Research On Alkali Reactivity Of Sand And Gravel From Xiangjian G River And Design Of Cementious Material For Preventing The Alkali-Aggregate Reaction

The alkali–aggregate reaction of concrete has always been a hot researc h allover the world. A mass of literatures have shown that the incorporation of mineraladmixtures in the concrete can suppress the deleterious expansion induced by thealkali-aggregate reaction effectively. These admixtures can also improve otherdurable properties of concrete and also save cost. So, it will be significant toinvestigate the validity of mineral admixtures in inhibiting the expansion of alkali-aggregate reaction and to design the cementitious materials for preventing theexpansion.In this paper, a variety of testing methods, containing the petrographic method(ASTM C295-08), accelerated test methods (CECS48:93), accelerated mortar bar test(ASTM C1260) and field emission scanning electron microscopy (FESEM) have beenapplied to investigate the alkali reactivity of the sand and gravel from the XiangjiangRiver, Hunan comprehensively.The results show that the sand and gravel from Xiangjiang River was composedof greywacke and quartzite, in which there are much more cryptocrystalline an dmicrocrystalline quartz that poorly crystallized with a high potential alkali reactivity.The results of ASTM C1260indicated that all of the aggregates in Xiangjiang Riverare alkali reactive with the expansion more than0.1%. These conclusions have als obeen confirmed by the scanning electron microscopy with energy dispersive X-rayanalysis (EDXA). Some cracks have been observed on the surface of aggregate andaround them. And the morphology of the product are typical, was confirmed asalkali-silicate (ASR) gel with the supplemented analysis (EDXA).On the basis of the above experimental results, the effectiveness for preventingASR by adding fly ash and slag power as replacement of cement has been detected.Then, the component of cementitious materials for preventing ASR and contour mapsof expansion were obtained by using the seven-batch factorial design. At the end thesafe zone on the map for preventing ASR expansion were determined.Based on the basic principle of seven-batch factorial design, the regressionequation models for predicting ASR expansion was resolved with the some validatedexperiments correspond to sand and gravel respectively. Then the prediction resultswere compared with the experimental results. The results show that the errors a relower to meet the accuracy requirements of the ASTM C1260specification on one hand, and very good fitting of prediction and experimental results on the other hand,confirming that the factorial design method used for designing cementitious materialsto suppress the ASR expansion has a good validity.This study reveals the sand and gravel from Xiangjiang River have alkalireactivity, should be take it seriously, for which using such aggregate in constructionhas a great possibility to produce deleterio us ASR expansion. During design theementitious material, not only the ASR expansion should be considered, but also theother durable properties of concrete should be taken into account. In this paper, theseven-batch factorial design method was the first time to use in this field, which isnecessary.