Role of fly ash, limestone powder, and calcined clay in strength improvement and hydration reactions of magnesium phosphate cement

Multiscale investigations were conducted to explore the hydration phases development of magnesium phosphate cement (MPC) incorporating supplementary cementitious materials (SCMs) such as pulverized fuel ash (PFA), limestone powder (LS), and calcined clay (CC). Strength, reaction products, chemical structures of hydration phases, and microstructures were analyzed using advanced material characterization techniques, including QXRD, SEM, TGA, FTIR, BSE-EDS, micro-Raman spectroscopy, NMR, and nanoindentation. The primary MPC hydration product, struvite, along with secondary reaction products, such as M-S-H, C-S-H, and C-A-S-H were identified to understand the development of calcium silicate and aluminosilicate phases in the MPC pastes blended with three SCMs. Moreover, MPC specimens containing 25% SCMs combining PFA, LS, and CC exhibited the 19.6% higher compressive strength at 28d as compared to the samples having only 10% PFA. Adding the SCMs into the MPC mixes led to the refined microstructures through the formation of intermediate and amorphous phases.