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

The application of advanced 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 %.