Influence of mixing process on mortars rheological behavior through rotational rheometry

Mixing is one of the mortar processing steps (the others being proportioning, transport and application) that, due to its apparent operational simplicity, has been somewhat undermined. However, the mixing process quality has direct influence on the mortar's rheological behavior and its hardened state properties. In this context, this study's objective is to assess the influence of two mixing parameters (time and water addition rate) on the characteristics of the produced mortar. Both mixing and flow measurements were performed in a rotational rheometer developed at POLI/USP-Brazil. In this equipment, the mixing strain rate is given as a function of torque evolution. Mortar tensile strength, modulus of elasticity and volumetric porosity were evaluated in its hardened state. "Bad mixing" conditions can arise from too short mixing times or too slow water loading. These bad mixing conditions led to mortars with lower mechanical strength and more unfavorable rheology, meaning high thixotropy and flow curve loops with big hysteretic area. When admixture was employed, mixing resulted in a mortar with higher entrained air leading to negative effects on the mechanical properties of the hardened material. (C) 2019 Elsevier Ltd. All rights reserved.