Discussão sobre a caracterização da reatividade de agregados graúdo utilizados na fabricação de concretos.

Abstract

The alkali-aggregate reaction (AAR) is a deleterious chemical reaction that involves sodium and potassium ions, mainly from Portland cement, some mineral phases that may be present in large aggregates or small amounts that in the presence of water can cause expansions in concrete structures. Knowing the mineralogy of the aggregate is fundamental, because avoiding the use of reactive aggregate prevents the appearance of this pathological manifestation. The objective of this work is to make a comparison between the different test methodologies for determining the expansion of concrete prisms by the accelerated method, Brazilian standard NBR 15577- 7:2018 with RILEM AAR-4.1:2016 and modified AASHTO T 380:2018. The methodologies proposed by NBR and RILEM are very similar, differing only in the amount of aggregates and cement consumption. The method proposed by AASHTO differs in the packaging and time of the test. As the intention of this research is to evaluate the conditions of the test environment the same mold size was maintained for all evaluated methodologies. For the execution of all tests it was used a reactive large aggregate and innocuous small aggregate. The specimens tested by the NBR and RILEM methods pointed out that the large aggregate used is reactive at first reading, where the dimensional variation of the prisms was greater than 0.03%, the limit proposed by both standards. The prisms behaved in relation to the very similar expansion. The methodologies proposed by NBR and RILEM last 20 weeks, with an interval of 5 weeks for each reading. Analyzing the results found in the test that was obtained with the packaging environment as proposed by AASHTO T380: 2018 it is possible to conclude that the speed of occurrence of the expansion is greater than in the other methodologies. This is because the test conditions are very aggressive. This lasts for 56 days, readings are taken with small intervals between ages. After conducting the proposed tests and analyzing the data found, it is possible to verify that all the studied standards fulfill the main objective of characterizing the aggregate in terms of alkali silica reactivity.