Influence of Biomass Bottom Ash and Tannic Acid on Properties of Magnesium Oxychloride Cement

Abstract

In order to improve the utilization rate of solid waste and solve the problem of poor water resistance of magnesium oxychloride cement, magnesium oxychloride cement with high water resistance was prepared by using biomass bottom ash as a reinforcement material and tannic acid as an additive. The hydration heat release, mechanical strength, water resistance and microstructure of the composites were analysed to determine the water resistance mechanism. It was found that adding biomass bottom ash and tannic acid changed the hydration process of MOC. Biomass bottom ash reduced the total amount and rate of hydration heat, while tannic acid prolonged the hydration heat release process. Moderate tannic acid (< 0.4%) can enhance the early compressive strength of MOC, but excessive tannic acid will lead to a decrease in strength due to the internal crystallization stress. A moderate amount of biomass bottom ash (≤20%) can improve the compressive strength, and an excessive amount will cause the strength to be reduced due to the reduction of hydration products. The softening coefficient of pure MOC after 28 days of immersion is 0.08, and that of MOC with 0.4% tannic acid and 30% biomass bottom ash is 0.93. The biomass bottom ash and tannic acid, either alone or together, significantly improve the water resistance of MOC. XRD and TG - DTG analysis showed that the addition of the two substances did not significantly change the hydration product and phase composition but affected the stability and content of phase 5. Tannic acid promotes the gelation of phase 5, and the biomass bottom ash optimizes the particle gradation and microstructure. The synergy between the two effectively enhances the water resistance of MOC.

Keywords: Magnesium oxychloride cement, Biomass bottom ash, Tannin acid, Water Resistance, Hydration heat.