Methodology proposition for performance evaluation of crystalline admixtures in portland cement concrete

Abstract

Permeability reducing admixtures (crystalline admixtures) have been widely used to prevent water percolation through concrete structures and in addition providing self-healing properties to the concrete, and even though these admixtures are already used in several jobs around the world, there is still no established methodology for its evaluation and characterization. Several techniques to evaluate the water permeability reduction and self-healing properties of concrete have been tested and used, but still with limited use. The purpose of this study is to propose a simple methodology that can be easily used to compare and evaluate the performance of crystalline admixtures in terms of reducing concrete permeability and its ability to seal cracks. The standard test of pressurized water penetration in concrete (ABNT NBR 10787:2011) has proven effective to evaluate the effectiveness of these admixtures regarding the water percolation through the concrete. And to evaluate the reduction of water flux through the concrete, pre-cracked specimens, at 56 days, were submitted to a constant water flow to simulate a structure exposed to a wet environment. In this study, five concrete mixes with a w/c ratio of 0.65 were evaluated, one as a reference and the others mixes with crystalline admixtures from different manufacturers. Every week, the water flux through the specimens was measured to check its decrease. The mixes with crystalline admixtures presented a significant water flux reduction after four weeks, while the reference concrete continued to show water percolation after nine weeks.