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Article

Eco-Friendly Lightweight Aggregate Concrete of Structural Grade Made with Recycled Brick Aggregate Containing Expanded Polystyrene Beads

by
Bogdan Rosca
Faculty of Civil Engineering and Building Services, Gh. Asachi Technical University, 700050 Iasi, Romania
Sustainability 2025, 17(7), 3050; https://doi.org/10.3390/su17073050
Submission received: 20 February 2025 / Revised: 19 March 2025 / Accepted: 26 March 2025 / Published: 29 March 2025
(This article belongs to the Section Sustainable Materials)
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Abstract

:
The quantity of construction demolition waste (CDW) has been increasing due to the demolition of many old buildings throughout the world. So far, all the statistics indicate that there is a very large generation of CDW, which increases annually. The increasing amount CDW in landfills will cause a scarcity of landfill space and will also increase pollution and cost due to transportation. Recycled brick aggregate concrete (RBAC) incorporating polystyrene (EPS) aggregate beads has emerged as an alternative lightweight material with numerous obvious sustainable benefits, suitable for a future circular economy. The goal of this paper is to assess the feasibility of obtaining lightweight aggregate concrete of structural grade with recycled brick aggregate (RBA) as a coarse aggregate and the incorporation of polystyrene beads in a certain percentage by conducting an experimental study on the dry and apparent density, compressive strength, split-tensile strength and elasticity modulus. In addition, the effects of the w/c ratio and cement content on these properties were studied to provide useful information for the performance optimization of this concrete with RBA and polystyrene (EPS) beads. The properties were investigated for two cement contents, 400 and 360 kg/m3, and two ratios between water and cement, 0.43 and 0.39, respectively. The RBAC mixtures containing EPS beads in 15%, 25% and 35% replacement percentages were evaluated through a comprehensive test program based on the European standards. The results showed that, in general, the use of polystyrene (EPS) beads decreased the mechanical properties of the recycled brick aggregate concrete; however, the outcome indicates the potential for producing lightweight concrete of different grades, including structural classes. It was found that the developed lightweight concrete presents a uniform distribution of the polystyrene granules in the hardened volume of concrete. Also, it was found that the recycled brick aggregate with a 16 mm maximum size did not negatively influence the uniform distribution of the EPS beads, avoiding concentrations of beads. With the increase in the percentage of EPS beads, the properties of the recycled brick aggregate concrete were found to be less sensitive to the water-to-cement ratio.

1. Introduction

The quantity of construction demolition waste (CDW) has been increasing due to the demolition of many old buildings throughout the world. This situation has caused serious environmental problems. In order to quantify the environmental impacts from CDW, public data about the quantity of CDW generated through demolition are available in countries like the USA, CE, China, Honk Kong, India, etc. In the United States, more than 145 mil. tons of CDW is generated each year, and this quantity is approximately one-third of the overall materials that are landfilled [1]. All over China, in the year 2013, more than one billion tons of CDW was created [2]. In Hong Kong, it was reported that CDW is nearly 28% of the solid waste in landfills [3]. It was also reported that there were about 1.53 mil. tons of CDW in 2015, increasing by 6.6% compared to 2014. Nearly 14.5 mil tons of CDW is created in India annually, which includes wastes like concrete and masonry [4], while in Malaysia, approximately 26,000 tons of CDW was reported to be created each day [5]. So far, all the statistics indicate that there is a very large generation of CDW, which increases annually. The increased use of CDW in landfills will cause a scarcity of landfill space and will also increase pollution and cost due to transportation. Therefore, utilizing waste masonry or waste bricks as an aggregate for making concrete is a good idea to avoid environmental problems.
In terms of sustainability, the reuse of waste clay bricks (WCB) could not only solve, in the proper way, the issues related to the environment but could also diminish the exploitation of natural resources, particularly in the countries where they are scarce [6]. Hence, studies on the reuse of waste clay bricks (WCB) are of great importance.
Numerous researchers have investigated the reuse of WCB and achieved notable results. A series of research studies focused on obtaining concrete by replacing natural coarse aggregate (NCA) with recycled brick aggregate (RBA), and the results showed that the mechanical properties of the obtained concrete were related to the aggregate replacement proportion and granular distribution [7,8,9,10,11,12]. Other studies have focused on the reuse of WCB as a fine aggregate in concrete [13,14,15]. A few researchers have conducted studies using WCB as fine and coarse aggregates in producing concrete [16,17,18,19].
An important issue related to recycled brick aggregate concrete (RBAC) is the higher absorption provided by the RBA compared to natural aggregate (NA), which can result in a sharp decrease in the workability depending on its replacement level. There are studies that attempted to solve this issue by using RBA in the saturated surface dry (SSD) state [6,7,17,20,21], while others attempted to bypass it by using supplementary water to obtain constant workability [8,11,13,15,18]. For concrete using additional water, this increased the water content and required a higher cement content, even without obtaining a higher strength. Within other studies, the authors used a higher water-to-cement ratio or water-reducing admixtures to increase the workability [9,14,22].
The compressive strength of recycled brick aggregate concrete (RBAC) is found to be smaller than that of conventional concrete depending on the replacement proportion of the natural aggregate with RBAC [7,9,14,21,22], the maximum aggregate size [13] and the use of RBAC as a coarse or fine aggregate or both [18]. Despite the reduction in compressive strength due to the embedding of RBA, for water-to-cement ratios lower than 0.45, the requirements on the structural grade are still accomplished, even for 100% replacements of the NCA with RBA. The compressive strength of RBAC containing fine brick aggregate has a higher rate of gaining strength between 28 and 90 days [14]. This effect can be explained by the puzzolanic action between its active silica and alumina and the hydration products of the cement.
Some researchers reported that, for replacement percentages of the NA up to 50% with RBA, the tensile strength, by the bending of concrete, was not significantly influenced [7].
Because the waste clay brick has a smaller bulk density compared to natural aggregate, the obtained concrete is lighter [18]; it has a lower apparent density, but at the same time, the workability is low, caused by the higher water absorption of the recycled brick aggregate [7].
For RBAC compared to normal concrete, the drying shrinkage is found to be higher. The utilization of recycled brick aggregate as a fine aggregate [14] and also as a coarse aggregate [18] led to higher shrinkage strains. This could be explained by a weaker impeding effect of RBA as compared to natural aggregate. On the contrary, there are research studies where a small drying shrinkage was reported with the embedding of 20% recycled brick as a fine aggregate [23]. This could be attributed to the curing effect of the recycled brick aggregate, whereby the additional water was adsorbed by the brick particles through pre-wetting, for example, it could maintain the state of moisture during hydration.
The thermal conductivity coefficient is found to be lower compared to normal concrete, caused mainly by the reduction in density [17].
The water absorption of RBAC was noted to be higher compared to normal concrete, caused by the higher porosity of RBA [8,18,19,20,21,22]. The use of RBA in concrete increases the water permeability depending on the dosage of RBA [11,18,22]. It can be underlined that, the higher the RBA content, the higher is the water permeability.
The apparent density of RBAC may decrease close to 2000 kg/m3 or even lower depending on the content of RBA. It is well known that the limit between normal and lightweight concrete is 2000 kg/m3 [24].
From the information presented above, it can be concluded that a serious drawback associated with the use of recycled brick aggregate in concrete is the large absorption of mixing water. This drawback of the RBA will influence the performance of RBAC, beyond the fact that it remains difficult to maintain a certain water content during casting. Therefore, it is important to ameliorate the concrete properties to ensure that the water absorption is diminished to admissible limits without the associated higher cement contents.
In the last three decades, various lightweight concretes were produced by replacing the natural aggregate, either partially or fully, with EPS aggregate depending on the strength and density required [25,26,27,28,29]. EPS lightweight concrete is an interesting building material that has gained the attention of researchers and the industry in the last decades because it is a lightweight and good thermal insulating material [30]. From these above-mentioned studies, it can be noted that the mechanical properties of concrete containing EPS beads are mainly related to the replacement ratio of the natural aggregate with EPS beads. There are studies where the strength of lightweight concrete containing EPS beads remained in the range of the structural grade [31,32,33,34]. Other factors of influence on the mechanical properties are the particle size of the beads [29,35,36] and the maximum size of the contained natural aggregate [34].
The performances of the EPS concrete were improved using supplementary cementitious material, like fly ash, silica fume or rice husk ash. Fly ash is a commonly used supplementary cementing material (SCM) because it not only enhances the concrete performance but also enhances sustainability for the cement and concrete industries. Some research evaluated EPS concrete containing fly ash up to 50% [25]. It was found that the absorption decreased, the chemical resistance was enhanced, and the compressive strength increased progressively up to 90 days.
Silica fume is currently used in EPS concrete in order to improve the final performance in both the fresh and hardened state [29,33,37,38].
For concrete containing conventional lightweight or recycled brick aggregate, the addition of EPS beads to replace the aggregate, coarse or fine, will further reduce the weight of the concrete but will very likely reduce the permeability and increase the resistance to environmental attack because of the closed cellular and inert nature of EPS beads [39,40].
Recent studies about lightweight concrete obtained with alternative sustainable materials, like natural pumice and plastic tube fibers, showed that it is possible to obtain concrete and structural members when such materials are used [41,42].
According to ACI 213R-14, lightweight concrete is divided into three categories as follows: lightweight concrete of structural grade having a compressive strength higher than 17 MPa, lightweight concrete of mild grade having a compressive strength range of 7 to 17 MPa, and lightweight concrete for isolation having a compressive strength lower than 7 MPa.
The purpose of this paper is to evaluate the feasibility of obtaining lightweight aggregate concrete of structural grade with RBA as a coarse aggregate and the incorporation of polystyrene beads in a certain percentage by conducting an experimental study on properties such as the apparent density, dry density, compressive strength, split-tensile strength and modulus of elasticity. In addition, the effects of the water-to-cement ratio and cement content on these properties are studied to provide useful information for the performance optimization of LWAC with RBA and polystyrene beads.
Combining recycled brick aggregate (RBA) with commercially available EPS rounded beads is a new approach to obtain a lightweight concrete of structural use, which might be relevant for the construction practice.
Recycled brick aggregate concrete (RBAC) incorporating EPS beads has emerged as an alternative lightweight material made with a renewable aggregate and with numerous obvious sustainable benefits, suitable for a future circular economy.

2. Materials and Methods

2.1. Materials

The recycled brick aggregate (RBA) was obtained from the demolition of a 90-year-old masonry structure. The masonry demolition waste pieces were crushed using a jaw crusher. Subsequently, the crushed material was sieved and split into fractions, and thus, coarse recycled brick aggregate (CRBA) was obtained. For the RBA, only 4/8 mm and 8/16 mm granular fractions were used as a coarse aggregate to manufacture the concrete mixtures (see Figure 1).
The fine aggregate was rounded river aggregate, with a maximum size of 4 mm, and the granular sizes of 0.02/0.5 mm, 0.5/1 mm, 1/2 mm and 2/4 mm were involved in the production of the concrete (see Figure 1). The grading of the aggregates, recycled and natural, is presented in Figure 2 and Table 1, respectively.
The physical properties of the aggregates, recycled and natural, are presented in Table 2.
In this research, in order to avoid the absorption problems that may be caused by the porous RBA, for all sizes of the recycled aggregate, the particles of the aggregate were cleaned in water and soaked for at least 24 h. Subsequently, in the concrete production process, the recycled brick aggregate was used in the saturated surface dry (SSD) state. The SSD state was obtained by placing the particles of aggregate on large cotton cloths, creating close contact between them, and applying horizontal circulating air provided by a fan. In addition, the particles of RBA were raked for many minutes with a hand hoe.
EPS beads of rounded shape with a size range of 3 to 6 mm, manufactured by a local Romanian commercial agent, were used (Figure 3). According to the certificate of conformity issued by the manufacturer, the apparent density of the beads was equal to 18 kg/m3, and they were covered with a bonding additive to reduce the hydrophobicity.
The cement utilized in this experimental research was CEM I 52.5N, with a Portland clinker content over 95%. This kind of cement, produced by the HOLCIM subsidiary factory from Medgidia, Romania, is free of supplementary cementing materials, the density of the cement is 3150 kg/m3, and it has a fineness of 4820 cm2/g. The water content was evaluated based on the selected w/c ratio in the mixture. The chemical composition of the cement is given in Table 3.

2.2. Concrete Mixture Proportions

The proportions of the concrete mixtures expressed by weight are presented in Table 4. Two series of mixtures were developed for different w/c ratios: 0.43 and 0.39 for series A and B, respectively. For each series, the cement content was changed from 400 kg/m3 to 360 kg/m3, and the coarse recycled aggregate was replaced in increasing volumes of 15% (E15), 25% (E25) and 35% (E35) with the EPS beads. For the same proportions of the mixture but without any substitution with EPS beads, the reference concrete (E0) was developed.
Two chemical admixtures conforming to EN 934 part2: 2001 were used as the reducing water admixture [43]. For the mixtures having a w/c ratio equal to 0.43 and 0.39, the superplasticizer SIKA BV540 and the high reducing water admixture Glenium 27 were used, respectively. The used amount of the chemical admixture was the lowest value provided by the manufacturer for each one.

2.3. Manufacture and Curing of Concrete

In this study, indications and procedures according to the EN 12390 were followed. For each mixture, the component materials were piled by weight. The mixtures were produced in the laboratory in batches in a tilting drum mixer having a volume capacity of 100 L. For all mixtures, the mixing procedure was the same. The recycled aggregate in the SSD state, followed by the natural aggregate and the EPS beads, were charged. All aggregate particles were mixed for at least 1 min. Next, the cement was charged and mixed with the aggregate for another minute. Subsequently, water was added, and the fresh mixture was mixed for at least 3 min to reach a uniform distribution of EPS beads. Afterwards, the chemical admixture was added, and the mixture was tilted for another 1 min. At the end of the mixing process, the aspect of the mixture showing a uniform distribution of the EPS beads was maintained.
All properties were determined on cubes and cylinders molded and demolded based on the information provided by the standard EN 12390-1 [44]. Thus, for all mixtures, the concrete of each batch was poured into cubic and cylinder steel molds. Cubes of 100 mm size and cylinders of 100 × 200 mm and 100 × 250 mm size were casted. The placement of concrete was performed in consecutive layers, and every layer was tapped with a rod, and afterwards, the molds were placed on a shaking table and vibrated. The cylinder and cubic specimens were demolded after 24 h, and subsequently, all specimens were kept in water at 20 ± 2 °C until the day of testing. The specimens were tested at 28 days after casting.
Considering three tests for each combination of w/c ratio, cement content and replacing percentage with EPS beads, a total number of 144 specimens were fabricated.

2.4. Methods

In this investigation, the performance of recycled brick aggregate concrete containing EPS beads was assessed by determining the properties in the fresh and hardened states. For all reported results, an average value of three specimens was calculated from the same casting batch. The concrete properties in fresh and hardened states were evaluated based on the European standards listed in Table 5.
In the fresh state, the workability was measured through the slump test, and the indications given by EN 12350-2 were followed [45].
The apparent and dry densities of the concrete were determined based on the information provided by EN 12390-7 [46]. At the standard age of 28 days, a series of three cube specimens was used to evaluate the apparent and dry densities. The apparent density was determined when the specimens were removed from water. The dry density was evaluated by measuring the volume and the corresponding dry mass, both being evaluated after drying at 105 ± 5 °C until a constant weight was maintained.
The compressive and split-tensile strength were determined based on the information provided by EN 12390-3 [47] and EN 12390-6 [48], respectively. The compressive strength was determined by testing cubes of 100 mm size. The tests were carried out using a hydraulic machine capable of developing compression loads at various stress rates. The machine was manufactured by Technotest from Italy in 2006 and is able to develop a maximum force of 3000 kN. The split-tensile strength was determined by testing cylinders of 100 mm diameter and 200 mm height using the same testing machine (see Figure 4). For the compression and split-tensile tests, the stress rate was established at 0.5 and 0.05 MPa/sec, respectively.
The modulus of elasticity was evaluated based on information comprised by the standard EN 12390-13 [49]. The stabilized modulus of elasticity Ecs was selected to be determined using method B provided by the standard. For the modulus of elasticity, cylinders of size 100 × 250 mm were used to be tested in the compression test using the same testing machine as mentioned before. Two digital dial gauges were used as deformation measuring devices. The precision of the devices was 0.001 mm, and they were manufactured by Italia Instruments (see Figure 5). The measuring devices were attached axially and centrally in the testing machine. Three cycles of loading were carried out, and the stabilized secant modulus of elasticity was determined on the third cycle. During all loading cycles, the stress rate was set to 0.6 MPa/sec.

3. Results and Discussion

3.1. Fresh Properties

Table 6 presents the results for the slump test. In general, the average value of the slump increased with the increase in the replacing percentage of the RBAC with EPS beads. For the same water-to-cement ratio, higher values of the slump were recorded for a cement content equal to 400 kg/m3 compared to a cement content equal to 360 kg/m3.
For concrete containing recycled brick aggregate, it is largely accepted that the workability is lower compared to conventional concrete with natural aggregate for the reason of the particle shape. In this study, the increase in slump is caused by the increasing volume of rounded EPS beads, which replace the angular particles of the brick aggregate.

3.2. Hardened Properties

3.2.1. Apparent and Dry Densities and Bead Distribution

In general, for concrete containing EPS beads, the density is a very important indicator that can influence many of the physical properties of the concrete, and it is strongly influenced by the volume of EPS beads utilized in the mixture.
Table 7 presents the test results for the apparent and dry densities in the hardened state of the RBAC with EPS beads. The table shows the apparent and dry density values evaluated at 28 days and relative values calculated as the ratio of the density of concrete with EPS beads to the corresponding reference concrete, i.e., concrete with no EPS beads.
It can be noted, in Table 7 and also Figure 6, that the highest values of apparent density of the RBAC with no EPS beads, i.e., reference concrete, range from 2050 to 2150 kg/m3 depending on the cement content and water-to-cement ratio. These values are less than the apparent density of plain concrete, but the obtained RBAC does not fall within the lightweight concrete category because the density is higher than 2000 kg/m3, according to ACI 213R-14. Also, in Table 7, it can be noted that the apparent density of the RBAC containing EPS beads in replacement percentages of 15%, 25% and 35% of the RBA varies from 1850 to 1500 kg/m3. The reason for this decrease is clearly the reduced density of the EPS beads compared to the recycled aggregate. From a density point of view, all obtained concretes containing EPS beads fall in the lightweight concrete category.
The relative value of the apparent density indicates that, by partially replacing the RBAC with EPS beads at replacement percentages equal to 15%, 25% and 35%, the decrease in density is 12%, 19% and 29%.
In Figure 6, it can be noted that, for both cement contents and all replacement percentages of aggregate, the apparent density is slightly higher for the lower w/c ratio, which is 0.39. This is explained by the higher density of the hardened cement paste, which occurs at the lower w/c ratios.
In Figure 7, as was expected, it can be noted that the apparent density is slightly higher for a cement content equal to 400 kg/m3 compared to 360 kg/m3.
The distribution of the EPS beads in the hardened RBAC is illustrated in Figure 8 on splitted specimens. It can be noted that the EPS beads are uniformly distributed in the volume of the test specimen, even for high substitution percentages of aggregate like 35%. Considering that, in most of the studies on EPS concrete presented in the Introduction, the maximum size of the natural aggregate is 8 or 10 mm, in this study, it can be remarked that the recycled brick aggregate with a 16 mm maximum size did not negatively influence the uniform distribution of the EPS beads, avoiding large concentrations of beads in between the largest particles of aggregate.
The lack of EPS segregation during vibration and the uniform distribution of EPS beads in the hardened concrete are assured through design of the mixture by selecting appropriate water-to-cement ratios, smaller than 0.45, where the mixing water content is low. In addition, the shape of the coarse aggregate, which is prone to being angular, contributed to the lack of segregation and uniform distribution of EPS beads in the mixture after vibration.

3.2.2. Compressive Strength

Table 8 presents the compressive strength of the RBAC with different replacement percentages of aggregate with EPS beads for two cement contents and w/c ratios. The table presents the compressive strength values evaluated at 28 days and relative values calculated as the ratio of the strength of concrete with EPS beads to the corresponding strength of the reference concrete, i.e., concrete with no EPS beads.
It can be noted, for a cement content equal to 400 kg/m3, by increasing the volume of EPS beads from 0 to 35% for the replacement of aggregate, for the two w/c ratios 0.43 and 0.39, the compressive strength decreases from 44.32 to 15.35 MPa and from 47.37 to 15.08 MPa, respectively. Also, for a cement content equal to 360 kg/m3, by increasing the volume of EPS beads from 0 to 35% for the replacement of aggregate, for the two w/c ratios 0.43 and 0.39, the compressive strength decreases from 43.35 to 14.75 MPa and from 46.60 to 13.75 MPa, respectively.
From a structural grade point of view, according to the classification provided by ACI 213R-14, for both the cement contents and w/c ratios considered in this study, the mixtures containing EPS beads in a percentage of replacement of 15% and 25% can be categorized as lightweight concrete of structural grade [50].
Figure 9 and Figure 10 present the variation in the compressive strength of the RBAC with various percentages of EPS beads for different cement contents and w/c ratios. As is expected, for a smaller water-to-cement ratio, the strength is higher for both cement contents.
It is obvious that the reduction in strength with the increasing volume of EPS beads is caused by the negligible strength and rigidity of the beads compared to the RBA. Moreover, the presence of the beads in hardened concrete leads to the development of a weak transition zone between the EPS aggregate and the hardened cement paste.
The variations in compressive strength with density for the RBAC containing EPS beads in different replacement percentages of aggregate are illustrated in Figure 11. As it can be seen, the compressive strength decreases with the decrease in the density of the RBAC concrete. In addition, it can be noted that the higher the replacement percentage with EPS beads, the lower is the gap between strengths for different w/c ratios. Therefore, the influence on strength of the w/c ratio, which is notable at replacement percentages lower than 25%, decreases for higher replacement percentages with EPS beads.
From a structural grade point of view, in Figure 11a, it can be observed that the developed lightweight concrete made with RBA containing EPS beads can provide approximately 30 MPa of strength and only 80% of the density of the reference concrete without EPS beads.
Considering that, in the mainstream of the technical literature, studies about lightweight concrete embedding recycled brick aggregate and EPS beads are not known, some comparisons can be made but must be made with studies on EPS concrete made with natural aggregate.
The results displayed in Figure 9 to Figure 11 are in accordance with other authors’ studies, but only a few of these studies present the strengths of EPS concrete that falls in the structural grade range. Thus, the reduction in the compressive strength by increasing the volume of EPS has been previously reported by Babu [25,35], Chen [26], Liu [36] and Nikbin [27].
Some studies present the variation in the compressive strength with density, where a linear relationship between the compressive strength and density of EPS concrete has been reported [39].

3.2.3. Split-Tensile Strength

The split-tensile strength of the RBAC containing EPS beads was determined, and the results are presented in Table 8. This table presents the split-tensile strength values determined at 28 days and relative values calculated as the ratio of the split-tensile strength of the concrete with EPS beads to the corresponding strength of the reference concrete, i.e., concrete with no EPS beads.
It can be noted that, for a cement content equal to 400 kg/m3, by increasing the volume of EPS beads from 0 to 35% replacement of aggregate, for the two w/c ratios 0.43 and 0.39, the split-tensile strength decreases from 3.98 to 1.87 MPa and from 4.46 to 1.95 MPa, respectively. Also, for a cement content equal to 360 kg/m3, by increasing the volume of EPS beads from 0 to 35% replacement of aggregate, for the two w/c ratios 0.43 and 0.39, the split-tensile strength decreases from 3.83 to 1.86 MPa and from 4.30 to 1.90 MPa, respectively.
Figure 12 illustrates the split-tensile strength of the RBAC for different cement contents and for two w/c ratios.
Figure 13 illustrates the split-tensile strength of the RBAC for two w/c ratios and for different cement contents.
The results displayed in Figure 12 to Figure 13 are in accordance with other authors’ studies, but only a few of these studies present the strengths of EPS concrete that falls in the structural grade range. Thus, the reduction in the split-tensile strength by increasing the volume of EPS has been previously reported by Babu [25,35], Chen [26], Liu [36] and Nikbin [27].
For the mixtures containing EPS beads, according to the results presented in Table 8, the compressive-to-tensile-strength ratio ranged between 8 and 10.

3.2.4. Modulus of Elasticity

It is well known that the rigidity of the internal materials from the structure of concrete plays an important role in the value of the modulus of elasticity. From the properties of polystyrene, it is known that the rigidity of this material is negligible; therefore, as is expected, the modulus of elasticity decreases as the volume of EPS beads increases.
Table 9 presents the elasticity modulus of the RBAC with different replacement percentages of aggregate with EPS beads for two cement contents and w/c ratios. The stabilized modulus of elasticity, according to the standard EN 12390-13, was determined. The table presents the values of the elasticity modulus evaluated at 28 days and relative values calculated as the ratio of the elasticity modulus of concrete with EPS beads to the corresponding reference concrete, i.e., concrete with no EPS beads.
It can be noted, for a cement content equal to 400 kg/m3, by increasing the volume of EPS beads from 0 to 35% replacement of aggregate, for the two w/c ratios 0.43 and 0.39, the elasticity modulus decreases from 28.40 to 13.50 MPa and from 33.02 to 13.78 MPa, respectively. Also, for a cement content equal to 360 kg/m3, by increasing the volume of EPS beads from 0 to 35% replacement of aggregate, for the two w/c ratios 0.43 and 0.39, the elasticity modulus decreases from 27.40 to 13.00 MPa and from 31.86 to 13.27 MPa, respectively.
Figure 14 and Figure 15 present the variation in elasticity modulus of the developed RBAC with different percentages of EPS beads for two cement contents and w/c ratios. It can be noted that, with the increase in the replacement percentage, the elasticity modulus decreases. As is expected, for the lower w/c ratio, higher values of the moduli of elasticity were obtained.
Moreover, in Figure 14, it can be noted that the higher the replacement percentage with EPS beads, the lower is the gap between the elasticity moduli for different w/c ratios. From Figure 15, it can be observed that, for a higher cement content, higher values were obtained. From the results presented above, it can be concluded that the highest elasticity modulus decrease in the concrete was 58%. This is in accordance with the results reported by Dixit et al. [38], who manufactured polystyrene concrete containing 0–45 vol% of EPS and reported a reduction in the modulus of elasticity of around 68.9%.
As is shown in Figure 14 and Figure 15, the stabilized modulus of EPS concrete displays an almost linear decrease with the increasing replacement percentage of EPS. Compared with the results from other authors, the results extracted from Figure 14 and Figure 15, which are previously mentioned, are in accordance with the results published by Nikbin and Golshekan [27].

3.3. Practical Feasibility of RBAC with EPS Beads

The impacts of different types of lightweight aggregate combined with EPS have not been fully investigated so far. According to the obtained results in this study, combining EPS beads with recycled brick aggregate has a great potential in obtaining lightweight concrete of structural grade. The current study is devoted to obtaining RBAC containing EPS beads that are commercially available worldwide, which, by default, are rounded in shape, the size varies between 3 mm and 6 mm, and frequently, the beads are treated against hydrophobicity by the manufacturer. In this condition, the applicability of the study is enhanced, and it offers a practical solution that is readily available for practitioners.
The main drawback of the classical polystyrene concrete, which combines a natural aggregate and EPS beads, remains the segregation and volume concentration of the EPS beads. This drawback has a significant impact on the mechanical performance of the polystyrene concrete. From this perspective, combining EPS beads with RBA particles, which are more angular in shape compared to a natural aggregate, leads to a uniform distribution of the beads, avoiding volume concentrations despite a quite long vibration time of the concrete (see Figure 8). This is a real advantage compared to classical polystyrene concrete. Such performance regarding the segregation and volume concentration is attained using a quite high volume of coarse particles of RBA.

4. Conclusions

In the present research, we developed an eco-friendly lightweight concrete of structural grade made with recycled brick aggregate containing EPS beads in different replacement percentages, and the physical and mechanical properties in the fresh and hardened states were investigated. The properties were investigated for two cement contents, 400 and 360 kg/m3, and two w/c ratios, 0.43 and 0.39, respectively. The conclusions that can be drawn are as follows:
  • The use of EPS beads together with RBA as an aggregate in concrete can substantially contribute to equilibrating the demand of renewable resources, leading to a beneficial step forward towards sustainability, economy and solid waste management.
  • In general, the use of EPS beads decreased the mechanical properties of the recycled brick aggregate concrete; however, the results showed the potential for producing lightweight concrete of different grades, with densities between 1500 and 1800 kg/m3.
  • Recycled brick aggregate concrete as a lightweight concrete of structural grade was obtained by replacing the recycled coarse aggregate with EPS beads in percentages no higher than 25% for two different w/c ratios, 0.43 and 0.39, respectively. For the smallest w/c ratio, with the increase in the replacement percentage to 35%, the compressive strength falls into the range corresponding to lightweight concrete of medium strength, according to ACI 213R-14ACI.
  • The developed lightweight concrete presents a uniform distribution of the EPS beads in the hardened concrete, avoiding volume concentrations.
  • The influence of the w/c ratio on the compressive strength, which is notable at replacement percentages lower than 25%, decreases for higher replacement percentages with EPS beads, for example, 35% in this study.
  • With the increase in the cement content from 360 kg/m3 to 400 kg/m3, for all the determined physical and mechanical properties, higher values were recorded; in addition, the slump increased.
  • The values of the w/c ratios used in this experimental study may be considered moderate and low–moderate, denoting that higher concrete strengths are possible to obtain for lower ratios, but a lower workability is expected, which can be counteracted by using the chemical admixtures in a higher content.
  • With the increase in the replacement percentage of recycled aggregate with EPS beads from 0% to 35%, the slump of the concrete increased; the cause of such an improvement in the slump was the rounded shape of the EPS beads.
  • With the increase in the replacement percentage of recycled aggregate with EPS beads from 0% to 35% for the two w/c ratios 0.43 and 0.39, the highest decreases in the apparent density, compressive strength, split-tensile strength and elasticity modulus were 29%, 68%, 57% and 58%, respectively.
  • For the replacement percentages of 15% and 25%, the highest decreases in the compressive strength were 34% and 51%, respectively.
Based on this study, eco-friendly lightweight concrete of structural grade made with recycled brick aggregate and EPS beads can be readily obtained by the practitioners. However, the use of this type of concrete to reinforce concrete members must be further investigated, exploring the long-term durability properties and reinforcement–concrete bond behavior.

Funding

This research was funded by National Research Grants of the TUIASI, GnaC2023_257/2024 and The APC was funded by National Research Grants of the TUIASI.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author(s).

Conflicts of Interest

The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

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Figure 1. Granular sizes of the coarse RBA and fine natural aggregate used for the manufacture of the RBAC mixes.
Figure 1. Granular sizes of the coarse RBA and fine natural aggregate used for the manufacture of the RBAC mixes.
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Figure 2. Granular size distribution of aggregate.
Figure 2. Granular size distribution of aggregate.
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Figure 3. EPS beads used in the manufacture of RBAC.
Figure 3. EPS beads used in the manufacture of RBAC.
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Figure 4. Test setup for determination of split-tensile strength.
Figure 4. Test setup for determination of split-tensile strength.
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Figure 5. Test setup for determination of modulus of elasticity.
Figure 5. Test setup for determination of modulus of elasticity.
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Figure 6. Apparent density of RBAC with different percentages of EPS: (a) Apparent density for cement content 400 kg/m3 and w/c ratio 0.43 and 0.39; (b) Apparent density for cement content 360 kg/m3 and w/c ratio 0.43 and 0.39.
Figure 6. Apparent density of RBAC with different percentages of EPS: (a) Apparent density for cement content 400 kg/m3 and w/c ratio 0.43 and 0.39; (b) Apparent density for cement content 360 kg/m3 and w/c ratio 0.43 and 0.39.
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Figure 7. Apparent density of RBAC with different percentages of EPS: (a) Apparent density for water/cement ratio 0.43 and cement content of 400 and 360 kg/m3; (b) Apparent density for water/cement ratio 0.39 and cement content of 400 and 360 kg/m3.
Figure 7. Apparent density of RBAC with different percentages of EPS: (a) Apparent density for water/cement ratio 0.43 and cement content of 400 and 360 kg/m3; (b) Apparent density for water/cement ratio 0.39 and cement content of 400 and 360 kg/m3.
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Figure 8. Appearance of section of the RBAC on splitted specimens: (a) 15% EPS replacement of the RBA; (b) 25% EPS replacement of the RBA; (c) 35% EPS replacement of the RBA.
Figure 8. Appearance of section of the RBAC on splitted specimens: (a) 15% EPS replacement of the RBA; (b) 25% EPS replacement of the RBA; (c) 35% EPS replacement of the RBA.
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Figure 9. Compressive strength of RBAC with different percentages of EPS: (a) Compressive strength for cement content 400 kg/m3 and w/c ratio 0.43 and 0.39; (b) Compressive strength for cement content 360 kg/m3 and w/c ratio 0.43 and 0.39.
Figure 9. Compressive strength of RBAC with different percentages of EPS: (a) Compressive strength for cement content 400 kg/m3 and w/c ratio 0.43 and 0.39; (b) Compressive strength for cement content 360 kg/m3 and w/c ratio 0.43 and 0.39.
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Figure 10. Compressive strength of RBAC with different percentages of EPS: (a) Compressive strength for w/c 0.43 and cement content 400 and 360 kg/m3; (b) Compressive strength for w/c 0.39 and cement content 400 and 360 kg/m3.
Figure 10. Compressive strength of RBAC with different percentages of EPS: (a) Compressive strength for w/c 0.43 and cement content 400 and 360 kg/m3; (b) Compressive strength for w/c 0.39 and cement content 400 and 360 kg/m3.
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Figure 11. Relation between density and compressive strength of RBAC containing EPS beads: (a) relation for cement content 400 kg/m3 and w/c 0.43 and 0.39; (b) relation for cement content 360 kg/m3 and w/c 0.43 and 0.39.
Figure 11. Relation between density and compressive strength of RBAC containing EPS beads: (a) relation for cement content 400 kg/m3 and w/c 0.43 and 0.39; (b) relation for cement content 360 kg/m3 and w/c 0.43 and 0.39.
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Figure 12. Split-tensile strength of RBAC for different cement contents: (a) Split-tensile strength for 400 kg/m3 and 0.43 and 0.39 w/c ratio; (b) Split-tensile for 360 kg/m3 and 0.43 and 0.39 w/c ratio.
Figure 12. Split-tensile strength of RBAC for different cement contents: (a) Split-tensile strength for 400 kg/m3 and 0.43 and 0.39 w/c ratio; (b) Split-tensile for 360 kg/m3 and 0.43 and 0.39 w/c ratio.
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Figure 13. Split-tensile strength of RBAC for different water/cement ratios: (a) Split-tensile strength for 0.43 w/c and cement content 400 and 360 kg/m3; (b) Split-tensile strength for 0.39 w/c and cement content 400 and 360 kg/m3.
Figure 13. Split-tensile strength of RBAC for different water/cement ratios: (a) Split-tensile strength for 0.43 w/c and cement content 400 and 360 kg/m3; (b) Split-tensile strength for 0.39 w/c and cement content 400 and 360 kg/m3.
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Figure 14. Elasticity modulus of RBAC with different EPS percentages for different cement contents: (a) Elasticity modulus for 400 kg/m3 and 0.43 and 0.39 w/c ratio; (b) Elasticity modulus for 360 kg/m3 and 0.43 and 0.39 w/c ratio.
Figure 14. Elasticity modulus of RBAC with different EPS percentages for different cement contents: (a) Elasticity modulus for 400 kg/m3 and 0.43 and 0.39 w/c ratio; (b) Elasticity modulus for 360 kg/m3 and 0.43 and 0.39 w/c ratio.
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Figure 15. Elasticity modulus of RBAC for different water/cement ratios: (a) Elasticity modulus for 0.43 w/c and cement content 400 and 360 kg/m3; (b) Elasticity modulus for 0.39 w/c and cement content 400 and 360 kg/m3.
Figure 15. Elasticity modulus of RBAC for different water/cement ratios: (a) Elasticity modulus for 0.43 w/c and cement content 400 and 360 kg/m3; (b) Elasticity modulus for 0.39 w/c and cement content 400 and 360 kg/m3.
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Table 1. Details on grading.
Table 1. Details on grading.
Sieve Size (mm)Fine AggregateSieve Size (mm)Coarse Aggregate
% Passing by MassNatural Sand% Passing by MassCRBA
410020100
2321697.5
122.80868
0.5013.60446
0.254.40--
0.0630--
CRBA is coarse recycled brick aggregate.
Table 2. Physical properties of the recycled and natural aggregates.
Table 2. Physical properties of the recycled and natural aggregates.
PropertyCRBA 1Sand
Specific gravity (SSD) [kg/m3]21402600
Bulk density [kg/m3]10401730
24 h water absorption [%]14.41.2
1 CRBA is coarse recycled brick aggregate.
Table 3. Chemical composition of cement CEM I 52.5N.
Table 3. Chemical composition of cement CEM I 52.5N.
OxideCaOSiO2Al2O3Fe2O3MgONa2OK2OSO3LOI
[%]60.1221.786.564.132.080.360.422.162.39
Table 4. Mixture proportions of RBAC with EPS beads.
Table 4. Mixture proportions of RBAC with EPS beads.
SeriesMixW/CCEM
[kg/m3]		EPS
[%]		RBA
[kg/m3]		Sand
[kg/m3]		Water
[L/m3]		SP
[%]
A
(w/c = 0.43)		A400E00.4340007438171700.006
A400E15400155807611700.006
A400E25400254727231700.006
A400E35400353636851700.006
A360E036007768521530.006
A360E15360156067941530.006
A360E25360254927541530.006
A360E35360353797151530.006
B
(w/c = 0.39)		B400E00.3940007618361540.010
B400E15400155947781540.010
B400E25400254837401540.010
B400E35400353727011540.010
B360E036007918701390.010
B360E15360156188101390.010
B360E25360255027701390.010
B360E35360353877301390.010
Table 5. Tests used in evaluating the fresh and hardened concrete.
Table 5. Tests used in evaluating the fresh and hardened concrete.
Property Under EvaluationStandard
Slump testEN 12350-2 [45]
Apparent density of hardened concreteEN 12390-7 [46]
Compressive strengthEN 12390-3 [47]
Split-tensile strengthEN 12390-6 [48]
Modulus of elasticityEN 12390-13 [49]
Table 6. Slump values of the recycled brick aggregate concrete (RBAC).
Table 6. Slump values of the recycled brick aggregate concrete (RBAC).
MixEPS Replacement in AggregateVolume of EPS in MixSlump
[%][%][mm]
A400E00030
A400E151510.2550
A400E252517.08100
A400E353523.91130
A360E00020
A360E151510.6945
A360E252517.8270
A360E353524.95100
B400E00025
B400E151510.4940
B400E252517.4880
B400E353524.4795
B360E00020
B360E151510.9140
B360E252518.1860
B360E353525.4580
Table 7. Apparent and dry densities of the recycled brick aggregate concrete (RBAC).
Table 7. Apparent and dry densities of the recycled brick aggregate concrete (RBAC).
MixEPS Replacement in AggregateVolume of EPS in MixApparent
Density		Relative
Value		Dry
Density
[%][%][kg/m3] [kg/m3]
A400E00021001.002010
A400E151510.2518500.881770
A400E252517.0817000.811630
A400E353523.9115000.711440
A360E00020501.001970
A360E151510.6918000.881730
A360E252517.8217000.831640
A360E353524.9514700.721420
B400E00021501.002080
B400E151510.4918700.871810
B400E252517.4817500.821700
B400E353524.4715300.711490
B360E00021001.002040
B360E151510.9118500.881800
B360E252518.1817000.811660
B360E353525.4515000.721460
Table 8. Strength properties of the RBAC.
Table 8. Strength properties of the RBAC.
MixEPS Replacement in AggregateVolume of EPS in MixCompressive
Strength		Relative
Value		Split-Tensile StrengthRelative
Value
[%][%][MPa] [MPa]
A400E00044.321.003.981.00
A400E151510.2530.370.693.050.77
A400E252517.0825.640.582.800.70
A400E353523.9115.350.351.870.46
A360E00043.351.003.831.00
A360E151510.6928.700.662.900.75
A360E252517.8221.260.492.480.64
A360E353524.9514.250.331.860.48
B400E00047.371.004.461.00
B400E151510.4933.620.713.200.72
B400E252517.4829.250.623.170.70
B400E353524.4715.080.321.950.43
B360E00046.601.004.301.00
B360E151510.9131.000.663.100.72
B360E252518.1824.560.532.640.61
B360E353525.4514.750.321.900.44
Table 9. Modulus of elasticity of the recycled brick aggregate concrete (RBAC).
Table 9. Modulus of elasticity of the recycled brick aggregate concrete (RBAC).
MixEPS Replacement in AggregateVolume of EPS in MixModulus of Elasticity
Ecs		Relative
Value
[%][%][GPa]
A400E00028.401.00
A400E151510.2523.400.82
A400E252517.0820.100.71
A400E353523.9113.500.47
A360E00027.401.00
A360E151510.6922.400.81
A360E252517.8218.300.67
A360E353524.9513.000.47
B400E00033.021.00
B400E151510.4924.630.75
B400E252517.4820.720.63
B400E353524.4713.780.42
B360E00031.861.00
B360E151510.9123.580.74
B360E252518.1818.870.60
B360E353525.4513.270.41
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Rosca, B. Eco-Friendly Lightweight Aggregate Concrete of Structural Grade Made with Recycled Brick Aggregate Containing Expanded Polystyrene Beads. Sustainability 2025, 17, 3050. https://doi.org/10.3390/su17073050

AMA Style

Rosca B. Eco-Friendly Lightweight Aggregate Concrete of Structural Grade Made with Recycled Brick Aggregate Containing Expanded Polystyrene Beads. Sustainability. 2025; 17(7):3050. https://doi.org/10.3390/su17073050

Chicago/Turabian Style

Rosca, Bogdan. 2025. "Eco-Friendly Lightweight Aggregate Concrete of Structural Grade Made with Recycled Brick Aggregate Containing Expanded Polystyrene Beads" Sustainability 17, no. 7: 3050. https://doi.org/10.3390/su17073050

APA Style

Rosca, B. (2025). Eco-Friendly Lightweight Aggregate Concrete of Structural Grade Made with Recycled Brick Aggregate Containing Expanded Polystyrene Beads. Sustainability, 17(7), 3050. https://doi.org/10.3390/su17073050

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