Abstract
To improve the application of low-quality aggregates in structural concrete, this study investigated the effect of multi-purpose mineral admixtures, such as fly ash and ground granulated blast-furnace slag, on the performance of concrete. Accordingly, the primary performance of low-quality recycled aggregate concrete could be improved by varying the replacement ratio of the recycled aggregate and using appropriate mineral admixtures such as fly ash and ground granulated blast-furnace slag. The results show the potential for the use of low-quality aggregate in structural concrete.
Highlights
In Japan, a survey conducted in 2018 by the Ministry of Land, Infrastructure, and Transport showed that 74.4 million tonnes of construction waste are annually produced, most of which are recycled in compliance with the related laws and ordinances
With fly ash (FA), the temperature of the mortar was lower; As the replacement ratio of recycled fine aggregate class L increased, the compressive strength of the mortar decreased when FAII was used to substitute fine aggregate, the long-term compressive strength became higher because of the mineral admixture; When blast-furnace slag (BFS) was used as the BB type, the length change rate became low
By using FAII as a fine-aggregate substitute, because higher binder weight increases compressive strength, carbonation could be suppressed; Considering the fresh concrete with low-quality recycled aggregate, even when the replacement ratio was high, the target quality could be satisfied by varying the amount of chemical admixture
Summary
In Japan, a survey conducted in 2018 by the Ministry of Land, Infrastructure, and Transport showed that 74.4 million tonnes of construction waste are annually produced, most of which are recycled in compliance with the related laws and ordinances. RAC is manufactured by mixing a certain amount of recycled aggregate class L; the uses of which are confined to concrete prepared from original mortar or original cement paste that includes toxic elements such as hexavalent chromium. In 2018, the amount of RAC used was 119,000 tonnes, which is equivalent to 0.3% of the concrete recycling rate, while the remaining amount was used as roadbed gravel or backfill materials. It is necessary to clarify the effects of FA and BFS on the performance improvement of RAC class M using recycled aggregate class L in which a decrease in compressive strength and an increase in drying shrinkage was observed [5]. To promote the use of low-quality recycled aggregate for structural concrete, the effect of multi-purpose mineral admixtures such as FA and BFS on the performance of the RAC class M was examined.
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