Are High-Alkali Natural Pozzolans (HANP) Capable of Mitigating Alkali-Silica Reaction in Concrete?

Описание: Presented By: Weiqi Wang, Clemson University
Use of supplementary cementitious materials (SCMs) that are high in their alkali content is generally avoided as a strategy to mitigate Alkali-Silica reaction (ASR) in concrete. The reason being the alkalies in SCMs may supplement the alkali-loading in concrete, which may exacerbate the problem. However, in light of growing need to find suitable alternatives to high-quality fly ashes that meet ASTM C618 specifications, this study investigates the validity of the premise that high-alkali SCMs may be ineffective in mitigating ASR. Further, the study also explores the validity of standard test methods such as ASTM C1567, C1293 and AASHTO T380 in evaluating such high-alkali SCMs. For this purpose, 6 high-alkali natural pozzolans (HANP) and 2 reclaimed fly ashes (RFA) that have high total alkali content were selected. Using an established reactive aggregate, these SCMs were evaluated in the aforementioned test methods, to assess their effectiveness in mitigating ASR. In the next stage, we plan to measure the total and the available alkali content of these SCMs along with the pore solution composition to assess the alkali leaching from the SCMs. Further, the pozzolanic reactivity of these SCMs along with their ability to bind alkalies in the cementitious matrix will be evaluated to quantitatively predict their ASR mitigation. Results to date indicate that vast majority of the HANPs are effective in mitigating ASR, while the performance of RFAs in highly variable. Also, modifications to existing test procedures needed to more precisely assess the ASR mitigation performance of high-alkali pozzolans will be presented.