| Several resource investigations of national key hydraulic projects show that the aggregates from nearby quarries have certain degrees of alkali-silica reactivity (ASR). Therefore, the study of controlling methods for aggregate alkali reactivity is necessary to ensure the durability of concrete projects. AAR is classified into three types by the kind of the harmful mineral in the aggregate, i.e., alkali-silica reaction (ASR), alkali-carbonate reaction (ACR), and alkali-silicate reaction (ASR). Among the three, the concrete structures affected by alkali-silica reaction are always detected around the world.Several concrete structures under running were investigated. The results show that coarse aggregates with mortar bar's expansion ratio between 0.1% to 0.2%, which have always been considered being low alkali-silica reactive, have showed typical signs of ASR in the concrete structures after thirty to forty years running. The investigation shows that it must take more attention to this kind of aggregates.The present study examined the effects of adding high volumes of ground granulated blast furnace slag (GGBS) and/or fly ash on the prevention of aggregate alkali reaction. Five kinds of aggregates with the expansion ratios about 0.1%, between 0.1%~0.2%, between 0.2%~0.3%, between 0.3%~0.4%, and over 0.4% were examined by accelerated mortar-bar method.The experimental results indicate that all the three kinds of mineral admixtures have the inhibiting effect on ASR. The more the admixtures added, the better effect is obtained. When more than 40% by weight of GGBS, or 20% of fly ash, or 40%~ 60% of the sum of GGBS and fly ash was added into the cementitious materials, the 14d's expansion ratio of the natural aggregates mortar bar is reduced by more than 75%, and 28d's expansion ratio is reduced to lower than 0.10%.When the volumes of the fly ash and the GGBS are same, the inhibiting effect of the fly ash is better than that of the GGBS. However, since the volumes of fly ash in concrete are limited, its volumes are always stipulated below 30%. When the volumes of fly ash is 25%, the inhibiting effect is lower than that with 60% GGBS. When GGBS and fly ash are added simultaneously, and the sum is 60%, the best effect is obtained.The analysis of paste pore solution proves that the effects of ions in the paste pore solution (such as OH~-,K~+,Na~+) on the alkali reactivity decrease rapidly by adding different cementitious materials. The more substances added, the better effect is obtained. GGBS can substantially reduce the concentration of these ions, especially for OH~- and K~+. Adding fly ash can also reduce the concentration of these ions, but it has the best effect on OH~- and Na~+. When GGBS and fly ash are added at the same time, it can reduce more OH~- than adding only fly ash or GGBS.The harmful pore is reduced more than 49% when adding the mineral materials.The inhibiting effect of GGBS on ASR has been proved by SEM.When the compressive strength is same, the concrete added with the mineral materials, which has been approved having inhibiting effect on ASR, has high freezing-thaw durability, and its water permeating resistance is better than the blank concrete. The results indicate that adding mineral materials into concrete is benefit for the concrete durability.
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