Empirical Study of Aggregate Alkali-Silica Reactivity in Concrete Using Nigerian Quarry Aggregates

Alkali-silica reaction in concrete can cause expansive cracking, structural deterioration, and premature infrastructure failure, yet systematic empirical assessment of the ASR potential of aggregates from Nigerian quarry sources is absent from the published literature. This study empirically assesses alkali-silica reactivity in aggregates from 15 quarry sources across South East, South West, and North Central Nigeria. Aggregate petrographic examination, ASTM C1260 accelerated mortar bar test, and ASTM C1293 concrete prism test were applied to samples from each quarry. Mineralogical characterisation was performed by X-ray diffraction to identify potentially reactive silica polymorphs. The effect of supplementary cementitious materials (fly ash, silica fume) on ASR mitigation was tested on the most reactive aggregates. Results indicate that six of fifteen quarry sources contain potentially reactive silica concentrations above 5 percent strained quartz by petrographic analysis. Accelerated mortar bar expansions exceed the ASTM C1260 rejection threshold of 0.20 percent at 14 days in four of fifteen aggregate sources. Aggregates from the Ogun State amphibolite quarry show the highest reactivity (mean expansion 0.38 percent). Silica fume addition at 10 percent cement replacement reduces expansion below harmful thresholds for all reactive aggregates. The study contributes the first systematic ASR characterisation of Nigerian quarry aggregates and recommends routine petrographic screening for all new quarry sources.

Keywords: alkali-silica reaction, aggregate reactivity, concrete durability, Nigerian quarry aggregates, empirical study