Effect of cement composition and the storage conditions on the morphology of ASR products in concrete

Under natural conditions, the alkali silica reaction (ASR) is a slow degradation process in concrete. Therefore, accelerated laboratory test methods are used to estimate the alkali‐reactivity of aggregates and concrete performance regarding a damaging ASR. In this study, concrete cubes were stored in a fog chamber at 40 °C/100% RH and at outdoor conditions in Munich climate for up to 9 years. Opaline sandstone/flint (25 vol.%) was used as reactive aggregate. 15 wt.% of OPC was replaced by fly ash and compared with the reference mix with 100 wt.% OPC. The cracks widths of the cubes were measured regularly. To investigate the effect of accelerating test conditions on the morphology of reaction products, the concrete microstructure, pore solution composition and ARS products formed under accelerated and field conditions were investigated. The present study shows that accelerated test methods consider only partial aspects of the complex mechanisms of ASR in concretes containing pozzolanic fly ash. Storage conditions have a direct effect on the morphology of the ASR products, the porosity and the pore solution composition of the concrete. When testing blended binders under accelerating conditions, opposing mechanisms are achieved and the chemical and physical processes can be changed significantly.