ACI: Can Concrete with high-volume recycled concrete aggregate be durable?

The American Concrete Institute (ACI) has released a paper called Can Concrete Containing High-Volume Recycled Concrete Aggregate Be Durable?

The document, written by, Seyedhamed Sadati and Kamal H. Khayat, evaluated the effect of recycled concrete aggregate (RCA) on concrete durability. Six RCA types procured from different sources were employed at 30 to 100% placement rates by volume of virgin coarse aggregate.

ACI says: “One fine RCA was also investigated and was used for up to 40% replacement by volume of virgin sand. In total, 33 mixtures were proportioned with these aggregates in concrete made with a binary or a ternary binder system and a watercementitious materials ratio (w/cm) of 0.37 to 0.45.”

These experiment investigated mixtures for frost durability, electrical resistivity, sorptivity, and abrasion resistance. The results indicated that concrete made with up to 100% coarse RCA from an air-entrained source can exhibit frost durability.

According to ACI: “No significant reduction (limited to 3%) in frost durability factor was observed when the fine RCA volume was limited to 15% of total sand. Increase in mass loss due to deicing salt scaling was observed in concrete made with 50% of RCA with high (over 4%) deleterious materials content and high mass loss during soundness test. For a given w/cm and binder type, the use of 50% coarse RCA resulted in up to 32% reduction in electrical resistivity.”

Additionally, the reduction in w/cm from 0.40 to 0.37 and the use of ternary binder containing 35% Class C fly ash and 15% slag proved to be effective. ACI states the results mitigate the potentially negative impact of RCA on sorptivity and abrasion resistance, compared to concrete made without any RCA with w/cm of 0.40 and binary cement with 25% fly ash.

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