Concrete Repair, Rehabilitation and Retrofitting II – Alexander et al (eds) © 2009 Taylor & Francis Group, London, ISBN 978-0-415-46850-3 241 Surface protections to prevent Alkali-Aggregate Reactions (AAR) in concrete structures L.F.M. Sanchez University of São Paulo, São Paulo, Brazil S.C. Kuperman University of São Paulo and DESEK, São Paulo, Brazil P.R.L. Helene University of São Paulo, São Paulo, Brazil ABSTRACT: It is very difficult and expensive to repair or rehabilitate concrete structures suffering from AAR, and for these cases, a preventive solution is desirable, both technically and economically. However, when a reactive aggregate is used to produce a concrete and its deleterious effects are discovered after its placement, some care should be taken. Until now, there is no consensus on how to repair structures suffering from AAR; however, several types of repairs as surface protection can be used. Some researchers have been trying to study surface protections to inhibit the surface moisture and the water entrance. Their thought is that the expansion due to AAR can eventually be stopped and the concrete structure can cohexist with this problem without serious effects. Some materials have already been tested as epoxi, latex and acrilic coatings. In addition, some repellents coatings were tested too. This work studies four differents types of coatings that can be used in concrete structures with the attempt to discover if the type of coating is effective or not to prevent AAR. The types of materiais used were a silicone coating, an epoxi coating, a cimentitious coating modified with latex and a flexible poliuretane coating. To perform this study, the Accelerated Concrete Prism Test (ACPT) was carried out. This test method can classify an aggregate as innocuous or reactive in 3 months for ordinary concrete and 6 months for concrete with admixtures. Four reactive aggregates were used in this research (two granites—from São Paulo and Recife, one granite/gneiss—from Recife and one quartzite from São Paulo). The results showed that silicone coating and cimentitious coating modified with latex have a great potential to be used as surface protection against AAR. However, flexible polyurethane has not shown good behavior. 1 INTRODUCTION The alkali-aggregate reaction (AAR) is a chemical reaction between some siliceous or carbonate aggre- gates and the alkalis that are provided from cement. This chemical reaction produces an alkaline gel that when absorbing water expands and cause deleterious effects to concrete structures. In Brazil and in the world, precautions have been made to avoid AAR. It is known that the best way to avoid AAR is the prevention. There are many tests methods that can classify an aggregate according to its potential reactivity. Among them, the acceler- ated concrete prism test (ACPT) is a test method that can classify an aggregate as reactive or innocu- ous at 3 months. Even though this test has not been normalized yet, it has been showing promising results. However, there are some structures that are suffer- ing from AAR and need to maintain their intended function. For these structures, surface protections can be used with the intention of stopping or decreasing the expansion caused within the concrete. These surface protections work inhibiting the water ingress and then decreasing the rate of expansion of a concrete element. If the concrete element does not have any structural problem, a good surface protec- tion can control the problems caused by AAR. 2 ACCELERATED CONCRETE PRISM TEST (ACPT) In the beginning of the 90’s, Ranc and Debray pro- posed an accelerated test method that could in less than 8 months, identify and classify the reactivity of some