Effect of Rice Husk Ash as Supplementary Cementitious Material on the Performance of Cement-Based Pastes Continuously Exposed to Organic Acid Solution (Vinasse)

Abstract

In the present study, rice husk ash (RHA) was evaluated as supplementary cementitious material in portland cement pastes subjected to acid attack from vinasse, an acid residue from ethanol production. RHA and quartz (inert) were used in amounts of 10% and 20% in cement pastes. Mass loss variation, surface roughness, degradation-front progression, compressive strength, portlandite content, and mineralogical changes of the pastes were evaluated during 3 months of continuous exposure. In general, physical and mechanical properties were seriously affected for all pastes, except for the mix containing 20% RHA. The use of RHA did not cause a considerable change in the mineralogical composition of the pastes, being quite similar to that in the reference (Ca-bearing phases). As a consequence, chemical resistance of all pastes showed similar behavior in terms of mineralogical assemblage after exposure in vinasse, according to thermogravimetric analysis (TGA) and differential thermogravimetry (DTG) results and a qualitative analysis of X-ray diffraction (XRD) results, since the aggressiveness of the attack by the weak acids present in the vinasse is strongly related to the solubility of their calcium salts.