Research On Alkali-silica Reaction In Alkali-activated Slag

Alkali-Aggregate Reaction (AAR) is a process of producing water-swellingproperties by the reaction involving the active ingredient of aggregates and the poresolution of the alkali (Na2O+K2O) under the appropriate humidity. The alkali andcalcium ion both play an important role in the reaction procedure. Compared with thetraditional Portland cement-based materials, alkali-activated slag (AAS) contains ahigher concentration of alkali, which arouses great attention on the research of theAAR of AAS. The absence of calcium hydroxide in the hydration products of thesystem can lead to lower calcium content in the pastes pore solution of AAS. However,the conclusions of relevant researches of AAR in AAS are so fewer, even exist somecontradictions. What’s more, the artificial aggregate or the high alkali reactivity opalsare usually used in the previous studies, but the AAR researchesof low alkali activityof natural aggregate in alkali-activated slag are fewer. In addition, the applicability ofexperimental methods is also questioned by researchers.The paper is referring to the Accelerated Mortar Bar (ASTM C1260). In the first,the alkali reactivity of sand and pebble of the Xiangjiang River in Hunan Wangchengis tested, and the alkali-silica reaction is determined by means of the scanningelectron microscopy and energy spectrum analysis. Secondly, the alkali-silica reactionof alkali-activated slag containing the reactived aggregates is investigated in detail. Inthe last, the alkali-silica reaction in alkali-activated slag and Portland cement arecompared by means of three kinds of different curing mechanisms.The results show that the sand has the potential alkali reactivity and the pebblehas the high alkali activity from Xiangjiang Wangcheng city. And the alkali activatedslag occurs alkali silica reaction containing those aggregates, even the destructivedexpansion, which is affected by the activator types, attributes and alkali dosage. Theaddition of fly ash can inhibit the alkali-silica reaction expansion in sodium silicateslag mortar, but the effect has a relationship with fly ash replacement content. Andthere is an optimal replacemen.When immersed in NaOH solution, the expansion of the sodium silicate slagmortar is bigger than Portland cement mortar’s in earlier age, but the rules instead inthe later stage. In steam curing and deionized water immersion, the expansion ofwater glass slag mortars is higher than Portland cement mortars’ under the sameconditions. And the pore solution of the mortars is an important influence factor on expansion. What’s more, the accelerated Mortar Bar method can also be applied toalkali-silica reaction researches of alkali-activated slag, but the comprehensive andaccurate determination still need to be further studied.The studies of the paper detected the presence of alkali activity of sand andpebbles in Wangcheng City of Xiangjiang River. On this basis, the alkali silicareaction of alkali-activated slag containing these two aggregates is researched indetail, and the inhibition effect and mechanism of the fly ash on the alkali-silicareaction is also explored, which can offer information for the mixture design of thealkali activated slag. What’s more, comparing the alkali silica reaction inalkali-activated slag with it in Portland cement is advantageous to deepenunderstanding of alkali silica reaction of former.