The impact of carboxylic acid type hydrophobic agent on compressive strength of cementitious materials

Abstract One of the most effective methods to improve durability of cementious materials is resist the intrusion of water born aggressives by mixing with hydrophobic agent, limiting the development of compressive strength. In this study, effect of carboxylic acid ammonium salt hydrophobic agent on compressive strength of cementitious materials is examined and its mechanism is analyzed. It is investigated that the impact of hydrophobic agent on hydration degree, amount and structure of hydration products shows that hydrophobic agent has little influence on hydration and products. In contrast, the generation of calcium carboxylate and increase of air content will cause loose of the microstructure of cement pastes confirmed by electrical conductivity and zeta potential. The secondary stress is proposed to analyze the effect of microstructure change on the compressive strength. The result of this study shows that hydrophobic agent might have great sense to improve durability of concrete and the compressive strength reduction should be considered.