Efficiency of natural pozzolan and natural perlite in controlling the alkali-silica reaction of cementitious materials

Pozzolanic materials have generally been found to be useful in reducing the effects of alkali-silica reaction (ASR) in cementitious composites by reacting with hydroxyl ions and portlandite to produce new phases that trap alkali ions. The main objective of this study is to compare the effects of the same fineness natural pozzolan (PZ) and natural perlite (PR) on the physical, mechanical, and microstructural changes of mortars exposed to the risk of ASR. In addition, the experimental work aims to consider the relationship between the chemical compositions of these two locally available pozzolans and their ASR attenuation levels in cementitious materials. In this context, mortar mixes were prepared using Portland cement (PC) substituted at 0%, 10%, and 20% of PZ or PR and tested after immersion in alkaline sodium hydroxide (NaOH) solution based on ASTM C1567 recommendations. Changes in mortar length and mass, ultrasonic pulse velocity, flexural and compressive strengths, X-ray diffraction, and scanning electron microscopy were considered. The results demonstrated that PR was more effective than PZ in improving the resistance of cementitious composites against ASR. The ultrasonic pulse velocity and flexural strength test results are in good agreement with the ASR expansion of all mortar mixes. Interestingly, at the same fineness, the pozzolanic activity level, silica content, and calcium/silica ratio of natural pozzolans were confirmed as accurate parameters in estimating their effects on the ASR reductions of mortars.