Testing For Potential Alkali Reactivity Of Aggregates And Study On The Method For Inhibiting Alkali- Aggregate Reaction

Alkali aggregate reaction (AAR) is one of the factors that affect the concretedurability most. It is impossible to estimate how much losses caused by this reaction in theworld. Many theoreticians and engineers concern it. In this paper, the alkali reactivity ofaggregates used in Tangshan and new methods for inhabiting AAR were investigated.The alkali reactivity of three typical aggregates were determined by different testmethods including petrographic examination, ultra-accelerated mortar-bar test, concretemicrobar test, concrete prism test combined with chemical analysis, XRD and SEM. Theresults indicated that the aggregates in this experiment are all argillaceous carbonate rockscontained alkali reactive minerals such as chalcedony and dolomite. The type and degreeof Alkali reactivity varied with the aggregates. In these aggregates, some are alkali silicareactivity dominated, some are alkali carbonate reactive and others have both reactivity.The inhabiting methods for AAR were investigated based on the aggregate that hasthe highest alkali reactivity with ASTM C1260 test. Several inorganic or organic additivessuch as calcium nitrate, barium nitrate, aluminum nitrate and cationic surfactant were used.Two additives were found that could inhabit alkali-silica reaction effectively. Theexpansion can be reduced by aluminum nitrate from 0.237% to 0.043%, and by cationicsurfactant from 0.26% to 0.034%.The action mechanism of the addictives was discussed from the content of availablealkali and the products. The gel products were consolidated and could absorb more alkaliafter aluminum nitrate added. It suggested that aluminum nitrate reduce expansion becauseit alters the morphology and composition of the products. The cationic surfactant addedcan decrease the amount of the products. Cationic surfactant could be adsorbed byelectronegative active silica and keep alkali from the surface of aggregates, that is, cationicsurfactant reduce expansion because it can control the process of alkali silica reaction.