Effect of superplasticizer admixtures on renderings mortars with cement-lime and limestone filler

from hydration kinetics to adhesion on ceramic bricks

Abstract

This study investigated the effect of different types of superplasticizers on the properties of mortars with high levels of cement replacement (> 30%) by hydrated lime and limestone filler. Three superplasticizers were evaluated: one lignosulfonate (LS) and two polycarboxylates (PCA and PCB. The superplasticizer content was determined by rotational rheometry. Tests were performed on pastes to analyze hydration kinetics; on mortars to evaluate water content, workability, and mechanical performance; and on walls to verify the applicability of the mortars on ceramic blocks, including bond strength. The type of superplasticizer is crucial for the properties and applications of mortars. The polycarboxylates promoted better dispersion of fine particles, resulting in a matrix with higher strength and lower permeability. The mortars with PCA exhibited gains of over 85% in tensile bond strength, meeting the normative requirements for applications as an external rendering (C40_PCA). The LS saturation content caused excessive retardation (> 72h) and higher air entrainment, compromising the mechanical properties of the mortars and the bond to the ceramic blocks.