**1. Introduction**

In proportion to the increasing urbanization in the world, raw material resources are decreasing and industrial wastes are increasing [1–11]. This situation causes serious environmental problems. Scientists who are aware of the problem offer various construction element suggestions in order to consume fewer raw materials and to permanently evaluate the wastes by the construction industry. Recycling waste materials to utilize in the construction projects reduces the use and costs of raw materials, even when more than one ton of

**Citation:** Çelik, A.˙ I.; Özkılıç, Y.O.; Zeybek, Ö.; Karalar, M.; Qaidi, S.; Ahmad, J.; Burduhos-Nergis, D.D.; Bejinariu, C. Mechanical Behavior of Crushed Waste Glass as Replacement of Aggregates. *Materials* **2022**, *15*, 8093. https://doi.org/10.3390/ ma15228093

Academic Editor: Alessandro P. Fantilli

Received: 13 October 2022 Accepted: 9 November 2022 Published: 15 November 2022

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

glass is recycled, 1.2 tons of raw materials can be saved [12]. In general, Europe's glass recycling rate is 71.48%, while Slovenia and Belgium have a high rate of 98%. In Turkey, around 9% of glass waste can be recycled. While 52.9% of glass containers produced in the United States are disposed of in landfills, 26.63% of glass can be recycled [13]. Recycling glass as glass again takes time and is costly. Because it is subjected to processes at 1200–1400 ◦C, in order to get rid of wastes such as dirt and rust from the final product, it needs to be melted again and a product can be obtained [14]. Reusing waste glass in the production of glass provides 5–10% economic benefits [15]. However, adding it as aggregate to structural products, such as concrete, may provide more economic benefits [16–18]. Many recycled materials are used in concrete by replacing them with cement or aggregates [19–21]. Recycled crushed glass is used in numerous studies around the world as a substitute for CA and FA for the development of sustainable concrete [22–24]. One of the most important of these waste materials is crushed waste glass (CWG) in aggregate size. The use of broken glass particles by substituting aggregates in concrete production is an important and interesting issue. Since glass does not change its structure when reprocessed, its chemical properties do not deteriorate and it is very easy to reprocess. Some glass products have a limited lifespan depending on their intended use. This increases the potential of broken waste glass particles. This recycling potential needs to be processed quickly [25]. In addition, the degradation rate of CWG is lower than industrial products, such as plastic, paper, and rubber. Therefore, the usage of broken glass fragments as a substitute for aggregates in concrete production will yield impressive consequences [26].

In recent years, much research was conducted on the mechanical properties of CWG added concretes. The CWG can be substituted for both fine and CAs [27]. The nature of glass reactivity causes significant effects when added to concrete. For example, some may cause excessive expansion in concrete when used as 100% of the total aggregate [28]. Studies show that with CWG aggregates, as the rate of change increases, the strength decreases faster. For example, in a study that used 15−60% substitution, it decreased the CS by 8% with the addition of 15% CWG, while it decreased the CS by 15% with the addition of 30% CWG. When this proportion is increased to 60%, the CS decreases by 49% [29]. Singh and Siddique, in their study, by replacing 10–50% CWG with FA, found that the strength decreased as the CWG proportion increased. However, when CWG was used with methacholine, they discovered that the strength improved as the methacholine addition increased [26]. This result shows that additional reinforcing materials can be added to increase the mechanical properties of the concrete whose environmental impact is increased with CWG. Harrison et al. used fine glass particles by substituting cement and FA in certain proportions in hopes of benefiting the mechanical properties of concrete. According to the consequences obtained, the cement preserves its mechanical properties when CWG particles are added up to 20%, but when the additions of 30% and above cause insufficient CaCO3 in the cement, the mechanical properties are adversely affected. It was also found that with the change in FA conservative, its mechanical properties are up to 20% substitution [27]. It was confirmed in some studies that the CS of concrete increases as the size of CWG particles is substituted with aggregate decreases. In their study, Shi et al. observed that finer glass particles improved the 28-day CS of concrete more than larger ones [30]. Chen et al., on the other hand, found that finer-ground glass particles performed better with similar behavior in 7-day and 28-day concrete CS [31]. Khmiri's et al. found that with up to 20% cement replacement, CWG ground up to 20 μm improved the late mechanical properties of concrete, while 40 μm CWG reduced the CS [32]. Letelier and Al-Hashmi found that 38 μm CWG had optimal mechanical properties at 20% cement substitute (by weight). In another study, it was revealed that 38 μm CWG had optimal mechanical properties at 20% cement replacement (by weight). It was determined that 10% and 30% substitutions gave consequences close to the reference sample [33]. Mostofinejad et al., examining 30% of cement by weight for ground CWG, found that the replacement had a strength reduction of 40% and 42%, respectively [34]. Tamanna et al. used 3000 μm CWG by replacing 20%, 40%, and 60% coarse sand. As a result of the 7, 28, and 56-day

compressive strength (CS) and flexural strength (FS) tests, they discovered that the 20% substitution gave good consequences, while the 40% and 60% substitution had negative effects on the CS and FS [35]. Penacho et al. investigated the effects of replacing 20%, 50%, and 100% CWG with FA on the mechanical properties of concrete. As a result of the analysis, he found that samples with higher sand substitution for fine CWG gave a greater strength increase. The increase in strength is related to the positive effect of pozzolanic reaction with the fine glass particles [36]. Lee et al. investigated the size effect of glass waste on the mechanical properties of concrete. As a result of the research, they found that the CS was better in samples consisting of particles smaller than 600 μm [37]. Corinaldesi et al. performed tests by replacing glasses with glass particles smaller than 36 μm, 36–50 μm, and 50–100 μm with aggregate. They performed compressive and FS tests at 180 days to study the influence of particle size. As a result of the observation, they found that the CS decreased at 30% FA substitution. However, at the 70% substitution proportion, they found that 50–100 μm samples showed milder increases over the reference sample [38]. Tejaswi et al. In a study they conducted, they found that replacing 20% by weight of CWG with FA gave a result close to the control sample, but replacing 10%, 30%, 40%, and 50% lowered the CS [39]. Batayneh et al. reported that replacing the CWG with the addition of fly ash increased the CS; however, they revealed that it did not change the splitting strength [40]. With a similar statement, Gerges et al. found that the rate of substitution of fine glass with sand had little effect on the compressive, splitting stress, or flexural strengths of concrete [41]. As a result of their study, Mohammed and Hama determined that when glass is added to concrete alone, it improves properties, such as CS, FS, and splitting tensile strength (STS). Compared to the reference sample, an increase of 14.12%, 1.7%, 6.01%, 52.63%, and 57.32% was observed in elastic modulus, energy capacity, and bond strength, respectively [42]. In a study by, Asa et al., it was found that the concrete to which 5% and 20% glass fragments were added led to a decrease of 3.8–10.6 percent and 3.9–16.4 percent, respectively, in the CS and tensile strength at the end of the 21st day, but the use of mineral additives changed the properties of the mixtures. They found that it improved after 7, 14, and 21 days of testing [25]. Walczak et al. used cathode ray tubes glass instead of sand, and they found that the compression strength increased about 16% and the bending strength increased about 14% [43].

Though several investigations were performed on this topic, as presented in above, there were changes in the consequences gained from the literature. Therefore, there is still a necessity to examine the mechanical productivity of concrete with the fractional replacement of CWG, and the perfect amount of it. For this purpose, an investigational study was performed on some investigation samples. The effects of different productionbased features of concrete with different amounts of crushed CWG as replacement of aggregates were studied. More importantly is that empirical equations are developed to predict the capacity of concrete with CWG, considering both the literature and the data obtained from the experimental study.

#### **2. Experimental Program**

To amount the mechanical belongings of the concrete with recycled CWG, different mixtures were cast. Eight different mixtures were chosen. Four of them were considered for FAs and rest of them were considered for CAs. Four different proportions of 10%, 20%, 40%, and 50% were selected (Table 1). CAs with a size of 5–13 mm were utilized while FAs with sizes of 0–4 mm were utilized. FA represents FA replacement and CA represents CA replacement. CWG was collected from Akcihan Glass, Istanbul, Turkey, involving a waste window glass (soda lime glass). The size of fine glass is a combination of glass with an equal amount of 1.7–4 mm and 100–200 micron, while the size of coarse glass is a combination of glass with an equal amount of 9–12 mm and 5–8 mm.


**Table 1.** Different mixtures of the concrete with recycled glass.

In the mixture, CEM 32.5 Portland cement was utilized. Water-to-cement proportion was selected as 0.5. The proportion of fine to CAs was selected as unity. The proportion of cement to total fine and CAs was selected as 0.2. Figure 1 shows slump test consequences of each mixture. The highest slump value was observed in the reference mixture. Adding recycled glass in concrete reduced slump value. Replacing aggregate resulted in a significant decrease in workability, especially after 20%. This is because glass particles have sharper and irregular geometric forms than sand particles, which can cause high friction, resulting in less fluidity [44]. Moreover, the binder effect of glass powder in FA replacement reduced workability even more than replacement of CA.

**Figure 1.** Slump test.
