Effect of montmorillonite as additive on the properties of cement-based composites

Abstract The aim of this study was to investigate the effect of montmorillonite as additive on the properties of cement paste and mortar. Montmorillonite was used at 0%, 5%, 10% and 15% additive by weight of cement, and the water/cement ratios of 0.45 and 0.55 are considered for the cement pastes and cement mortars with the sand/cement ratio of 1, respectively. Experimental results indicate that the use of montmorillonite as cement additives increases the compressive strength except the specimens containing 15% montmorillonite at the age of 28 days. The water absorption and initial surface absorption decreased with the increase of montmorillonite additives for the cement pastes. However, the cement mortars had an opposite test result in water absorption and initial surface absorption. The cement pastes and mortars containing montmorillonite have higher adsorption-desorption values than those of the plain cement pastes and mortars. Meanwhile, scanning electron microscopy and mercury intrusion porosimetry tests indicate that the cement paste containing montmorillonite are denser than that of the plain cement paste. X-ray diffraction analysis showed that the main hydration products are portlandite, hatrurite and calcite in cement paste and quartz and portlandite in cement mortar.