A Study on Strength and Durability of Mortar Using Low-quality Recycled Fine Aggregate with Accelerated Carbonation

Abstract

Recycled aggregate produced from demolished concrete and waste fresh concrete are classified into three types of quality using the density in oven-dry condition and water absorption ratio in Japan. Among the three types, compared to medium and high quality recycled aggregate (M and H), low quality recycled aggregate (L) can be produced with less energy and cost, and reduces the generation of fine powder by-product. However, concrete made from L have problems are it has lower strength and greater length change due to drying shrinkage. When considering the widespread use of L, these must be improved with less cost. For these modifications, we have been investigating the use of CO2 gas for accelerated carbonation technology. This technology focuses on the carbonation mechanism of concrete and blows CO2 gas on recycled aggregate to carbonate the cement paste that are attached mortar. It has been found that the physical properties of recycled fine aggregate are greatly improved using this technology. Therefore, to investigate the effect of recycled fine aggregate with accelerated carbonation on the hardened samples, we conducted tests on mortars made from that fine aggregate. It has shown that mortar has improved strength and durability due to the reduction of mortar voids attached on recycled fine aggregate. Especially, we reported that there was a large improvement in the out of specification of L (outside of L). There is a difference in amount of fine powder. L contains 3% fine powder, while outside of L contains 12%. We considered that the fine powder influenced the hardened samples. Therefore, in this study we focused on the granularity, such as fine powder of low quality recycled fine aggregate and conducted tests on mortar to compare the difference in the effect of accelerated carbonation modification technology.