Effect of Nano-Micro Waste Granite Stone Powder–Modified Superabsorbent Polymer on the Performance of Cement-Based Composites

The application of superabsorbent polymer (SAP) as an internal curing agent in cement-based materials is often limited by its adverse effects on mechanical properties. This study presents a novel SAP modified with nano-micro granite stone powder (SAP-NmGS) to address this issue. The SAP herein is an acrylic-acrylamide copolymer. During its polymerization, NmGS particles induce spatial steric hindrance, retarding the reaction to enhance the structural stability of the SAP and water retention. Additionally, the appropriate amount of NmGS particles act as physical cross-linking points, refining the three-dimensional (3D) network of the SAP. These synergistic effects result in a 430% increase in water absorption of the modified SAP-NmGS compared with unmodified SAP at a 3% NmGS content. The enhanced absorption capacity enables a reduction in the SAP-NmGS dosage in cement mortar while maintaining the same internal curing water supply. When SAP-3%NmGS was incorporated at 0.065% by cement mass, its performance was evaluated through compressive strength tests, autogenous shrinkage tests, and restrained ring cracking tests. Results indicated that, compared with the plain cement group, the 28-day compressive strength loss was limited to less than 5%, autogenous shrinkage is reduced by up to 33.5%, and restrained cracking time was delayed by 85%. NmGS modification enhanced the performance of SAP in cement-based materials, reducing adverse effects on strength while improving shrinkage resistance, crack inhibition, and durability. These findings offer new strategies for SAP application in cementitious systems.