Efeito da umidade no comportamento viscoelástico de misturas argila-rocha

Abstract

Drying is one of the most critical forming steps in the ceramic tile production. Usually defects such as cracks and surface distortion are produced in this processing step. One way to minimize these defects is to reduce the amount of water used to shape the ceramic body. However this water reduction directly interferes in the forming process. This work aims to evaluate the mechanical behavior of ceramic green bodies in order to understand the interactions of clay-air-water mixtures, and how it behaves when rock powder and surfactant are added. For that, uniaxial compression and creep and relaxation tests were performed. They allowed, through the stress-strain curve, to assess the clay plastic response to the variation of moisture contents and rock powder addition. Workability curves were produced by the product of the yield stress and maximum deformation. The tests showed that the rock powder was able to reduce moisture of maximum workability of 18.0% to 13.7%. The green body packing density variation as a function of the forming moisture directly correlates with its compressive behavior, specifically with the yield stress. It turns possible to quantify the cohesion of the produced ceramic bodies. The addition of rock powder to the clay decreased the cohesion of the ceramic green body. The existence of different green body hydration/saturation states were identified namely the pendulous, funicular with open porosity, funicular with closed porosity and capillary states. Creep and relaxation tests were performed which showed that the clay body has a viscoelastic behavior, i.e. deformation is a function of time, independently of the green body water content. It was also shown that the use of surfactant can reduces the processing water consumption without affecting its mechanical behavior, because it can cause a clay with 18.3% moisture to flow in the same way that a clay with about 24.5% moisture.