Material behaviour and flexural performance of low carbon concrete beams containing very high quantities of recycled and secondary materials

• Published in: Construction & building materials 2023-12, Vol.407, p.133350, Article 133350
• Main Authors: Santorsola, Jordan, Butler, Liam J.
• Format: Article
• Language: English
• Subjects: Coarse recycled concrete aggregates; Fine recycled concrete aggregates; Flexural testing; Ground granulated blast furnace slag; Low carbon concrete; Reinforced concrete beams
• ISSN: 0950-0618
• DOI: 10.1016/j.conbuildmat.2023.133350

•Concrete with up to 70% recycled materials had mean compressive strengths of 30 MPa.•Novel mixture design and batching methods enhanced low carbon concrete performance.•Normal and low carbon reinforced concrete beams had similar flexural capacities.•CSA A23.3 provisions overestimated flexural capacity of low carbon concrete beams.•CSA A23.3 provisions underestimated maximum deflection of low carbon concrete beams. As the global urban population continues to grow, reducing the carbon footprint of our built environment is on the critical path towards achieving net-zero CO2 targets by 2050. Representing the largest contributor to infrastructure-related emissions, the cement and concrete sectors are accelerating their efforts to develop low carbon concrete structures. In line with this critical path, this paper presents a first of its kind study on the performance of reinforced concrete beams produced using concrete containing very high quantities (greater than 80%) of recycled and secondary materials. A total of 24 low carbon concrete mixtures were developed and evaluated. Mixtures included the use of coarse and fine recycled concrete aggregates (100% replacement of natural aggregates) and the use of ground granulated blast furnace slag (50% replacement of portland cement). Using a combination of novel mixture proportioning and two-stage mixing methods, mixtures were adjusted to improve compressive strength, workability, and batch-to-batch consistency. Several low carbon concrete mixtures containing greater than 70% recycled and/or secondary materials achieved compressive strengths of approximately 30 MPa. Twelve reinforced concrete beams (2.25 m) were tested in four-point bending. Reinforced concrete beams produced with low carbon concrete with up to 89% recycled and/or secondary materials had ultimate moment capacities which were, on average, only 5% lower compared to the conventional concrete beams. Current CSA A23.3 design equations were conservative in their estimates of ultimate moment capacity for both the conventional and low carbon concrete beams.