Detailed investigation of ACR in concrete with silica-free dolomite aggregate

The progress of the alkali-carbonate reaction (ACR) in NaOH or an aqueous environment at elevated temperature (60 degrees C) was investigated in concrete prepared with silica-free dolomite aggregate. The results obtained show that chemical reactions characteristic for the ACR progressed in all aged concrete systems. In NaOH aged samples, dolomite grains smaller than 2 mm in diameter went through a complete dedolomitisation process. Additionally, new Mg-Al, Mg-Si and Mg-Al-Si phases were recognized at the aggregate-cement paste interface. The less alkaline environment in the case of H2O-aged samples resulted in substantially decelerated ACR reaction. Based on observed long-term microstructural and phase changes, a detailed scheme of the ACR in concretes with silica-free dolomite aggregates was proposed. It turned out that the soluble Si-source does not necessarily originate from the aggregate itself but rather through the Pozzolanic reaction of cement binder decomposition/regeneration cycle. (C) 2019 The Authors. Published by Elsevier Ltd.