Microstructural analysis and durability performance of concrete incorporating calcium-carbonate-rich marble waste as fine aggregate replacement

Abstract Calcium-carbonate rich (CCR) marble waste with high calcium-carbonate content was investigated as a possible full or partial substitute for natural fine aggregate in concrete. Its effect on durability performance and microstructural development was studied in this research. Concrete mixtures with 0%–100% CCR replacement were prepared at a constant water–cement ratio to test their workability, mechanical strength, sorptivity, drying shrinkage and microstructural characteristics. The findings revealed a gradual decrease in workability with the increasing CCR content, while maximum slump reduction occurred at full replacement. There was a notable enhancement in mechanical performance at moderate replacement levels (45%–60% CCR incorporation)—compressive strength of CCR concrete increased from 33.0 MPa to 45.7 MPa along with improvements of split tensile and flexural strengths. The improved packing of particles and refinement of pores reduced the sorptivity and long-term drying shrinkage, indicating improved moisture resistance and dimensional stability. The x-ray diffraction and scanning electron microscopy analyses confirmed that the intermediate contents of CCR caused matrix densification as well as a refined pore structure. However, replacement levels above 60% caused slight performance deterioration due to disruption of the aggregate skeleton, increased localized porosity, and reduced matrix uniformity. Overall, replacement of natural sand by 45%–60% CCR marble waste gives the best balance between mechanical performance and durability enhancement along with the efficient utilization of marble waste in concrete.