Evaluation of Alkali Silica Reaction in Fly Ash Concrete Using an Accelerated Performance Test Method

The effectiveness of fly ash as a supplementary cementitious material (SCM) to inhibit damaging alkali silica reactions (ASR) in concrete has been proved in many investigations. However, a reliable evaluation of fly ash concrete with accelerated test methods is difficult and problematic. To assess the susceptibility of concrete to damaging ASR various methods are currently used to accelerate the reaction, e.g. increased temperatures, storage in alkaline solutions. However, these conditions accelerate the pozzolanic reaction of fly ash as well. Thus the use of a 60 °C concrete prism test developed for aggregate evaluation in Portland cement concrete leads to an incorrect assessment of fly ash concrete. The present investigations focus on the variation of preliminary storage conditions duration with regard to developing a modified performance test for fly ash concrete. The effect of high temperatures on the pozzolanic reaction and thus concrete porosity and pore solution composition was investigated by mercury intrusion porosimetry and optical emission spectroscopy. The results of the modified performance test were compared with the behaviour of 10 years’ old concretes exposed outdoors. As a result, longer preliminary storage times of about 28 days at 20 °C are recommended for a reliable evaluation of the risk of a damaging alkali silica reaction in concretes containing fly ash.