Behaviour of strain-hardening cement-based composites under high strain rates

In this research project the behaviour of strain-hardening cement-based composites (SHCC) subjected to low and high strain rates was studied. Uniaxial tension tests on dumbbell-shaped SHCC specimens were performed at rates ranging from 10^-5s^-1 to 50s^-1. For the tests performed at strain rates of 10^-2s^-1 and below, SHCC yielded a moderate increase in tensile strength and simultaneous decrease in strain capacity with increasing strain rate. When tested for higher strain rates from 10 to 50s^-1 a considerable increase in tensile strain and strain capacity was measured. Microscopic investigation of the fracture surfaces showed that almost no fibre failure and an average pullout length of 2.5mm were found in the high strain rate test. This observation is in contrast to that of rapid quasi-static testing, where the average fibre pullout length of 300μm was much shorter. Furthermore, the fibres on the fracture surfaces produced in the high rate tests exhibited pronounced plastic deformations. Finally, quasi-static and high-speed tension tests on individual fibres and single fibre pullout tests were performed. While the increase in the tensile strength of the fibre was only moderate in the range of strain rates investigated, a considerable increase in bond strength between fibre and matrix was determined.