Investigating the effects of steel slag powder on the properties of self-compacting concrete with recycled aggregates

Highlights

• This study investigated the relationships among multiple mechanical properties of SCRAC.

• Different replacement ratios of SSP had significant impacts on properties of SCRAC.

• SSP improved filling ability and passing ability of SCC, but adversely affected segregation resistance.

• The 10% replacement ratio of SSP was found achieving both superior mechanical properties and better durability.

Abstract

This study introduced both steel slag and recycled aggregate aiming to improve the sustainability performance of self-compacting concrete (SCC). The study focused on investigating the effects of steel slag powder on the properties of self-compacting concrete with recycled aggregate (SCRAC). Recycled aggregates were used to replace 30% of natural coarse aggregates by volume. The effects of various replacement ratios of steel slag powder (SSP) to Portland cement (i.e., 10%, 20%, 30%, 40%, and 50%) on the workability, mechanical properties, and durability of SCRAC were studied. The results showed that SSP improved filling ability and passing ability of SCC, but adversely affected the segregation resistance. It was found that 10% replacement ratio of SSP to ordinary Portland cement (OPC) in SCRAC showed superior mechanical properties and higher durability performance in resisting chloride penetration and carbonation.

Introduction

Self-compacting concrete (SCC) is a high-flow concrete with superior workability which is increasingly used in the construction industry with difficult casting conditions [1], [2], [3]. Compared to the conventional concrete, SCC could reduce labor input, decrease construction period, and improve the construction environment [4], [5]. However, in comparison with ordinary concrete, the SCC contains a greater amount of cementitious materials, high dosage of admixtures which provides the desired fluidity and viscosity. Considering this fact that production of one tone of Portland cement (PC) releases one tone of carbon dioxide (CO₂) to the atmosphere, the CO₂ emissions could be higher in the manufacturing of SCC if PC is used as the single cementitious material [6], [7]. Incorporating industrial wastes such as fly ash, steel slag and recycled aggregates in concrete mix design can improve the sustainability of concrete production by conserving energy and natural resources and reducing costs [8], [9], [10]. It has been observed that the SCC mixes containing low and intermediate percentage of recycled aggregates do not report any negative effect on the overall performance of SCC [11], [12].

Steel slag, as one type of solid wastes, is a by-product of the steel-making process [13]. It accounts for 10% to 15% of steel products in the manufacturing process by weight [14]. As one of the largest developing economies, China produced about 800 million tons of steel and 100million tons of steel slag in 2016. The production of steel slag is likely to increase due to the increased demand for steel. However, the utilization rate of steel slag is currently low in China, and a tremendous amount of steel slag is being dumped into landfills, occupying urban spaces and causing harms to the natural environment [15], [16].

Aiming to mitigate the environmental contamination, iron and steel enterprises in China have begun to seek an effective approach to reuse the steel slag. Researchers believe that a promising way to reuse steel slag would be to apply it in concrete mixture. Existing studies showed that steel slag contained somewhat similar chemical composition as cement did, and concrete made from steel slag could fill its internal voids, improve its interfacial bond between particles of binder, and reduce the hydration heat [17], [18], [19].

Despite of the ongoing research of applying steel slag in concrete production, its utilization together with recycled aggregates in SCC has not been sufficiently investigated. Due to the high water demand of recycled aggregate, it is expected that incorporation of recycled aggregates in SCC would cause adverse impacts on the fresh properties of SCC [20]. Diao et al. [21] utilized steel slag in SCC with acceptable fresh and mechanical properties to explore the feasibility of incorporating multiple waste streams. So far there are still limited researches in applying recycled aggregates in SCC.

In view of this, the primary goal of this paper is to explore the effects of steel slag powder on the properties of self-compacting concrete containing recycled aggregates. Five different SSP replacement ratios (i.e., 10%, 20%, 30%, 40%, and 50%) were studied. To evaluate the effects of SSP ratios on the workability of SCRAC, the filling ability, passing ability and segregation resistance of different mixture samples were tested. The compressive strength test, splitting tensile strength test and the static modulus of elasticity test were conducted to investigate the effects of replacement ratios of SSP on SCC’s mechanical properties. Moreover, the resistance chloride penetration and carbonization test were performed to evaluate the durability properties.