碳化高温后普通混凝土抗压强度及孔结构演化规律

Evolution Law of Concrete Strength and Pore Structure After Carbonization at High Temperature

混凝土建筑物在服役期间会经历碳化,也可能遭受火灾,双因素共同作用对混凝土结构的影响远大于单一因素的影响。通过X射线衍射法(XRD)、热重法(TG)、压汞法(MIP)揭示了不同碳化时间和温度对混凝土抗压强度的影响机理;采用灰熵分析方法分析了不同孔结构对抗压强度的影响。结果表明:碳化对经历不同温度的混凝土孔结构起到细化作用,提高抗压强度,尤其是在碳化中期、高温400℃条件下效果最佳;碳化高温后阈值孔径、孔隙率整体呈现减小趋势,小孔数量增多,密实度增加,对抗压强度的影响从大到小为阈值孔径、孔隙率、临界孔径;碳化高温后中型毛细孔占比减小,大毛细孔和凝胶孔占比增大,抗压强度与凝胶孔数量呈正相关。

Concrete buildings may be suffered from carbonization and fire during application period.The combined effect of two factors on concrete structures is far greater than that of single factor.The methods of X-ray diffraction(XRD),thermogravimetry(TG)and mercury injection(MIP)were used to research the influence mechanism of carbonation time and temperature on the compressive strength of concrete.Grey entropy analysis was used to analyze the effect of different pore structures on compressive strength.The results show that the pore structure of concrete at different temperatures can be refined through carbonation,and the compressive strength can also be improved,especially in the middle period of carbonation with concrete under 400℃.After carbonization at high temperature,the threshold pore size and porosity of concrete show a decreasing trend,the number of small pores increases,and the density also increases.The influence on compressive strength from large to small is threshold pore size,porosity,critical pore size.At the same time,the proportion of medium sized pores decreases,while those of the large pores and gel pores increase.The compressive strength is positively correlated with the number of gel pores.