Rheology and mechanical properties of limestone calcined clay based engineered cementitious composites with nano CaCO3

The application of binder consisting of limestone, calcined clay and cement (LC³) promotes the development of low-carbon engineering cementitious composites (ECC). In order to improve the comprehensive properties of LC³-ECC, this paper investigates the feasibility of using nano CaCO₃ (NC) to replace the limestone powder up to 20% for LC³-ECC preparation through rheology and mechanical tests along with the micro-design calculation and microstructure analysis. Results indicate that the yield stress and plastic viscosity of LC³-ECC are largely improved with increasing NC replacement rate. Meanwhile, the compressive, flexural and tensile strengths of LC³-ECC with NC raise firstly and then decline, while the strengths are maximum at NC replacement rate of 5% but the tensile strain capacity remains at 2.3%. The hydration promotion effect and pore structure refinement effect of NC particles improve the mechanical strength of LC³-ECC, but the performance degradation occurs when the replacement rate of the NC exceeds 10%. In micromechanics, the fibre bridging stress of LC³-ECC reinforced by NC with replacement rate of 5% decreases by 18.5% compared to that of without NC, but it grows with the increasing NC replacement rate. In combination with fresh, hardened and microstructure behaviour, LC³-ECC exhibits the optimum mechanical behaviour with the NC replacement rate of 10%–15%.