不同强度等级混凝土遭受超低温冻融循环作用的受压强度试验研究

通过设计强度等级C40、C50及C60混凝土经历0次、16次和30次温度区间分别为15℃~-120℃和15℃~-190℃的冻融循环作用试验，探讨不同强度等级混凝土超低温冻融循环作用下受压强度变化规律。试验结果表明，不同强度等级混凝土试件上下限温度时加载的破坏形态基本上类似、均大致呈对顶锥状，但其破坏面状况等破坏特征有所不同。经历各种超低温冻融循环作用工况混凝土上、下限温度时的相对受压强度随其含水率增加基本上均呈下降趋势。而随强度等级提高，上限温度时混凝土相对受压强度呈增大态势，但各强度等级混凝土均随冻融循环作用次数的增加呈下降趋势；下限温度时不同超低温温度区间的混凝土相对受压强度虽也基本上有所增大，但增大的原因存在明显的差异。给定的超低温冻融作用温度区间工况下各强度等级混凝土下限温度时相对受压强度随冻融循环作用次数增加的变化趋势相似，但不同温度区间时却不同。超低温冻融作用对混凝土性能影响与常规冻融作用不同，其受压强度恶化更为严重。实际工程中不能直接地将常规冻融循环作用研究结果应用于设计具有超低温冻融作用的混凝土结构。

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 isobvious difference in the reasons for its increase.The variation trend of the relative concrete compressive strengthwith the increase in the number of freeze-thaw cycles is similar in a given ultralow temperature range regardlessof the concrete strength grade,but there exists a difference between different ultralow temperature ranges.Theinfluence of ultralow temperature freeze-thaw action on the concrete mechanical performance is different fromthat of natural ambient temperature freeze-thaw action,from which the degradation of the concrete compressivestrength is much more serious.In practical engineering,the results from natural ambient temperature freeze-thawaction should not be directly applied to the design of concrete structures that undergo ultralow temperaturefreeze-thaw action.