article · Environmental Progress & Sustainable Energy
Limestone overburden clay calcined at temperatures between 500 and 800 degrees Celsius offers a viable supplementary cementitious material to partially replace clinker in Portland cement. Testing cement blends containing 30, 50, and 70 percent calcined clay over curing periods from one to 90 days revealed that thermal treatment at 600 degrees Celsius yielded the best results. A mixture incorporating 30 percent calcined clay reached a compressive strength of 40.0 megapascals and a flexural strength of 5.9 megapascals at 90 days, compared to 54.0 and 7.8 megapascals for standard control cement. The calcined material contained over 70 weight percent combined silicon, aluminium, and iron oxides, indicating high pozzolanic reactivity, while maintaining water absorption below 10 percent. Statistical analysis showed replacement levels significantly affected strength, whereas calcination temperature differences were not statistically significant.
Cement manufacturing generates substantial carbon dioxide emissions and consumes large volumes of mined clinker. Utilising limestone overburden clay, a mining byproduct, as a supplementary material can lower clinker requirements, cut emissions, and minimise environmental disruption. Demonstrating that this material meets practical durability and strength standards provides a route toward more sustainable concrete production.
This research demonstrates an applied, laboratory-tested method for cement manufacturers looking to reduce clinker consumption and carbon dioxide emissions by using calcined overburden clay. Because the material can replace up to 30 percent of clinker while maintaining acceptable strength and low water absorption, it offers a direct pathway for industrial trials. Further pilot-scale testing and standardisation would be needed before commercial deployment in construction products.
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Abstract Calcined limestone overburden clay was investigated as a supplementary cementitious material (SCM) for partial clinker replacement. Cement blends containing 30%, 50%, and 70% calcined clay, produced at 500–800°C, were cured for 1–90 days and evaluated for mechanical, durability, chemical, and microstructural properties. Calcination at 600°C produced optimum performance, with the 30% replacement mixture achieving 40.0 MPa compressive and 5.9 MPa flexural strengths at 90 days, compared with 54.0 and 7.8 MPa, respectively, for the CEM I control. The combined SiO 2 , Al 2 O 3 , and Fe 2 O 3 content exceeded 70 wt %, confirming substantial pozzolanic potential, while water absorption remained below 10%. Multiple linear regression and ANOVA indicated that calcined clay replacement significantly influenced compressive and flexural strengths ( p < 0.05), whereas calcination temperature was statistically insignificant ( p > 0.05). The models demonstrated strong predictive performance, with R 2 values of 97.96% and 95.00% for compressive and flexural strengths, respectively. XRD and SEM–EDS confirmed quartz and silica‐rich phases in the calcined clay. Overall, limestone overburden clay demonstrates potential as an effective SCM for reducing clinker consumption, CO 2 emissions, and environmental impacts of cement production.
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DOI: 10.1002/ep.70676
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