Influência de dois tipos de metacaulim no comportamento reológico e nas propriedades físicas e mecânicas de misturas a base de cal hidratada

Abstract

Lime-based mortars are commonly used in the restoration and conservation of historical buildings due to their compatibility with centuries-old construction materials. The incorporation of pozzolanic additives enhances properties such as permeability, durability, and mechanical strength. However, the performance still falls short when compared to conventional materials like Portland cement. Moreover, there is a lack of studies focusing on the rheological behavior of lime-based mixtures. In this context, the present research aims to evaluate the performance of hydrated lime pastes and mortars modified with commercial metakaolin (MK) and calcined kaolin (CK), using different lime:pozzolan ratios. Nine mixtures were investigated for each pozzolan type, with the pozzolan content gradually increasing from 10% to 90%, in order to assess its impact on rheological properties and mechanical performance. Regarding rheology, pastes were evaluated in the fresh state through mini-slump tests and rotational rheometry, using parallel plate and concentric cylinder geometries. Mortars were tested for flow spread, fresh bulk density, squeeze-flow behavior, flexural strength, and compressive strength. Rheological tests showed that the pastes exhibited non-Newtonian behavior and were well described by the Herschel–Bulkley (HB) and Bingham (B) models. The change in rheometer geometry revealed higher shear stress values with parallel plates. Paste viscosity increased with higher pozzolan content. Both MC and CC pastes demonstrated thixotropic behavior, characterized by a hysteresis area. Mortars containing MC required more water than those with CC, while CC mortars achieved higher mechanical strengths, with maximum values of 0.98 MPa in flexural strength and 8.90 MPa in compressive strength. Squeeze-flow results indicated that CC mortars formed a stiffer initial structure, and the pozzolan content played a key role in the development of mixture stiffness, as mortars with higher metakaolin content reached greater strength in shorter time periods.