The influence of steel slag with variable particle size distribution on the workability and mechanical properties of concrete

The present research investigated the influence of steel slag (SS) with variable particle size on the workability and mechanical properties of concrete. Different SS size ranges (0-15 μm, 15-30 μm, 30-45 μm and 45-80 μm) were obtained by sieving and then were characterised by a laser particle size analyser and a scanning electron microscope (SEM). The slump, compressive strength, pore structures and thermal analysis were used to evaluate the effect of the SS particle size on cement and concrete properties. The experimental results showed that finer SS (0-15 μm and 15-30 μm) resulted in negative effects on the workability, while 30-45 μm and 45-80 μm SS particles presented completely opposite results. Both of these effects were more apparent as the steel slag replacement ratio was increased up to 30 wt. %. Concrete samples with 0-15 μm and 45-80 μm SS particles presented comparable 7- and 28-day compressive strength to the control concrete when their replacement ratios were less than 10 wt. %. Moreover, the concrete samples with 45-80 μm SS particles at 5 % dosage developed the highest compressive strengths at 7 and 28 days, which were 2 % and 5 % higher than the control sample, respectively. The pore structure results indicated that a composition of 5 % 45-80 μm SS particles was advantageous for refining the pore structures of cement paste, further contributing to the 28-day compressive strength development of concrete.