ATTACK OF CEMENTITIOUS MATERIALS BY ORGANIC ACIDS IN AGRICULTURAL AND AGROFOOD EFFLUENTS - A REVIEW

摘要

This review paper concerns the attack of cementitious materials by the various organic acids found in agricultural and agrofood waste waters, among which are liquid manure, silage juice, whey, white waters, molasses... These effluents, whose pH can reach very low values, induce a severe chemical attack on concrete in farm and agrofood plant structures. They contain carboxylic acids such as acetic and propionic acids (volatile fatty acids), lactic, citric and oxalic acids and also microorganisms. The effect of bacteria is not considered. The paper first looks at the biochemical composition and pH of the medium. Then it reviews the chemical data governing the reactions between the acids and the cement paste. Afterwards, the chemical, physical and mineralogical mechanisms of attack by these acids are explored and compared to those of strong acids such as nitric and hydrochloric acids. The literature data on the kinetics of degradation are also presented and the rates of degradation are compared to those of strong acids.