Switching to Portland Limestone Cement Could Reduce Emissions

A life-cycle assessment of PLC shows a 12% improvement in environmental performance over ordinary portland cement (OPC) when used in concrete mixes.

Cradle-to-gate life cycle impacts of PLC

and OPC

Cradle-to-gate life cycle impacts of PLC and OPC

Results of the assessment show that PLC has a lower environmental profile than OPC across all impact indicators.

Source: Athena Sustainable Materials Institute

The Athena Sustainable Materials Institute recently prepared a life-cycle assessment (LCA) for the Cement Association of Canada confirming assumptions about the lessened environmental impact of portland limestone cement (PLC) relative to ordinary portland cement (OPC).

Results of the assessment indicate that PLC (cement mix with high limestone content) reduces greenhouse gas emissions by 9.6% compared with OPC mix. The argument that PLC could help reduce the environmental impact of concrete has long been proposed based on what was logically deduced from substituting more limestone for less clinker—the ingredient that is most responsible for cement’s CO₂ emissions as well as for the high energy consumption needed during manufacturing—but this study “gives solid numbers to evaluate,” according to Kathrina Simonen, director of the Carbon Leadership Forum, which was not involved in this LCA. The report also finds PLC performed better across all measured environmental impacts, including having a lower ozone depletion potential and lower smog potential.

The assessment is not ISO-compliant because it is constrained to “cradle-to-gate” impacts, so it does not capture impacts during the use phase or end-of-life stages. Still, the work “should support the development of further research,” Simonen told EBN.The authors of the report hope it also drives efforts to increase the levels of PLC allowed by building codes. Since Canadian rules only allow limestone content up to 15%, the report concludes that employing levels “similar to those levels allowed in European codes,” which permit up to 35%, “would go a long way to further improving the industry’s environmental performance.” PLC content is limited to 5% in the U.S. because of concerns that the limestone will affect the strength of the concrete.