A study of characteristics of man-made lightweight aggregate and lightweight concrete made from expanded polystyrene (eps) and cement mortar

: This research investigated the feasibility of using waste-expanded polystyrene (EPS) and mortar to produce lightweight aggregate (LWA). The EPS extracted from the leftover backing waste was crushed into beads using an electric grinder and mixed in three di ﬀ erent proportions with two types of mortars (with and without a superplasticizer). Physical property tests such as loose bulk density and water absorption were carried out for the LWA. Also, the compressive strength of the manufactured lightweight aggregate concrete (LWAC) was determined, and failure modes were discussed. The results indicate that using the EPS is e ﬀ ective for LWA. The loose bulk density is obtained at a range from 588 to 790 kg/m 3 , which meets the requirements of the American society for testing and materials C330 speci ﬁ cation of LWA. For water absorption, the value obtained ranges from 6.45 to 14.05%, slightly higher than the normal aggregate due to the voids in the LWA. When using LWA containing a super-plasticizer to produce LWAC, the compressive strength was higher than the concrete with LWA without a superplasticizer. The highest compressive strength for LWAC was 21 MPa.


Introduction
Lightweight concrete (LWC) can be described as a kind of concrete. That includes expanding matters, increasing the mixture's volume while giving additional qualities such as reducing elements' self-weight [1]. The dry density of the LWC is 300-1,840 kg/m 3 , making it 87-23% lighter than traditional concrete [2].
Due to the advantageous properties of LWC, including low density, good thermal insulation, and fire resistance, it has been widely studied as a structural and nonstructural member [3].
The types of LWC are categorized based on production techniques [4]. The first type is called no fines LWC, which is produced by eliminating the fine portion of aggregates [5]. The second type is aerated concrete, which generates air bubbles in the concrete structure by adding chemical additives [6]. The third type is called lightweight aggregate concrete (LWAC), which is usually produced by replacing the conventional aggregate phase fully or partially with lightweight aggregates (LWAs) such as pumice, perlite [7][8][9], expanded shale [10][11][12], aggregate concrete made from foam, and ordinary Portland cement [13] and expanded clay [3,14] into the mixture.
LWAs are even natural or artificial [15]; using natural LAWs such as expanded clay instead of conventional aggregate increases the water demand owing to its highly porous structure, causing difficulty in producing an appropriate, consistent mixture [16]. In addition, certain artificial coarse lightweight is obtained through heat treatment, which requires a sintering temperature between 1,000 and 1,200°C. As a result of this high-temperature process, the production process consumes higher fuel costs.
Consequently, the overall construction cost will increase [13]. Therefore, making LWAs that do not consume energy in the production process is very useful. Nevertheless, the most significant advantage of using LWAG is preserving the environment when some materials are reused from industrial wastes or leftovers of product packaging materials [17].
Expanded polystyrene (EPS) is the most popular backing and insulation material; nevertheless, it becomes a waste once used [18]. Statistics show that 14 million tons of EPS is produced yearly, 2.3 million tons of EPS waste is landfilled in the USA, and 300,000 tons of EPS is dumped in the UK yearly [4]. Therefore, EPS is a municipal solid waste (MSW) that requires a sustainable recycling strategy to reduce its negative environmental impact. Several suggested recycling methods include volume reduction, heat treatment (thermal recycling), and chemical recycling [19]. Among (MSWs), the recycle of EPS using the methods mentioned above is high expensive because of its huge air volume which makes it inconvenient through transport [20]. In addition, energy consumption is used by thermal recycling [17].
From a construction point of view, EPS concrete is classified as an artificial concrete with ultra-lightweight [21]. So, it is advantageous to utilize EPS to produce lightweight structures. In addition, it has a nonabsorbent, closed cellular structure, making it a suitable solution to produce adequate consistency without increasing the water demand of the concrete mix. The previous studies introduced EPS concrete by mixing EPS beads randomly in the concrete structure to produce LWC [22,23]. This technique causes several disadvantages during mixing, such as flouting EPS beads; furthermore, the strength reduction increases with the rise of EPS aggregate percentage in the concrete mixture [15,22,24]. This article introduces a novel concept using EPS beads to produce a lightweight man-made aggregate. This concept overcomes the lack of mixing control and high absorption problem and guarantees better strength than other techniques. Also, the produced concrete's density still meets the standard's requirements.

Cement
Ordinary Portland cement was used throughout this research. The required quantity was brought to the laboratory and stored in a dry place.

Sand
Silica sand was used in this study for two purposes. The first was to produce the concrete, while the second was to produce the LWA using the sand that passes from Sieve No. 16 (1.18 mm).

EPS
The EPS has been prepared in the laboratory using waste material from the market. The EPS was crushed into small granules using an electric grinder to facilitate its addition to cement mortar and obtain a homogenous mixture to produce the LWA ( Figure 1).

Water
In this study, ordinary potable water was used to produce the cement mortar and LWA for curing purposes.

Superplasticizer concrete admixture
In this study, a high-performance superplasticizer concrete admixture is called SikaViscoCrete-5930. This admixture is a third-generation superplasticizer for concrete and mortar. It complies with the superplasticizer specifications in ASTM-C-494 Types G and F and BS EN 934 Part 2: 2001.

Preparation of LWAs
In this study, two types of LWAs were prepared: (1) LWA was made without adding superplasticizer (Groups A, B, and C) to the mortar. The mortar consists of sand with cement at a ratio of 1:1. These ingredients were mixed to obtain a homogeneous mixture and then water was added to the cement with a water-to-cement (W/C) ratio of 0.5. The EPS was then added and mixed at different percentages of EPS/mortar volume (Table 1, Figure 2). The mixture is formed into a spherical LWA and left for 4 to 5 h; curing stage was attained by immersing the aggregates in the water ( Figure 4). (2) LWA was made by adding superplasticizer to the mortar before adding EPS (Groups D and E) ( Figure 3). The amount of the added superplasticizer was 0.25% of the cement weight (Table 1). Again, the LWA was left for 4 to 5 h, the curing stage was achieved with the same previous procedure ( Figure 4).

Concrete mix
The concrete was conducted by a concrete mix ratio of 1: 1.5: 4 and a W/C ratio of 0.7 with the two types of aggregates (

Physical and mechanical properties 2.4.1 Loose bulk density test of aggregates
In this study, the size of LWA being about 20-25 mm, loose bulk density was determined according to ASTM C29/C29M as the aggregate was below the maximum size, 25 mm. The mass of non-compacted aggregates needed to fill a container with a unit volume after aggregates were batchstored according to volume is known as the loose bulk density. By using the shoveling method, loose bulk density was calculated [25].

Water absorption test
The absorption of water defines as the rise in the mass of LWA because of the penetration of water into the pores of the particles, but not including water adhering to the surface of the particles. It is conducted to calculate the change in aggregate mass due to water absorbed in the pore that is present in the aggregate [26]. According to ASTM C127, 2 kg of LWA is washed and dried before the test sample is placed in the oven at 105 ± 5°C for 1-3 h. Then, let LWA cools down at room temperature. Then the LWA was submerged at room temperature for 24 ± 4 h. The test sample was removed from the water and wiped until it became  saturated and surface dry. Then the LWA will be weighed and recorded as B. Afterward, LWA is placed in the oven at ± 105 5°C for 24 ± 4 h and weighed and recorded as A. Water absorption can be calculated by knowing the difference in weight of LWA.

Compressive strength
The compressive strength cube test was carried out following the specifications in American society for testing and materials. All cube specimens were marked on the surface and placed in a water-curing tank. The cube of the test was placed centrally on the lower plate of the test machine, with the rough top surface facing outward. The maximum load that could be applied before the cube failed was noted.
3 Results and discussion 3.1 Loose bulk density of LWA Figure 5 shows the various values of the loose bulk density of LWA depending on its components. The bulk density of LWA value was in the range of 588-790 kg/m 3 ; these values are below the maximum value of 880 kg/m 3 permitted [27]. As can be seen, for groups A, B, and C, the density decreased with the increase in EPS content. When the ratio of EPS to mortar in group A is 0.5:1, the density is 790 kg/m 3 , and when the ratio of EPS to mortar in group C becomes 1.5:1, the density is equal to 645 kg/m 3 . Group B's density is between the previous densities because it contains more EPS than group A and less than group C. The same behavior is noted with groups D and E, but with a more decrease in density of the same amount of EPS compared with the previous three groups; this can be explained as a result of changing work steps and because of the use of a superplasticizer. The presence of a superplasticizer made the mixing of EPS with mortar an easy process and did not require high energy, which led to the retention of EPS at    most of its original volume and was not subjected to compression and decrease in volume as found in groups A, B, and C (Figures 6 and 7). Figure 8 shows the various values of water absorption of LWA depending on its components. It is clear that for all groups A, B, C, D, and E, the water absorption decreased with an increased EPS content. Water absorption in group A was 14.05%, which decreased in groups B and C to 13.15 and 11.43%, respectively, because the EPS does not absorb water.

Absorption of LWA
The same behavior is noted with groups D and E but with a more decrease in water absorption of the same amount of EPS than with the previous three groups. This can be explained as a result of the use of a superplasticizer. The presence of a superplasticizer led to the retention of EPS for most of its original volume and was not subjected to a decrease in volume as in groups A, B, and C. In addition, the presence of a superplasticizer led to a self-compacting process in the mortar. As a result, an additional decrease in mortar voids was observed. Figure 9 shows the correlation between the density and water absorption of LWA. As shown in Figure 9, the relationship between density and absorption is a direct correlation. This means that the density drop necessarily leads to a decrease in absorption and vice versa. This result can be explained by the fact that LWAs' density has decreased due to an increase in the proportion of EPS in their composition; as EPS does not absorb water, the LWAs' water absorption has decreased.     Figure 8 shows the various values of the density of concrete made of LWA depending on its components. The figure illustrates that all concrete mixtures met the requirements for LWC in terms of density. The density ranged from 1,788 kg/m 3 of group C-B to 1,590 kg/m 3 of group C-E. Also, the figure shows that the presence of a superplasticizer significantly impacts concrete density. For the same EPS content (groups C-B and C-D) and (groups C-C and C-E) the presence of superplasticizer made the density of group C-D less than the density of group C-B by 100 kg/m 3 and group C-E less than group C-C by 138 kg/m 3 . In addition, group C-D's density is less than group C-C's, although it contains the least amount of EPS of the two groups. Figure 9 shows the compressive strength of different concrete mixtures. In general, the compressive strength of concrete decreased with an increase in the EPS portion in the aggregate.

Compressive strength of concrete
This behavior was the same for the two types of aggregates. Also, the compressive strength obtained from concrete made of LWA with superplasticizer was greater than that obtained from the other type. For example, the compressive strength of groups C-D and C-E at 28 days was 21 and 16.6 MPa, which was higher than all other types.

Correlation between density and
compressive strength of concrete Figure 10 shows the relationship between the density and compressive strength of concrete. The figure shows the decreased compression strength and density for the same aggregate type. The figure also shows that when comparing the concrete made of aggregate types D and E with concrete made of aggregate types A, B, and C, we note that despite the first group having a lower density than that of the second group, these groups show higher compressive strength. This is due to the superplasticizer's effect, which makes the aggregate structure stiffer, reducing the voids.    of concrete with LWA made without superplasticizer occurred in the aggregate, not the mortar. However, the failure occurred for mortar and not aggregate in concrete with LWA with a superplasticizer. This shows that working on a new design to produce a more powerful mortar will increase the compressive strength of concrete made of aggregate content superplasticizer.

Conclusion
In this research, a variety of LWAs have been made. All aggregate types are based on EPS. The aggregates were used in the fabrication of LWC samples. A series of tests were conducted on LWAs and LWC. From the current research and with reference to the discussions of the results obtained from the currently conducted experiment, the following conclusions may be drawn to be adopted for further studies: (1) The use of EPS in the fabrication of coarse aggregates has significantly impacted the production of aggregates with a low density (LWAs). This effect increased when using superplasticizers. (2) Increasing the amount of EPS mixed with the mortar produces lighter aggregates but is weaker when compressive strength is considered. (3) Increasing the amount of EPS mixed with the mortar produces lighter aggregates and less water absorbable due to a decrease in the aggregate's porosity. (4) When the aggregate used in the concrete fabrication contains more EPS, the result will be that the concrete is lighter, has less compressive strength, and is less absorbent to water. (5) When a certain amount of EPS is used in producing LWAs, adding the superplasticizer to the production of the aggregates leads to the production of aggregates and concrete that are lighter, stronger, and less water absorbent than that produced without the addition of superplasticizer.

Conflict of interest:
The authors state no conflict of interest.
Data availability statement: Most datasets generated and analyzed in this study are comprised in this submitted manuscript. The other datasets are available on a reasonable request from the corresponding author with the attached information.