Suitability of Clinker Replacement by a Calcined Common Clay in Self-Consolidating Mortar-Impact on Rheology and Early Age Properties

The use of a high amount of calcined clays as cement replacement presents a great challenge in designing self-consolidating concrete. This current attempt evaluates the influence of cement replacement with up to 40 vol.% by a calcined common clay (CC), dominated by 2:1 phyllosilicates in combination with a fixed limestone powder (LP) content on fresh and hardened properties of self-consolidating mortar (SC-M). The fresh properties of SC-M were investigated by mini-slump flow, V-funnel and rotational viscometer measurements. Setting and hardening behavior were observed via dynamic modulus of elasticity and plastic shrinkage. Hydration mechanisms were determined by isothermal calorimetry and thermal analysis. Hardened properties of SC-M were evaluated using compressive strength tests and mercury intrusion porosimetry (MIP). The results revealed a decreased rate of deformability in SC-M when cement is substituted increasingly by CC and a rising superplasticizer (SP) demand, but indicated an improved stability of SC-M even at a higher dosage of SP and hardly any impact on the setting behavior. CC enhanced the precipitation of monocarboaluminate phases and thereby refined the pore size distribution of the binder matrix. SC-M can be produced with up to 40 vol.% CC as cement replacement without having effect on its 28 days mechanical properties.