LEACHING OF CEMENT PASTES EXPOSED TO THE ACTION OF MANURE ORGANIC ACIDS: COMPARISION OF THE RELATIVE AGGRESSIVENESS OF THE DIFFERENT ACIDS

摘要

Manure, such as silage effluents and liquid manure, contains organic acids which constitute a severe chemical aggression toward the concrete of agricultural structures. The intensity of the aggression depends on several parameters such as the acid dissociation constants, the solubility products in water of the salts issued from the reaction between the cementitious matrix and the acids and the formation constants of complexes in solution. However, the knowledge of these values does not permit prediction of the relative aggressiveness of the different acids towards the cement based matrix. The purpose of this study was to compare the intensity of the chemical aggression intended by the different acids. The aim is to determine if the action of acetic acid is representative of all the manure acids; as it was assumed in many studies that simulating the attack of manure may be conducted with the use of acetic acid only. This study was led on hardened OPC pastes, first crushed, and immersed in solutions made of five organic acids with an initial pH of 4. The pH and the major elements concentrations were monitored over time. The results show that the four acids of 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.