Linkage of multi-scale performances of nano-CaCO3 modified ultra-high performance engineered cementitious composites (UHP-ECC)

This paper investigated the effects of nano-CaCO3 (NC) with different contents (i.e., 0-4% by mass of cement) on hydration, micro-structure and mechanical properties of ultra-high performance engineered cementitious composites (UHP-ECC) and clarified the inherent relations of multi-scale performances of UHP-ECC. At the micro-scale, the heat evolution analysis was firstly conducted and the results showed that NC accelerated the heat of hydration of UHP-ECC matrices due to its nucleation and dilution effect. Then, the phase developments of NC modified UHP-ECC matrices were discussed using the thermal gravimetric analysis/differential thermal gravimetric analysis, which proved the filler effect of NC. Mercury intrusion tests (MIP) indicated that not only the porosity but also the critical pore size decreased with the increase of NC content up to 3%, beyond which the porosity increased due to the agglomerate of NC. Finally, the morphologies of ultra-high molecular weight polyethylene fiber surfaces and fiber-matrix interfaces were observed by scanning electron microscope. At the meso-scale, single fiber pullout tests were conducted and verified that the frictional stress between fiber and matrix reached the maximum value with NC content of 3%, which was in accordance with the results of MIP tests. At the macro-scale, the optimal NC dosage to enhance the compressive, tensile and flexural properties of UHP-ECC was found to be 3%, which was strongly supported by the results obtained at micro- and meso-scale. Hence, intense linkages between the micro-, meso- and macro-scale performances of UHP-ECC were exhibited, and the micro- and meso-scale properties induced a decisive impact on the mechanical properties of UHP-ECC at composites level. (C) 2019 Elsevier Ltd. All rights reserved.