1. Introduction
In the utilization of industrial residues as construction raw materials, the concrete industry can play an important role in sustainable development, leading to considerable environmental benefits. Generally, aggregates (coarse and fine) occupy about 60–85% of the total volume of hardened concrete [
1]. Aggregates are important constituents in the concrete composite that help to improve the various properties of concrete, including reducing the shrinkage and providing workability, volume stability, strength, and durability to the concrete [
2]. In the numerous countries of South Asia, the concrete industry mostly depends on burnt clay brick aggregate (BA) due to the shortage of natural stones [
3]. The production process of BA increases CO
2 in the air, resulting in a large negative environmental impact and risk to human life. Though crushed stone aggregates are used in the concrete industry due to rapid urbanization, they are mostly imported from abroad, thereby, increasing the cost of concrete production. Due to the aforementioned issues, indeed, it is necessary to find possible alternative construction raw materials that can be used as coarse and fine aggregates in concrete construction works [
4,
5,
6].
Steel slag is a byproduct of the steelmaking process which is produced during the separation of the molten steel from impurities in the steelmaking furnace, and it is used as coarse aggregate in concrete. It was found that steel slag aggregate (SSA) has superior physical and mechanical properties as well as lower carbon footprint and reduced negative environmental effects [
7,
8]. The compressive strength of concrete containing steel slag at 28 days was about 35% higher than the reference concrete [
9]. The incorporation of different replacement percentages (15%, 25%, 50%, 75%, and 100%) of natural stone aggregate by SSA increased compressive and flexural strength, while it reduced the chloride ion permeability from 40% to 70% compared to concrete made with natural stone aggregate [
10]. Similarly, research demonstrated that the physical and mechanical properties of concrete made of slag aggregate were higher as compared to natural aggregate [
11]. Conversely, the reduction in workability was observed for concrete containing SSA compared to natural aggregate.
Netinger et al. [
12] investigated the mechanical properties and corrosion resistance of concrete made with SSA. It was found that SSA can be used in concrete since it provides acceptable mechanical properties and no risk of corrosion of reinforcement. It was found that the carbonation treatments can significantly improve the strength and volume stability of concrete made with carbonated granulated steel slag aggregate [
13]. Abu-Eishah et al. [
14] observed that the concrete made with steel SSA provides high-strength compared to similar conventional concrete mixtures, which could be due to the strong bond between the cement/mortar matrix and SSA. It has been observed that concrete made with SSA decreased the workability of fresh concrete; it was claimed that SSA particles were angularly resulting in a reduction of the flowability of concrete [
13]. Similarly, Qasrawi [
15,
16] observed that the addition of SSA decreased the workability of concrete and produced an unacceptable flow when more than 50% SSA were used. The reduction in a slump of concrete containing SSA was also observed by Sheen et al. [
17].
Several studies have been carried out to investigate the mechanical performance of concrete made with SSA, but few focused on durability (e.g., porosity). To the authors’ knowledge, there seems to be no published work on concrete made with induction furnace SSA as a replacement of BA. This induction furnace slag is used mainly for landfills and sometimes as an alternative aggregate in road construction, which is not very common due to lack of research data. The lack of research data, limited information, and knowledge on the mechanical and durability performances of concrete made with SSA as a replacement for BA motivate this research work. Within this context, comprehensive experimental studies were conducted on the possibility of using induction furnace steel slag as coarse aggregate replacement for BA. This is with the goal to reduce the consumption of industrial-made brick (reduce CO2) and natural aggregate which is mainly imported from abroad (reduce the cost of concrete and obtain a sustainable construction material). The aim of this research work is to investigate the physical, mechanical (i.e., compressive and splitting tensile strength), length change, and durability (porosity) performances of concrete made with nine different replacement percentages (0%, 10%, 20%, 30%, 40%, 50%, 60%, 80%, and 100% by volume of BA) of BA by induction furnace SSA. To gain a deeper understanding of the role of SSA on the performance of concrete, the relation between strength (compressive and tensile) and porosity of concrete mixes was discussed. Additionally, the chemical composition of aggregate through X-ray fluorescence (XRF) analysis was determined and microstructural analysis using scanning electron microscopy (SEM) of aggregates and concrete was performed.
4. Concluding Remarks
In this paper, the effect of steel slag aggregate (SSA) as a substitute for conventionally used brick aggregate (BA) on the physical, mechanical, and durability (i.e., porosity) performances of concretes was investigated. It is worth noting, however, that many studies have been conducted on the mechanical properties of concrete, while comparatively, few published data are available on the durability (e.g., porosity) as well as length change. To this end, nine concrete mixes made with different percentage replacements of BA by SSA were studied. The main findings of the influence of SSA on the physical, mechanical, and porosity of concrete can be summarized as follows:
The use of SSA as a replacement for BA in concrete shows significantly higher compressive and tensile strength, which was 73% higher when BA was fully replaced by SSA.
Lower workability was noticed for the concrete made with SSA than BA, which could be attributed to the higher rough surface texture and higher angularity of SSA than BA as well as better interlocking, which reduces the mobility of fresh concrete.
The concrete made with SSA exhibited higher expansion than the concrete made BA.
A significantly lower porosity was observed for the concrete made with SSA than BA. The maximum decrease in porosity was observed when BA was fully replaced by SSA, and the decrease was 45.80% lower than BA concrete.
A satisfactory relationship between strength (compressive and tensile) and porosity was observed, which is consistent with the literature.
SEM images showed that SSA was denser and has a stronger ITZ, which leads to the higher strength of concrete. By contrast, BA has more voids and cracks on aggregate as well as at the ITZ, which explains the lower strength of this concrete.
From the experimental results of the nine mixes, this study reveals that SSA can be used as a full replacement for BA since SSA is denser, less porous, higher angularity, and has excellent surface roughness, which provides better mechanical and durability performances. Furthermore, SSA concrete provides environmental solutions by reducing the dumping problem, economical, conservation of natural aggregate, and sustainable green construction material since burning brick produces a lot of CO2.
Future research should focus on utilizing other industrial by products and sustainable technologies such as 3D concrete printing [
41,
42,
43] without compromising the mechanical properties required for civil applications.