Effect of low volume mineral admixtures on impermeability of shotcrete
The improvement effect of different mineral admixtures(fly ash,slag powder and silica fume)on the impermeability of shotcrete by single mixing or compound mixing under the condition of low volume(from 5%to 10%)were studied.The influence of different mineral admixtures on the setting time of cement pastes mixed with accelerator and compressive strength of shotcrete were also considered.The experiment results show that fly ash and slag powder have little effect on the setting time of cement pastes mixed with accelerator,while silica fume can shorten the setting time obviously.Single mixing or compound mixing of different mineral admixtures under low volume condition will reduce 1 d compressive strength of shotcrete to a certain extent,but the impact is small.Slag powder and silica fume can improve 28 d compressive strength significantly through pozzolanic effect and micro-aggregate effect in the later stage.The water penetration resistance and chloride penetration resistance of shotcrete are characterized by water penetration height,water absorption rate,electric flux and chloride ions diffusion coefficient respectively.Among them,silica fume has obvious improvement effect whether it is single mixing or compound mixing with fly ash or slag powder,however,the improvement effect of single mixing of fly ash or slag powder is general.The research results can provide reference for the application of mineral admixtures in shotcrete.
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