Recycling of waste crushed stone powder for alkali-activated material production

The growing use of crushed stone and manufactured sand poses a major challenge to the recycling of their by-product known as crushed stone powder (CSP). To establish an effective recycling method for CSP, the authors conducted a detailed investigation on the setting, strength, and durability of alkali-activated materials (AAMs) with slag (GGBFS) and CSP as precursors, and examined their chemical and microstructural characteristics by X-ray diffraction (XRD) and scanning electron microscope (SEM) analysis. Experimental results clarified in detail the performance features and influencing factors of AAM made from a blend of CSP and slag, and indicated that CSP can be utilized as an inactive precursor in a large blending ratio (50–80%) to produce AAMs with high strength and excellent durability. The GGBFS/CSP-based AAMs have high flexural strength, reaching up to 1/5 ~ 1/6 of the compressive strength, surpassing 15.0 MPa. The AAMs using CSP almost retain the crystals from CSP within them, and the presence of CSP particles fragments C-A-S-H gels of polymerization reaction product, making them granular and discontinuous. Compared to the siliceous CSP, the limestone CSP slightly enhanced the strength properties of AAM.