Expansive behavior of an alkali-carbonate reactive dolostone from Argentina: Proposal of an osmotic theory-based model to explain the expansion caused by the alkali attack

Abstract

The expansion mechanism of dolomitic rocks in alkaline environments is complex and a current topic of debate, since two different chemical reactions can coexist: one linked with silica attack (alkali-silica reaction, ASR) and the other with dolomite attack (alkali-carbonate reaction, ACR). In previous works, a potentially reactive, fine-grained argillaceous dolomitic rock was identified in Argentina, with similar expansive characteristics to the typical American reactive carbonates. When this rock is used as aggregate in mortars or concretes, the dolomite experiences a clearly expansive dedolomitization reaction, which cannot be controlled by the classical techniques that allow the inhibition of ASR: supplementary cementitious materials (SCMs) (fly ash, natural pozzolan, silica fume, etc.) or Li-based admixtures. Since none of the classical theories proposed by the literature adequately describe the expansive behavior of this rock, an expansion mechanism based on the osmotic phenomenon is proposed in the present work. This mechanism describes the behavior of the Argentine dolostone more appropriately and allows explaining the effect of the main factors involved in the concrete expansion (pH of the pore solution, nature of the alkali cation associated with the OH−, role of water in the expansion, temperature, aggregate particle size, effect of the SCMs, etc.). The basis of the osmotic model is presented, and its advantages are discussed compared with the classical ACR mechanisms proposed by the literature.