Use of Nevada\u2019s Natural Pozzolans to Mitigate Alkali-Silica Reactivity

2019Final Report, June 1, 2017- December 30, 2018PDFTech Report224-14-803 TO 16GR04162Alkali silica reactionsPortland pozzolan cementPozzolanPozzolanic actionfly ashexpansionstrengthUnited StatesNevadaNevada. Dept. of TransportationGhafoori, NaderKian, ArashUniversity of Nevada, Las VegasUniversity of Nevada, Reno. Center for Advanced Transportation Education and ResearchNevada. Department of TransportationUS Transportation CollectionThe aim of this study was (i) to assess the extent of reactivity of the aggregates, quarried from seven different sources, suspected of being conducive to ASR, and (ii) to compare the effectiveness of industrial (Class F fly ash) and natural pozzolans in mitigation of alkali-silica reactivity of the studied aggregates. To this end, seven aggregate sources, four natural pozzolan sources, and one source of Class F fly ash were used. ASTM Type V Portland cement was replaced at four levels of 15, 20, 25, and 30% by different pozzolan types and sources. A uniform water-to-cementitious materials ratio of 0.47 was used. Beam shaped mortars were tested for ASR-induced expansion for eight weeks. In addition, companion mortar cubes cured for 90 days in a salt-water environment and in a controlled moisture room were tested in compression. The findings of this investigation revealed that the ASR mitigation of the studied aggregates depended on the aggregate source, natural pozzolan source and content, and immersion age. For nearly all natural and industrial pozzolans used in this study, 15% by weight of Portland cement was sufficient to mitigate alkali-silica reactivity of the studied reactive aggregates. The loss in strength of the studied mortars also depended on aggregate and natural pozzolan types and sources, and reduced with increases in Portland cement substitution level. Overall, the four natural pozzolan sources used in this study exhibited similar to better performance, in comparison to that of the Class F Fly ash, in suppressing the alkali-silica reactivity of the reactive aggregates.79