Attack of cement pastes exposed to organic acids in manure
Résumé
Manure such as silage effluents and liquid manure contains organic acids which constitute a severe chemical threat toward the concrete of agricultural structures. The purposes of this study were to identify the chemical composition parameters that influence durability by analysing the behaviour of the chemical elements of the cement paste (Ca, Si, Al, Fe and Mg) in organic acid solutions and to compare the intensity of the chemical attack by the different acids found in liquid manure. This study was carried out on cement pastes made from four binders (ordinary Portland cement, slag cement, OPC blended with silica fume and OPC blended with fly ash). The hardened cement pastes were first crushed, then immersed in solutions made of five organic acids with an initial pH of 4 and constantly stirred. The pH and the concentrations of major elements were monitored over time.
The results show that Si, Al, and Fe appear to be favourable elements for the chemical resistance of binders whereas the amount of Ca should be limited. Moreover, it is shown that the four acids found in liquid manure (acetic, propionic, butyric, iso-butyric) are equally aggressive. Lactic acid, present with acetic acid in silage effluent, is more aggressive according to the value of its pKa.