Microstructural evolution and dynamic compressive properties of engineered cementitious composites at elevated temperatures

This paper presents a comprehensive study on the microstructural evolution and quasi-static and dynamic compressive properties of engineered cementitious composites (ECC) at elevated temperatures (20, 105, 250, 400, 600 and 800 °C). Split Hopkinson pressure bar (SHPB) was adopted to investigate the compressive behaviour of ECC at various strain rates after exposure to elevated temperatures, while the corresponding microstructural evolution was characterised using scanning electron microscopy (SEM), digital electron microscope and mercury intrusion porosimetry (MIP) along with fractal analysis. Results indicate that ECC exhibited strain rate effect and high temperature sensitivity simultaneously. The residual dynamic compressive strength of ECC increased by 33.0–50.4% with the rising strain rate from 79.8 to 127.1 s−1. It reached the maximum value at 105 °C but reduced to 14.3−25.8% at 800 °C compared to that at 20 °C. The change in dynamic increase factor of ECC for various temperatures and strain rates can be well predicted using the developed equation. The thermal decomposition of PVA fibres was the main detrimental affecting the dynamic performance of ECC at sub-high temperatures (below 400 °C), whereas the negative effects caused by the formation of pores and microcracks in the matrix dominated at higher temperatures (400−800 °C). Microscopic damage induced by elevated temperatures aggravated the deterioration degree under dynamic compressive load, whilst the larger the difference in the macro/micro pore structural fractal dimension of 2.50/2.67, the greater the temperature softening effect on impact resistance of ECC.