Overview
The aim of this project was to increase knowledge and understanding of green concretes in the context of circular economy (CE), and compare various concrete’s durability and carbon intensity.
Method
Concrete cubes were produced in the lab. The mix designs had been based on a wet-pressed kerb mix. Four sets of trial mixes were prepared, one Ground Granulated Blast Furnace Slag (GGBS), one Pulverised Fly Ash (PFA), one Ground Calcium Carbonate (GCC) and one Ordinary Portland Cement (OPC) control mix. There were four further mixes per set with replacement levels of 25%, 50% and 75%. The control mix provided standard results for ‘normal’ pollution and carbon emissions to compare against the substitutes.
Results
By inputting the trial mixes into the carbon calculation tool, data was gathered on carbon emissions reduction per mix, as shown in figure 6.
Figure 6. Emission reductions compared to OPC
The strength performance of the different trial mixes are shown in figure 7.
Figure 7. Comparison of strength performance for the different trial mixes
Although the GGBS results are very similar to the control OPC mix, these results indicate that its use does not increase the durability of the concrete.
The PFA mixes showed higher strength loss compared to the control OPC mix. High replacement levels would severely decrease the durability of the concrete. This would reduce the lifespan of the concrete and would not fulfil the CE strand of ‘Keeping products and materials in use’.
The use of GCC as a cement replacement in this trial showed significant strength loss against the control OPC mix. This indicates a potentially detrimental impact on durability and performance of the concrete.
Each cement alternative was scored on how well they meet each circularity indicator, and thus contribute to a circular economy. The scoring system is 0 – 10, with 0 being the baseline which is in line with current OPC concrete. Higher scores indicate greater circularity, lower scores less circularity. An example being; A score of 10 shows that the indicator is completely circular with no flaws; a score of 5 shows that the indicator is an improvement on current methods but it may not be completely circular. Negative values are possible if the alternative is worse than OPC.
Figure 8. Visual aid for use when evaluating circularity indicators
The ‘Designing out waste and pollution’ and ‘Keeping products and materials in use’ areas of CE are predominantly focused on the pollution aspect of CE. Table 1 and Table 2 show the scores given against each indicator, highlighting the differences between the trial mixes.
Table 1. Circularity indicators ‘Designing out waste and pollution’ scores
Table 2. Circularity indicators ‘Keeping products and materials in use’ scores
Comparing green concretes in the context of CE involves thorough understanding of; how the wastes are produced, their emissions factors and their performance in concrete. The most circular of the green concretes is GGBS, followed by PFA and finally GCC. However, the result of this study suggests that even though these materials contain circular credentials, they are far from being considered wholly circular.
Danielle Dawson comments
“I'm currently working within the cement division, exploring cutting edge technologies on how we can decarbonise our industry. The BSc has equipped and encouraged me to challenge the industry, making me confident in my knowledge”
Celebrating 10 successful years of the Honours Degree in Mineral Products Management
Throughout April, discover the innovative projects driving change in the mineral products industry, led by recent graduates of the BSc (Hons) in Mineral Products Management:
These cutting-edge projects highlight the next generation of industry leaders, applying their skills to deliver practical, sustainable, and financially beneficial solutions.
For further details on any of the projects or the honours programme covered within this article please contact j.austin@derby.ac.uk