Mechanical properties and microstructure of ultra-high performance cement-based composite incorporating RHA

The effects of the addition of rice husk ash (RHA) on the mechanical and microstructural properties of an ultra-high performance cement-based composite (UHPCC) was studied. The microstructure of the UHPCC was investigated using X-ray diffraction, mercury intrusion porosimetry, scanning electron microscopy and other analytical test methods. The results showed that the mechanical performance was improved with the addition of RHA. Mortars blended with 15% RHA showed the highest compressive and flexural strengths. For mortars reinforced with 3% steel fibres by volume, both flexural and compressive strengths were remarkably enhanced. The optimal content of RHA was found to be about 10–15%. The addition of RHA decreased the hydration heat evolution rate of the cementitious composites, but the hydration process was brought forward due to the addition of RHA. As a result of calcium hydroxide consumption through the pozzolanic reaction of the RHA, the interface was strengthened with an increase in curing time and the microstructure of the mortar containing RHA blended was denser than that of mortar without RHA. The high pozzolanic reaction and the filler effect of RHA contributed to a finer pore structure and a decrease in porosity.