Effects of different alkaline solutions on the expansivity of rock prisms of an alkali-reactive dolostone from Valcheta (Río Negro, Argentina)

A fine-grained argillaceous reactive dolostone was identified in Argentina. In alkaline conditions, a clear dedolomitization reaction occurred, accompanied by a deleterious expansive process. The purpose of this paper is to investigate the correlation between the rock prism expansion and the reaction progress. Rock expansion (in high and low porosity samples) was evaluated by a modified ASTM C586 test method, using NaOH, KOH, LiOH, and Ca(OH)2 solutions. The reactivity was verified in concrete mixtures applying a method similar to ASTM C1293, using the dolostone as coarse aggregate. To evaluate the reaction progress during the tests, mineralogical changes in the rock were quantified using XRD (Rietveld). In addition, the mercury porosimetry test was performed to investigate the changes in the rock pore structure. Finally, chemical analyses of the contact solutions (CO32−, OH−, Na+, K+, Li+) were done. Considering the results obtained, some controversial aspects of the theories proposed in the literature are analyzed. •Rock expansion (ASTM C586) begins with the appearance of CO32– in the test solution•Incubation and principal-expansion periods are related to the alkali cation radius•Eventual depletion of dolomite or OH– does not explain the low rock expansion rate•Dedolomitization is a necessary but not sufficient condition for rock expansion•Despite low expansion recorded, the advance of LiOH attack on the rock is very fast