Activation of alkali-silica reactivity under microwave action and passivation of reactive aggregate by treatment with lithium nitrate

摘要

The alkali-silica reaction (ASR), developed in the presence of reactive mineral aggregates, is responsible for numerous cases of cracking and consequent deterioration of concrete structures. This work presents a contribution to the development of a chemical method for the activation of the alkali-silica reactivity of an aggregate in its commercial granulometry, in a short time, through the application of microwaves and verification of lithium nitrate addition influence to mitigate the reaction. A proven reactive granite aggregate was used at different microwave application times with fixed power of 700 W, in neutral and basic media. Results on the aggregate reactivity were obtained in 5 min of microwave application, statistically equivalent to tests with 30-day immersion. It was observed that the most affected phases during the process are non-crystalline silica, and a gel-like phase similar to the alkali-silica reaction product was also obtained at the end of the tests. In addition, a pre-treatment of the aggregate was performed with 0.5 to 2% lithium nitrate additions, with and without microwaves, in neutral and basic media. It was observed that additions of at least 0.5% significantly inhibit the silica dissolution, but with 2% of this compound, it is possible to observe the formation of a coating on the aggregate's surface with lithium silicate.