A Comparative Life Cycle Assessment of Ordinary Portland Cement, Limestone Calcined Clay Cement and Mining Waste Marl Cement

Abstract

Morocco aims to decarbonise its cement subsector, responsible for 91% of domestic industrial CO2 emissions. To that end, clinker reduction figures among the main strategies listed in the Nationally Determined Contribution (NDC) put forward by the country in 2021. Clinker reduction can be achieved through its substitution with supplementary cementitious materials (SCMs). One type of SCM widely available in Morocco is marl, abundantly deposited in Moroccan phosphate mines. Valorising phosphate marl as an SCM in cement production will thus reduce cement-related CO2 emissions while bringing an element of circular economy to the table. To estimate the environmental potential of this solution and benchmark it against existing cements, a comparative life cycle assessment (LCA) of ordinary Portland cement (OPC), calcined marl cement (CMC) and limestone calcined clay cement (LC3) has been conducted. The first part of the study is a cradle-to-gate LCA of 1 ton of cement. Results show that CMC and LC3, due to their lower clinker content, respectively emit 22% and 42% less CO2 than OPC. In the second part of the study, durability and compressive strength are quantified and then considered in an upgraded functional unit: 1 ton of cement per MPa per year. Results show that CMC and LC3 this time emit respectively 29% and 70% less CO2 than OPC. A sensitivity analysis of the results to the choice of the impact method was carried out. The disparities between Impact World+ and ReCiPe 2016 illustrate the importance of interpreting LCA results in light of the chosen impact method.