Effect Of Thermal Fatigue On Strength And Permeability Of High Performance Concrete

Suffering from high temperature and high humidity in the summer marine environment, bridge pier located in the water level changing zone suffers the alternating thermal and humidity fatigue cycles. Affected by the intense ultraviolet radiation, the surface temperature is high, then immerse into the low temperature of seawater. The temperature and humidity of the alternating thermal fatigue cycle is bound to affect performance of bridge piers. In addition, the piers of Marine engineering structure always use high performance concrete with good durability, in order to reaching more than 50 years age. Based on this, the thermal fatigue effects on the properties of high performance concrete is an extraordinary research topic. Aiming at this problem, using the high performance concrete containing two kinds of coarse aggregate (HPC30, HPC50) and does not contain coarse aggregate of high performance concrete (Ultra-high performance concrete, UHPC), compressive strength, splitting tensile strength as index, capillary water absorption coefficient and the electric flux as indicators, through the test, the effect of thermal fatigue are studied on mechanical properties of high performance concrete and the influence law of permeability resistance. Main work and conclusions are as follows:(1) On the effect of thermal fatigue of high performance concrete compressive strength test, the determination of the number of different thermal fatigue, HPC30, HPC50 and UHPC compressive strength change rules. Results show that HPC30, HPC50 compressive strength are presented first rise after the fall after the thermal fatigue. The compressive strength of UHPC has declined. After 300 times thermal fatigue effect, compressive strength loss rate of UHPC reached a maximum of 31.1%, about HPC30, HPC50 compressive strength loss rate of maximum 7 times and 3.5 times.(2) On the effect of thermal fatigue, the splitting tensile strength of HPC30, HPC50 and UHPC was tested. The results show that the thermal fatigue, HPC30, HPC50 and splitting tensile strength of UHPC all down after rising first. Compared with HPC30 and HPC50, the effect of thermal fatigue on the splitting tensile strength of UHPC damage is more significant.(3) The water absorption of HPC30, HPC50 and UHPC were tested afterthe effect of thermal fatigue Results show that the thermal fatigue, HPC30 and HPC50 capillary water absorption amount per unit area of the overall decline in law, the early capillary water absorption coefficient (the first phase of capillary water absorption coefficient) also showed a trend of decline. Early UHPC capillary water absorption amount per unit area and capillary water absorption coefficient of the whole are rising.(4) The thermal fatigue of high performance concrete under the action of electric flux test and determination of the number of different thermal fatigue, HPC30, HPC50 and the changing rule of the electric flux of UHPC. The results show that the thermal fatigue, HPC30 and HPC50 electric flux of the overall decline trends, the electric flux of the UHPC present the rising trend. Analysis shows that thermal fatigue effect increases the high performance concrete containing coarse aggregate (HPC30, HPC50) resistance to moisture and chloride ion penetration ability, weaken the permeability of UHPC containing steel fiber.