Temporal flowability evolution of slag-based self-compacting concrete with recycled concrete aggregate

The addition of by-products, such as recycled concrete aggregate and ground granulated blast furnace slag, modify the in-fresh flowability of ordinary self-compacting concrete both initially and over time. A detailed study is presented in this paper of 18 mixtures (SF3 slump-flow class) containing 100% coarse recycled concrete aggregate, two types of cement (CEM I or CEM III/A, the latter with 45% ground granulated blast furnace slag), different contents of fine recycled concrete aggregate (0, 50, or 100%), and three different aggregate powders (ultra-fine limestone powder <0.063 mm, limestone fines 0/0.5 mm, and recycled concrete aggregate 0/0.5 mm). The temporal evolution of slump flow, viscosity, and passing ability, and the values of segregation resistance, air content, fresh and hardened density, and compressive strength were evaluated in all the mixtures. The addition of fine recycled concrete aggregate and CEM III/ A improved initial slump flow and passing ability by 6%, due to their higher proportion of fines. Nevertheless, the temporal loss of flowability within 60 min was 5.8% lower when adding natural aggregate and CEM I. Viscosity and air content increased 26% on average following additions of fine recycled concrete aggregate, unlike with additions of ground granulated blast furnace slag. Flowability and strength increased with the addition of limestone fines 0/0.5 mm. According to multi-criteria analyses, the mixtures with CEM III/A, 50% fine recycled concrete aggregate, and limestone fines 0/0.5 mm showed an optimal balance between their flowability (SF2 slump-flow class 60 min after the mixing process), compressive strengths (around 60 MPa), and carbon footprints. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

The addition of fine recycled concrete aggregate and CEM III/A can improve the initial slump flow and passing ability of concrete, while the addition of natural aggregate and CEM I results in less loss of flowability. The addition of fine recycled concrete aggregate increases viscosity and air content, but the addition of limestone fines 0/0.5 mm can enhance the flowability and strength of concrete. Mixtures with CEM III/A, 50% fine recycled concrete aggregate, and limestone fines 0/0.5 mm show an optimal balance between flowability, compressive strength, and carbon footprints.