Impact of concrete moisture on the fatigue resistance of high-performance concrete under various load types

Currently, the verification of concrete structures exposed to fatigue is very conservative and does not utilise the possibilities of modern concrete mixtures.For this reason, current research projects are focussing on the fatigue properties of high-strength concrete (HPC) and ultra-highstrength concrete (UHPC).Significant influencing factors such as load frequency, load level, composition, and concrete moisture were identified.Several studies have consistently shown that concrete moisture adversely impacts fatigue behaviour across both low and high test frequencies.This detrimental effect becomes significantly more pronounced when specimens heat up during loading.So far, this phenomenon has been most clearly observed under uniaxial loading conditions.The present experimental study aims to investigate the influence of moisture on different types of loading.For this purpose, fatigue tests were carried out under uniaxial, triaxial and combined shearcompression fatigue loading.The latter was introduced using a special test setup, referred to as refined punch-through shear test (PTST).To reduce the influence of temperature, the fatigue tests were conducted at a test frequency of 2 Hz.The confinement level in both the PTST and triaxial tests was set at 20 MPa, while the corresponding lower load level was 5% of the static shear/compressive strength.The upper load level varied between 75% and 95%.Wet and dried concrete were analysed for all three types of loading.The results emphasize the significant impact of moisture on the number of cycles to failure, which varies substantially with the type of loading.