CALTRANS: Impact of the Use of Portland-Limestone Cement on Concrete Performance as Plain or Reinforced Material - Final Report

This work develops a Bayesian model that can be used to proportion sustainable, resilient, and cost-effective concrete mixtures based on stakeholder preferences. Traditionally, the decision-making process for proportioning concrete mixtures is centered around meeting target specifications, such as slump and compressive strength, and attributes such as sustainability and durability are given minimal importance. However, in the global push towards green infrastructure, sustainability plays a major role and must be considered to the same degree as engineering attributes. The model developed herein accounts for embodied carbon footprint, cost, and time to corrosion initiation, apart from the target specifications commonly used to proportion concrete mixtures. The developed model is demonstrated through two case studies: one targeting the average industrial embodied carbon footprint for a concrete mixture and the other targeting a reduction of 40% from the industry’s carbon footprint average. This model can also be used to perform data visualization and sensitivity analyses.

The ordinary Portland cement (OPC) component of concrete is the highest contributor to concrete’s cost and carbon footprint. Historically, code-writing organizations have required a high volume of paste in concrete mixtures by imposing minimum limits on the OPC content for a given application. However, high paste contents can result in dimensional instability, higher costs, higher carbon footprints, and lower durability. Minimizing the OPC content in concrete can provide economic, durability, and sustainability benefits. This study hypothesizes that the amount of OPC required to achieve some required fresh and hardened characteristics is highly dependent on the aggregate characteristics, supplementary cementing material (SCM) characteristics, and proportions of these. Given this, this research proposes using the amount of voids in the aggregate system (AV), or more specifically the paste volume-to-aggregate void ratio (PV/AV); SCM reactivity; and the SCM replacement level as key parameters to proportion concrete mixtures with minimum OPC contents to meet sustainability, economic, and resilience (SER) requirements. A new mixture proportioning procedure, referred to here as the SER proportioning method, is developed in this study based on assessing AV and identifying an optimal PV/AV that satisfies the required concrete characteristics. The results show that implementing the SER mixture proportioning method and including SCMs, or more specifically off-spec fly ashes (OFAs), can lead to significant reductions in the paste content and associated reductions in the cost and embodied carbon footprint of concrete.