(I07) The Vagaries of Low-Carbon Concrete

The built environment’s reinforced focus on carbon has placed considerable attention on concrete. As a key driver of embodied carbon of structures, concrete is often the first avenue where designers and builders seek to reduce carbon by optimizing mix designs. This typically involves reducing cement in mix designs by using supplementary cementitious materials (SCMs), admixtures, better quality aggregate, or substituting with blended cements. Several performance requirements also need to be met while reducing carbon – compressive strength at multiple milestones, shrinkage, finish, workability, and more as needed. ‘Performance-based’ specifications are touted as the best practice to ensure these outcomes, but during both design and execution - pursuing low-carbon concrete presents various challenges. In this session, we’ll discuss a variety of these challenges and how to prepare for them. These lessons are based on experience from several projects that implemented low-carbon concrete mix designs. We'll share perspectives from the key players involved in delivering such projects - a ready-mix concrete supplier, a structural engineer, a general contractor, and a sustainability consultant. The following types of challenges will be discussed by the panel: Cost: - Increased testing and inspections - Increased labor hours due to longer curing times - Increased material cost for admixtures Logistics: - SCM availability - Impacts on daily and overall schedules Performance: - Shrinkage - Workability - Finished aesthetic Specifications - Setting appropriate targets for Global Warming Potential (GWP) - Uncertainty about implications for bidding process While there is sufficient informational content about technical resources on this topic, this session will advance the conversation with real-world lessons and tips. We will include an interactive element asking members of the audience to share their own experiences. We hope that the panel’s insights will both inspire the audience to implement low-carbon concrete and prepare for challenges that might await.