Research on the Macromechanical Properties and Microstructure of Carbonized Steel Slag Fine Aggregate Concrete

Abstract

To investigate the macromechanical properties and microstructural characteristics of carbonated steel slag fine aggregate concrete (CSSFC), steel slag with particle sizes < 5 mm was selected. After carbonation, the steel slag was used to replace natural sand in equal volumes, resulting in concrete samples with carbonated steel slag fine aggregate (CSSA) contents of 0%, 10%, 20%, and 30%. The study evaluated the compressive strength, splitting tensile strength, flexural strength, and axial compressive strength of CSSFC. Additionally, stress-strain curves for the concrete were obtained. The microstructural characteristics of CSSFC were analyzed using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), nanoindentation, and mercury intrusion porosimetry. Furthermore, the fractal characteristics of the pore structure in CSSFC were analyzed. The results indicate that as the content of CSSA increases from 0% to 30%, the compressive strength, splitting tensile strength, and axial compressive strength of the CSSA concrete progressively improve. CSSA demonstrates significant hydration activity, which enhances the densification of the interface transition zone (ITZ) between the cement matrix and the steel slag aggregate, thereby reducing microcracks. Compared to natural aggregates, CSSA shows a more pronounced interface transition zone, with an approximate width of 8 μm. The average hardness and elastic modulus of CSSA are 78.3% and 87.7% higher than those of natural aggregates, respectively. As CSSA content increases from 0% to 30%, porosity initially increases and then decreases. Additionally, as the fractal dimension rises, the average pore diameter, median pore diameter, compressive strength, splitting tensile strength, and flexural strength increase, while the pore surface area decreases.