Fresh properties of recycled aggregate concrete

Abstract This investigation intends to characterize the fresh state behaviour of concrete produced with coarse recycled aggregates (CRA). The concrete mixes were produced with different CRA crushing levels (primary crushing or primary and secondary crushing), water to cement (w/c) ratios (0.35, 0.45, 0.55), and paste volumes (±1.25%, ±2.5%). The fresh concrete mixes were tested for slump, flow table, inverted cone, and Vebe. In addition, the workability loss over time was assessed after 0, 30, 60 and 90 min of mixing. The compressive strength of concrete mixes produced after 0 and 90 min of mixing was also related to the workability loss of concrete. The experimental results showed that mixes with CRA and w/c 0.55 tend to have a similar behaviour. This is mainly because in this type of concrete the cement paste plays the dominant role in terms of workability. In mixes with lower w/c (0.35 and 0.45), the shape and texture of CRA became more relevant, leading to less fluidity and consistency. The mixes also showed small scatter of their fresh-state properties for small variations of cement paste volume. For mixes produced with CRA that underwent primary crushing only, the conclusions presented before are valid but the differences are greater.