Effect Of Loading Rate On Mechanical Properties Of Ultrahigh Toughness Cementitious Composites

As a new constructive material, ultra-high toughness cementitious composites (UHTCC) exhibits strain hardening characteristics, prominent crack-controll ability and energy absorption ability, which provide a brand prospect in building under dynamic load. But, most known researches about UHTCC focus on the properties under quasic-static condition. In order to discuss the performance of UHTCC under seismic condition, investigations about compressive behavior and flexural behavior of UHTCC at different loading rates have been done. The experiment programs and conclusions are included:(1) Some common analytical methods of toughness are reviewed in this paper, such as ASTMC1018standard of America, steel fiber reinforced concrete standard(DBV) of Germany, JSCESF4method of Japan concrete institute and so on. By comparing and analyzing these methods, advantages and disadvantages of each one are presented.(2) According to four-point bending tests of UHTCC and its matrix at different loading rates, the influence of loading rate and loading regime on flexural behavior has been discussed, covering the cracking strength, ultimate strength and deflection at peak load. Results indicate that, different indicies of flexural behavior of UHTCC under different loading regimes exhibit different rate sensitivity. UHTCC under the two loading regimes both exhibit eminent micro-cracking ability, but UHTCC under cyclic load shows better cracking ability; Toughness of UHTCC beams under cyclic loading and that under monotonous are almost the same, and toughness of UHTCC beams show steady with loading rates; damage degree of UHTCC beams under cyclic load first increases then decreases with loading rates.(3) Researches about the effect of loading rate on the compressive behavior of UHTCC are conducted through the uniaxial compressions tests on UHTCC and its matrix material. It is shown that the cracking strength, compressive strength and compressive toughness all decrease with the increasing of loading rate. But, loading rate has hardly any effect on the compressive strain corresponding to the peak stress.(4) Some common constitutive models of concrete under uniaxial compression are introduced in this paper. Based on these models and results of compressive tests, a dynamic constitutive models of UHTCC under uniaxial compression is proposed in the paper.