Effect of AH3-PCE Ultrafine Composites on the Properties of Sulfoaluminate Cement-Based Materials

The use of superfine particles has been found to be a promising method for accelerating cement hydration. Amorphous aluminum hydroxide (AH3) is a key hydration product in sulfoaluminate cements and our preliminary research work indicated that the ultrafine amorphous AH3 accelerates the hydration rate of sulfoaluminate cement-based grouting materials (SAGMs). However, the ultrafine AH3 tends to agglomerate easily, which affects its effectiveness. In this study, aluminum hydroxide-polycarboxylic acid superplasticizer (AH3-PCE) ultrafine composites were prepared using the sol–gel method, and their effect on the hydration and hardening process of SAGMs was investigated. The results showed that the particle size of the AH3-PCE ultrafine composites decreased and then increased with increasing amount of PCE and there was a strong interaction of AH3 with PCE through the oxygen atoms of C–O–C. AH3-PCE ultrafine composites provided nucleation for the growth of bayerite and ettringite (AFt). Moreover, the AH3-PCE ultrafine composites released aluminum ions and PCE in an alkaline solution at pH 12.5. The AH3-PCE ultrafine composites promoted cement hydration, adjusted the pore structure of the hardened paste, and improved the compressive strength at all ages owing to the synergistic effect of nucleation, aluminum ions, and PCE released from the AH3-PCE ultrafine composite.