Activated clays as supplementary cementitious material

Concrete is the most used material in the world (buildings, infrastructure, transport) and its production is continuously increasing over the years because of the growth of the population, the urbanisation, and the infrastructure development. Unfortunately, the production of the main component of concrete, cement, causes inevitable CO2 emissions, accounting for 6% of the total anthropogenic CO2 emissions. The most efficient way to reduce this environmental footprint is to reduce the clinker factor in cement or to reduce the cement content in concrete, which is done by replacing a part of the cement by Supplementary Cementitious Materials (SCM). However, the most commonly used SCM (fly ash and ground granulated blast furnace slag) are only available in a low amount in Sweden. New SCM must be find.The objective of this project was to evaluate the potential of using Swedish clays as SCM. An inventory of available clays was performed in a first step. Then, as clays need to be activated before use with cement, different activation procedures were tested. A selection of clays was mixed with cement either in binary mixes (cement + activated clay) or in ternary mixes (cement + activated clay + limestone). The hydration properties and the microstructure of binder pastes were investigated, as well as the strength development of mortars. Finally, a life cycle analysis (LCA) was performed to evaluate the positive impact on the CO2 emissions when clays are used as SCM.The results of the project highlighted the good potential of using Swedish clays in concrete to decrease the environmental footprint due to the cement and concrete industries. In particular, the clays can be activated through mechanical and thermal treatment, depending on the type of clay. Thermal treatment in temperature ranges between 600-800 degrees is preferred for sedimentary clays, while a mechanical treatment by ball milling gives better results with marine clays. A satisfactory strength is achieved in mortar samples cast with calcined clays. This was achieved by replacing the cement with 30% of calcined clay and 15% of limestone. Finally, the LCA calculation shows that the use of clay in a ternary binder lead to a reduction of approx. 34% of the CO2 emissions