EXPERIMENTAL STUDY ON THE COMPRESSIVE STRENGTH OF CONCRETE OF DIFFERENT STRENGTH GRADES EXPERIENCING ULTRALOW TEMPERATURE FREEZE-THAW CYCLE ACTION

Through experiments of concrete of different strength grades such as C40, C50 and C60 that experiences 0, 16 and 30 cycles of ultralow temperature freeze-thaw cycle action from 15℃ to -120℃ and -190℃, the effects of the strength grades on the concrete compressive strength are discussed. The test results show that the failure modes of the specimens with different concrete strength grades are similar and generally cone-shaped regardless of the loading at the lower or upper limit temperature, but the failure surface characteristics and so on are different. After experiencing ultralow temperature freeze-thaw cycle action, the relative concrete compressive strengths at the lower and upper limit temperatures decrease with the increase in the concrete water content. With an increase in the concrete strength grade, the relative concrete compressive strengths increase at the upper limit temperature, while the relative concrete compressive strength of every strength grade decreases with the increase in the number of freeze-thaw cycles. Although the relative concrete compressive strength in different ultralow temperature ranges increases at the lower limit temperature, there is obvious difference in the reasons for its increase. The variation trend of the relative concrete compressive strength with the increase in the number of freeze-thaw cycles is similar in a given ultralow temperature range regardless of the concrete strength grade, but there exists a difference between different ultralow temperature ranges. The influence of ultralow temperature freeze-thaw action on the concrete mechanical performance is different from that of natural ambient temperature freeze-thaw action, from which the degradation of the concrete compressive strength is much more serious. In practical engineering, the results from natural ambient temperature freeze-thaw action should not be directly applied to the design of concrete structures that undergo ultralow temperature freeze-thaw action.