Where: SCGC is self-compacting glass concrete; SCC is self-compacting concrete; HPGC is high performance recycled liquid crystal glasses concrete; UHPC is ultra-high performance concrete; LCDGC is liquid crystal display glass concrete; LCD is liquid crystal display; CRT is cathode ray tube; WG is waste glass; PVC is polyvinyl chloride; SP is superplasticizer; HRWRA is a high-range water-reducing agent; WR is water-reducing; AE is air-entraining; SF is silica fume; F.A. is fly ash; GBFS is granulated blast furnace slag; MK is metakaolin; SH is sodium hydroxide solution; SS is sodium silicate solution; F.A is fine aggregate; C.A is coarse aggregate; vol. is replacing by volume; wt. is replacing by weight.

Bulk Density
Past studies on the impact of WG aggregates on the bulk density, which are summarized in Figure 2, revealed that the majority of studies showed that incorporating glass waste into mixtures reduces density. This decrease can be ascribed to the lesser density of WG compared to natural aggregate [42,65,93,94], as well as the lower specific gravity [43,66,87,93,95]. For example, Taha and Nounu [65] substitute fine aggregate in waste-glass concrete (WGC) mixes with recycled soda-lime glass at levels of 50% to 100% by volume. They stated that the fresh density of WG concrete mixes reduced by 1% and 2% incorporating 50% and 100% of WG, respectively. This density drop might be realized as one benefit of using this material in concrete for engineering purposes [96][97][98][99].
On the other hand, Liu, Wei, Zou, Zhou and Jian [56] stated that concrete of 10 to 50% WG had a fresh density greater than reference. The authors substitute F.A in UHPC mixes with recycling CRT glass at levels of 25% to 100% by volume. They stated that the fresh density of waste-glass concrete mixtures increased by 1% 2.5%, 3.5%, and 6%, incorporating 25%, 50%, 75%, and 100% of WG, respectively. The authors attributed the reason to the fact that the density of CRT glass (2916 kg/m 3 ) was larger than that of fine aggregate (2574 kg/m 3 ) [100][101][102][103][104].

Compressive Strength
By reviewing past studies on the impact of WG aggregates on the compressive strength of waste-glass concrete, summarized in Table 6, it can be noticed that most studies shown that incorporating glass waste into concrete reduces compressive strength. The researchers ascribed this behavior to (i) the sharp edges and smooth particle surfaces, leading to a poorer bond between cement mortar and glass particles at the interfacial transition zone (ITZ) [14,40,42,43,55,66,87,90,108,109]; (ii) increased water content of the glass aggregate mixes due to the weak ability of WG to absorb water [43,110]; and (iii) the cracks caused by expanding stress formed by the alkali-silica reaction produced from the silica in WG [40]. For example, Park, Lee and Kim [89] substitute fine aggregate in WGC with recycled green WG at levels of 30% to 70% by weight. They stated that the compressive strength of concrete decreased by 3%, 13%, and 18%, incorporating 30%, 50%, and 70% of WG, respectively. In addition, Terro [48] noted that concrete, which contains up to 25% of WG, showed compressive strength values greater than the reference, whereas concrete with a substitution level of over 25% declined in compressive strength.
In order to better understand the impact of glass waste on the properties of the wasteglass concrete [111][112][113][114]. Omoding, Cunningham and Lane-Serff [115] investigated the concrete microstructure via SEM by replacing between 12.5-100% of the coarse aggregate with green waste glass with a size of 10-20 mm. The authors stated (i) that there is a weak connection between the waste glass and the cement matrix. This is because of a reduction in bonding strength between the waste glass and the cement paste because of the high smoothness of waste glass, consequently resulting in cracks and poor adherence between waste glass and cement paste; and (ii) as the content of waste glass increases, the proportion of cracks and voids increases in the concrete's matrix.

Compressive Strength
By reviewing past studies on the impact of WG aggregates on the compressive strength of waste-glass concrete, summarized in Table 6, it can be noticed that most studies shown that incorporating glass waste into concrete reduces compressive strength. The researchers ascribed this behavior to (i) the sharp edges and smooth particle surfaces, leading to a poorer bond between cement mortar and glass particles at the interfacial transition zone (ITZ) [14,40,42,43,55,66,87,90,108,109]; (ii) increased water content of the glass aggregate mixes due to the weak ability of WG to absorb water [43,110]; and (iii) the cracks caused by expanding stress formed by the alkali-silica reaction produced from the silica in WG [40]. For example, Park, Lee and Kim [89] substitute fine aggregate in WGC with recycled green WG at levels of 30% to 70% by weight. They stated that the compressive strength of concrete decreased by 3%, 13%, and 18%, incorporating 30%, 50%, and 70% of WG, respectively. In addition, Terro [48] noted that concrete, which contains up to 25% of WG, showed compressive strength values greater than the reference, whereas concrete with a substitution level of over 25% declined in compressive strength.
In order to better understand the impact of glass waste on the properties of the wasteglass concrete [111][112][113][114]. Omoding, Cunningham and Lane-Serff [115] investigated the concrete microstructure via SEM by replacing between 12.5-100% of the coarse aggregate with green waste glass with a size of 10-20 mm. The authors stated (i) that there is a weak connection between the waste glass and the cement matrix. This is because of a reduction in bonding strength between the waste glass and the cement paste because of the high smoothness of waste glass, consequently resulting in cracks and poor adherence between waste glass and cement paste; and (ii) as the content of waste glass increases, the proportion of cracks and voids increases in the concrete's matrix.
However, some studies have stated that waste glass increases mechanical strength. This increase is primarily realized because of the surface texture and strength of the waste glass particles compared to natural sand [116][117][118] and the pozzolanic reaction of waste glass aggregate [119][120][121]. For example, Jiao, Zhang, Guo, Zhang, Ning and Liu [81] substitute fine aggregate in UHPC with recovered WG at levels of 25% to 100% by weight. They stated that the compressive strength of concrete increased by 2%, 17%, 34%, and 20%, incorporating 25%, 50%, 75%, and 100% WG, respectively.
Regarding the influence of WG color on properties, some studies have stated that the color of WG did not produce any noticeable variation in strength [89,122]. On the contrary, Tan and Du [66] claimed that clear waste glass showed less strength.  Changed by +20%, +15%, −10%, and −35%, respectively.
Where: SCGC is self-compacting glass concrete; SCC is self-compacting concrete; HPGC is high performance recycled liquid crystal glasses concrete; HSPC is high-strength pervious concrete; UHPC is ultra-high performance concrete; LCDGC is liquid crystal display glass concrete; LCD is liquid crystal display; CRT is cathode ray tube; WG is waste glass; PVC is polyvinyl chloride; SP is superplasticizer; HRWRA is a high-range water-reducing agent; WR is water-reducing; AE is air-entraining; SF is silica fume; F.A. is fly ash; GBFS is granulated blast furnace slag; MK is metakaolin; SH is sodium hydroxide solution; SS is sodium silicate solution; F.A is fine aggregate; C.A is coarse aggregate; vol. is replacing by volume; wt. is replacing by weight.

Splitting Tensile Strength
Past studies on the impact of WG aggregates on the splitting tensile strength of wasteglass concrete, which are summarized in Table 7, revealed that incorporating glass waste into concrete reduces tensile strength. Similarly, as in compressive strength, studies have attributed the main reason for this behavior to the poor bond between cement paste and glass particles at the ITZ. For example, Wang [72] substitutes fine aggregate in liquid crystal display glass concrete (LCDGC) with recycled LCD glass at levels of 20% to 80% by volume. The author stated that splitting tensile strength of concrete decreased by 1%, 7%, 8%, and 9%, incorporating 20%, 40%, 60%, and 80% of WG, respectively, for w/c of 0.44. Moreover, Ali and Al-Tersawy [55] substitute fine aggregate in self-compacting concrete (SCC) with recycled WG at levels of 10% to 50% by volume. They stated that tensile strength of wasteglass concrete decreased by 9%, 15%, 16%, 24%, and 28% incorporating 10%, 20%, 30%, 40%, and 50% of WG, respectively [129][130][131][132].
In contrast, Jiao, Zhang, Guo, Zhang, Ning and Liu [81] indicated that concrete of 25% to 100% WG had a tensile strength greater than reference. The authors substitute fine aggregate in ultra-high-performance concrete (UHPC) with recycled WG at levels of 25% to 100% by weight. They stated that the splitting tensile strength of concrete increased by 1%, 3%, 11%, and 7%, incorporating 25%, 50%, 75%, and 100% of WG, respectively. The author attributed the reason to the effect of using steel fibers.  Decreased by 22%, 39%, 39%, and 44%, respectively.
Where: UHPC is ultra-high-performance concrete; LCDGC is liquid crystal display glass concrete; LCD is liquid crystal display; CRT is cathode ray tube; WG is waste glass; SP is superplasticizer; HRWRA is a high-range water-reducing agent; SF is silica fume; F.A. is fly ash; F.A is fine aggregate; C.A is coarse aggregate; vol. is replacing by volume; wt. is replacing by weight.

Flexural Strength
The flexural strength of waste-glass concrete shows comparable tendencies to its compressive strength and tensile strength. Most of the research revealed that introducing WG aggregates reduced flexural strength. However, other research showed that flexural strength increased when WG was included [134][135][136]. For instance, Kim, Choi and Yang [79] substitute fine aggregate in WGC with recycled CRT glass at levels of 50% to 100% by volume. They stated that flexural strength of concrete decreased by 9% and 14%, incorporating 50% and 100% of WG, respectively, for w/c of 0.45. On the contrary, Jiao, Zhang, Guo, Zhang, Ning and Liu [81] substitute fine aggregate in UHPC with recovered WG at levels of 25% to 100% by weight. They stated that flexural strength of concrete increased by 2%, 1%, 5%, and 1%, incorporating 25%, 50%, 75%, and 100% of WG, respectively.
Moreover, it can be concluded that the discrepancy between studies may be related to the type, size, and source of WG used in the mixtures. The mineral composition varies as the type of glass changes. Therefore, changing the mechanisms of interaction with binders in concrete, in turn, affects the properties. Table 8 presents the outcomes of various studies on the flexural strength of waste-glass concrete.  Where: SCGC is self-compacting glass concrete; SCC is self-compacting concrete; UHPC is ultra-high-performance concrete; LCDGC is liquid crystal display glass concrete; LCD is liquid crystal display; CRT is cathode ray tube; WG is waste glass; SP is superplasticizer; HRWRA is a high-range water-reducing agent; WR is water-reducing; AE is air-entraining; SF is silica fume; F.A is fine aggregate; C.A is coarse aggregate; vol. is replacing by volume; wt. is replacing by weight.

Modulus of Elasticity (MOE)
The modulus of elasticity of concrete (MOE) depends on the normal and lightweight aggregates elasticity modulus, cement matrix, and their relative ratios in the mixes [39]. In general, the incorporation of WG aggregates into concrete increases the modulus of elasticity [72,84]. For instance, Steyn, Babafemi, Fataar and Combrinck [82] substitute fine aggregate in WGC with recovered WG at levels of 15% to 30% by volume. They stated that MOE of concrete increased by 1%, and 7%, incorporating 15% and 30% of WG, respectively. In addition, Omoding, Cunningham and Lane-Serff [115] substitute coarse aggregate in glass aggregate concretes with recycled WG at levels of 12.5% to 100% by volume. They stated that MOE of concrete increased by 2% to 4% for a replacement rate of 12.5% to 50%, then decreased by 3% to 9% for replacement ratios above 50% [137,138].
However, some studies have stated that including WG decreases the MOE of concrete. For instance, Ali and Al-Tersawy [55] substitute fine aggregate in SCC with recovered WG at levels of 10% to 50% by volume. They stated that MOE of concrete decreases by 2%, 8%, 9%, 12%, and 13%, incorporating 10%, 20%, 30%, 40% and 50% of WG, respectively. Figure 3 presents the outcomes of various studies on the MOE of WG concrete. where: SCGC is self-compacting glass concrete; SCC is self-compacting concrete; UHPC is ultrahigh-performance concrete; LCDGC is liquid crystal display glass concrete; LCD is liquid crystal display; CRT is cathode ray tube; WG is waste glass; SP is superplasticizer; HRWRA is a high-range water-reducing agent; WR is water-reducing; AE is air-entraining; SF is silica fume; F.A is fine aggregate; C.A is coarse aggregate; vol. is replacing by volume; wt. is replacing by weight.

Modulus of Elasticity (MOE)
The modulus of elasticity of concrete (MOE) depends on the normal and lightweight aggregates elasticity modulus, cement matrix, and their relative ratios in the mixes [39]. In general, the incorporation of WG aggregates into concrete increases the modulus of elasticity [72,84]. For instance, Steyn, Babafemi, Fataar and Combrinck [82] substitute fine aggregate in WGC with recovered WG at levels of 15% to 30% by volume. They stated that MOE of concrete increased by 1%, and 7%, incorporating 15% and 30% of WG, respectively. In addition, Omoding, Cunningham and Lane-Serff [115] substitute coarse aggregate in glass aggregate concretes with recycled WG at levels of 12.5% to 100% by volume. They stated that MOE of concrete increased by 2% to 4% for a replacement rate of 12.5% to 50%, then decreased by 3% to 9% for replacement ratios above 50% [137,138].

Data Availability Statement:
The data used to support the findings of this study are included in the article.