Mechanism study on the effect of diammonium hydrogen phosphate on the setting time and micro-nanostructure of ordinary Portland cement paste

Abstract

The effect of diammonium hydrogen phosphate (DAP) on the setting time, mechanical properties and micro-nanostructure of cement paste is investigated. The results show that with an increase in DAP content, the peak value of hydration heat of cement is delayed, but the 3d cumulative hydration heat release of the cement is basically the same. The 3d compressive strength of cement paste is not significantly different, and the 28d compressive strength increases first and then decreases. When the DAP content is 0.5 wt%, the compressive strength of cement paste is most significantly improved, increasing by 38.5%. Meanwhile, the initial and final setting times of cement paste are extended by 74.0% and 73.2%, respectively. When the DAP content is 1.0 wt%, the cement paste has the longest setting time, with the initial and final setting times extended by 101.8% and 103.5%, respectively. However, the compressive strength of the cement paste can still be improved by 10.5%. It is mainly due to the change of pH value and calcium ion concentration of cement pore solution with different DAP content, which changes the micro-nanoscale morphology of C-S-H gel, Hamaker constant between globules, microscopic Young's modulus, and pore structure.