Effects and mechanisms of capric acid/silica capsule on water absorption reduction of cement paste

Abstract

Inspired by the structure design on biomaterials for drug delivery, the encapsulation of hydrophobic capric acid (CA) core with a hydrophilic silica shell was proposed and demonstrated in a cement paste system for improving the resistance to water absorption. Firstly the fabrication of CA/silica capsule by interfacial polymerization reaction was reported. Subsequently, the effects of CA/silica capsule and mono-doped CA-hollow silica as hydrophobic admixtures on the compressive strength, water absorption, hydration process and pore structure of 28-day cement pastes were studied. Compared with the mono-doped one, the cement paste incorporated with the capsule exhibited an increased compressive strength and hydrophobicity with reduced water absorption. The increment in the compressive strength and the resistance to water absorption of capsule/cement paste was further ascribed to the improved dispersion and possible sustained release of CA/silica capsule in water, resulting in the improved hydration degree with refined pore structures and the hydrophobicity of the cement paste matrix. The study based on prepared capsule materials suggested a simple but effective approach to the fabrication of hydrophobic cement-based materials with reduced water absorption and extended service life.