Observation of reactions between dolomite aggregate grains and lime–based binder in lime mortars

Abstract eng:
This paper investigates the process of alkali-carbonate reaction (ACR) in lime-based mortars prepared with certain dolomite aggregate. As binder either pure calcite lime putty or combination of the putty and volcanic tuff was used. The progress of ACR was studied using a petrographic microscope and scanning electron microscopy with X-ray microanalysis (SEM/EDS), on samples exposed to different conditions: accelerated conditions (1M NaOH solution at 60 °C, distilled water at 60 °C, and 1M NaOH solution at 20 °C) and reference conditions (distilled water at 20 °C). Compressive tests on mortar bars were also carried out, parallel to the microscopic investigation. The results indicate that the presence of hydroxide ions in binder is enough for the initiation and progress of ACR in the lime-based mortars with dolomite aggregate, although sodium hydroxide solution and/or increased temperature of 60 °C accelerate the reaction. Compressive strength of the pure lime mortar with dolomite aggregate, exposed to water or the NaOH solution, increases with time considerably, due to ACR, and can be attributed to alterations to the microstructure of the mortar. However, for the lime-pozzolana binder ACR seems to proceed slower than for the pure lime binder, if increase of the mortar’s compressive strength over time is taken as indicator of the reaction. Key words: Alkali aggregate reaction, pure lime binder, lime-pozzolana binder, dolomite aggregate

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