Estudo do comportamento reológico no tempo de argamassas com substituição de sílica de casca de arroz

Abstract

In this research, the properties and characteristics of mortar in fresh state were evaluated at different time intervals and at different test speeds, with substitutions of Portland cement with rice husk silica (SCA). The analysis was done from a reference trace where mass substitutions of Portland cement by SCA were made in 5, 10, 15, 20 and 30%, with the water/cement ratio fixed at 0.71. For the analysis of the rheological behavior of the mortars, the tests of consistency table (Flow Table), density of the mass and air content incorporated soon after the production of the mixture, and the modified Vicat and Squeeze Flow in the ages of 15, 60, 120 and 180 minutes. The Squeeze Flow test was also performed for different speeds (1mm/min, 0,1mm/s and 1mm/s). The results obtained by the consistency tests (Flow Table and modified Vicat) decreased as the percentage of ACS was increased. With advancing age, the results in the modified Vicat assay showed that the penetration of the cone decreases, because the silica absorbs the water of the mixture, leaving it dry. For the physical assays of mass density and the incorporated air content, the results did not present significant alterations with inclusion of ACS. In the Squeeze Flow test the data suggest an improvement in the workability of the mortar with a 5% substitution in the mixture in relation to the reference trait, but this behavior does not repeat in later ages. Further, it can be seen that the displacement decreased and the stiffness increased. The flow stress of the mixtures and the viscosity will vary according to the test speed. Higher velocities, such as the 1mm/s test, are not feasible for analyzing the Squeeze Flow data, because the elastic behavior of the mortar is very small. The values of maximum traction increased with the advancement of age and the higher the percentage of silica present in the mixture.