Effect of hydrophobic materials on alkali-silica reaction-induced deterioration of mortar: A comparative study.

The deterioration of mortar or concrete caused by the alkali-silica reaction (ASR) significantly depends on its susceptibility to moisture imbibition and exposure. This study investigated how applying hydrophobic materials in cement mortar prevents ASR-induced deterioration. Three hydrophobic materials were used, including a hexamethyldisilazane (HMDS) treated fumed-silica, a silane-based emulsion, and a silane-based cream. These hydrophobic materials were applied by directly coating the aggregates before mortar preparation or added directly to the mixture as admixtures. The effect of the applied hydrophobic materials on mortar properties was evaluated based on compressive strength, dynamic modulus, water absorption, and linear expansion. Furthermore, the microstructure and ionic distribution of alkalis from the aggregates interface were appraised using scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDS) tests. The results were compared to a mortar with no admixtures and a mortar with 20% cement replaced by fly ash (a traditional method of ASR mitigation). Coating aggregates with hydrophobic fumed silica were more effective at reducing ASR-induced expansion than directly integrating the hydrophobic materials, although at a lower degree than fly ash. • Hydrophobic materials were incorporated in mortars through two methods: aggregate coating and direct using as admixtures. • ASR-induced expansion and cracking were reduced by hydrophobic aggregates. • EDS analysis via the line approach shows the impact of hydrophobic materials on the transport of alkali ions. [ABSTRACT FROM AUTHOR]