Presentation

The degradation of concrete by internal expansive reactions is recently new in Portugal with an increasing number of the affected concrete structures over the last few years. This pathology affects several types of concrete structures, some of them of great national strategic importance, including dams, bridges and viaducts. Duarte Pacheco viaduct and the dams of Alto- Ceira, Santa-Luzia, Pracana, Fratel and Fagilde are examples of Portuguese structures affected by these expansive reactions, and some were recently repaired with enormous economic costs. When these reactions occur, which include the alkali-silica reaction (ASR) and the internal sulphate reaction (DEF), their effects are particularly dangerous because they are related with the formation of expansive products that cause the cracking of the concrete, contributing for a large reduction in the lifetime of the structure and ultimately forcing its demolition. Associated to this situation, is the fact that still does not exist an efficient and economic method to fight this form of degradation. To guarantee the lifetime of new concrete constructions we are obliged to adopt measures for the prevention or minimization of its effects in the future concrete structures.

One of the prevention methods for the occurrence of internal expansive reactions is the reduction of the alkalinity of the concrete interstitial solution. Recently, it has been used mineral admixtures, composed by natural mineral products (natural pozzolans) and industrial by-products with pozzolanic characteristics including fly ash, granulated blast furnace slag, silica fume and metakaolin, that have shown promising results in the mitigation of these reactions.

The EXREACT Project is intended to evaluate the effectiveness of natural and artificial products of national origin in the mitigation of the concrete internal expansive reactions, with particular emphasis in the study of the inhibiting mechanism of these reactions. Recently the project team has been involved in the evaluation of the effect of fly ash and metakaolin in the ASR inhibition, resulting in a PhD thesis. The developments of this project will broad the focus of the previous research into the application of new materials and into the internal sulphate reaction.

The proposed study will include the formulation of concrete mixes incorporating these materials and the performance evaluation studies in accelerated and natural exposition conditions. This Project will also allow the improvement of methodologies for the diagnosis and prognosis of the occurrence of internal expansive reactions in the existing concrete structures in Portugal.