Improved mechanical properties and fiber dispersion of limestone calcined clay cement (LC³) mortars by adjusting the mixing methods

An emerging cement, limestone calcined clay cement (LC³), reduces CO2 emissions by using less clinker in manufacture, promoting sustainability. Compared with OPC, LC³ binders (with the same water-to-binder ratio) show reduced flowability, leading to poor fibre dispersion in the matrix. This paper attempts to improve the flowability by adding different amounts of superplasticizer and using an innovative two-phase water addition (TPWA) mixing approach. This method focuses on adjusting the amount of water addition in the first phase to improve the fibre distribution while maintaining the total water addition for all mixtures. Results show that modified mixing strategies improve the fresh and hardened characteristics of LC³ mortars. As the amount of water addition (in the first phase) decreases, the yield strength increases while the plastic viscosity of mortars decreases. The high yield stress is associated with high fibre segregation resistance during the compaction. The low plastic viscosity is related to high fibre mobilizability during mixing, preventing fibres from clustering. As a result, the humongous mixture and the best mechanical performance was achieved when 83 % of the total water was added in the first phase, with a w/b ratio of 0.35. For the mixture with a w/b ratio of 0.38, the best mechanical properties were obtained when 68 % of the total water was added in the first stage. The relationships between rheological properties, fibre dispersion and mechanical properties of LC³ systems are also established.