Effect of rice husk ash on early hydration behavior of magnesium phosphate cement

Abstract

The application of rice husk ash (RHA) on magnesium phosphate cement (MPC) can increase the rational utilization of resources and improve the properties of MPC. RHA with the characteristics of porous and high activity as admixture has a certain influence on the hydration behavior of MPC. In this research, rice husk is calcined and ground reasonably to improve the activity of RHA. The particle size distribution, structure and micromorphology of RHA were characterized via laser particle size analyzer, X-ray diffractometer (XRD) and scanning electron microscope (SEM). The effects of RHA on hydration behavior, setting time and early compressive strength (3 h, 1 d, 7 d) of MPC were researched. Results indicated that the setting time was shortened about 2 min with the addition of 7% RHA. The compressive strength of RHA/MPC composites increased by 39.2%, 39.7% and 25.7% incorporating with 5% RHA at the age of 3 h, 1 d and 7 d. The hydration heat analysis (TAM Air) showed that RHA postpone the early hydration of MPC and cause a second exothermic peak. The XRD and thermal gravity analysis (TG/DTG) suggested the number of hydration products is increased with the introduction of RHA. The porosity level of RHA/MPC composites was dropped through the mercury intrusion porosimetry (MIP). RHA plays a positive role in providing the site of hydration reaction and an alkaline environment for the RHA/MPC composites. It can be known that the compactness of RHA/MPC composites was promoted through SEM observation.