CONCRETE PAVEMENT SUSTAINABILITY: OPTIMISING MIX DESIGN FOR DURABILITY PART 4

The following presentation was delivered as part of the 2023 American Concrete Institute (ACI) Concrete Convention hosted in San Francisco.

This presentation by Milena Ramgoolam from Vital Metrics was on the topic of Concrete Pavement Sustainability: Optimising Mix Design for Durability. This is the Part 4 of a four-part article.

… continued from Part 3.

Multi-faceted environmental benefits

Beyond the reduction in global warming potential (GWP), optimising mix designs for paste content reduction and improved aggregate gradations brings about positive changes in various environmental impact categories. From ozone depletion and smog creation to eutrophication and acidification, the overall environmental footprint improves.

Correlations with durability and performance metrics

The second half of our presentation focuses on correlations with durability and performance metrics, as detailed in a recently published paper. This study aims to dispel misconceptions surrounding the trade-off between reducing carbon emissions and compromising durability. It draws on data from four different studies, including the previously discussed MCTC data, Turner, CP Tech Centre, and the University of Florida, covering a total of 145 concrete mixtures.

Methodology and parameters

The comprehensive analysis incorporates various mix types, paving and structural, with diverse supplementary cementitious materials, water-cement ratios, and paste contents. The methodology involves standard tests for compressive strength, surface resistivity as a proxy for durability, and life cycle assessments (LCA) to correlate mix design parameters with embodied carbon and mechanical and durability properties.

Addressing stakeholder concerns

This study emerges from a dedication to addressing stakeholders’ concerns and dispelling misperceptions. It seeks to answer whether reducing carbon emissions in concrete mixes inevitably leads to a deterioration in durability. By examining a wealth of data across different mixtures and parameters, the study aims to provide evidence-based insights that guide sustainable practices in concrete pavement construction.

Concluding insights

As we conclude this presentation, let’s recap the key findings and insights derived from our extensive study on the correlations between mix design parameters, embodied carbon, and the mechanical and durability properties of concrete:

• Cement content and global warming potential (GWP): A strong correlation: The graph depicting cement content versus global warming potential reveals a robust linear trend, emphasising the significant impact of cement on environmental sustainability. The demand for more granular data for cement becomes evident, and ongoing research endeavours are addressing this need.
• Mix design variations and environmental impact: Examining different mixes, including those with ordinary Portland cement and Portland limestone cement, reaffirms the strong correlation between cement content and GWP. The inclusion of Portland limestone cement showcases a proportionally lower environmental impact, providing a promising avenue for sustainable concrete solutions.
• Compressive strength and GWP: Breaking conventional wisdom: Contrary to conventional wisdom, our analysis challenges the notion that higher compressive strength inevitably leads to higher GWP. The data reveals a diverse and non-linear relationship, dispelling common assumptions about the trade-offs between strength and environmental impact.
• Paste content optimisation for sustainability: One graph illustrated the effect of paste content on the composite parameter of compressive strength over GWP, highlights the trade-off point around 25% paste content. This serves as a practical guideline for optimising mixes for both strength and sustainability.
• Durability and environmental sustainability: A synergistic relationship: The correlation between surface resistivity (a proxy for durability) and GWP demonstrates a trend where mixes with higher surface resistivity tend to have lower GWP. This suggests a potential synergy between achieving durability and environmental sustainability.

Conclusion and future directions

In conclusion, our study underscores the importance of considering multiple goals in synergy rather than as conflicting priorities. Cement content remains a significant factor in environmental impact, and optimising mix designs can lead to substantial reductions in embodied carbon without compromising performance.