疲劳荷载与冻融循环耦合作用下季冻区路面水泥混凝土孔结构研究

Pore Structure Research on Pavement Cement Concrete Subjected to Coupling Effect of Fatigue Load and Cyclic Freeze-thaw in Seasonally Frozen Ground Region

为了探索季冻区路面水泥混凝土孔结构在荷载及冻融作用下的损伤及演化规律,设计了应力水平为50%的疲劳荷载与-18℃-5℃温度范围的冻融循环耦合作用试验方案,研究耦合环境下混凝土孔结构的变化及损伤。采用压汞法和光学法对不同耦合阶段的混凝土孔结构进行定量表征,并结合SEM分析孔结构的损伤演化机理。结果表明：耦合作用下混凝土孔结构的演化分为前期压缩和后期分裂2个过程,压缩过程主要为无害孔（孔径小于20nm）被压缩,孔隙率减小、小孔扩展;分裂过程为多害孔（孔径大于200nm）分裂为有害孔（孔径50-200nm）,孔隙率增大、更多小孔成核;混凝土在破坏时最可几孔径趋于38.6nm,孔间距系数达到0.279mm;耦合作用中的疲劳荷载是造成孔结构劣化的主要原因,冻融循环在耦合后期对孔结构损伤显著。

To explore the damage and evolution rules of pore structure of pavement cement concrete under the effect of load and freeze-thaw in seasonal frozen ground region, a coupling testing program including fatigue load with a stress level of 50% and freeze thawing cycle within a temperature range of --18℃ to 5℃ was designed, and the variations and the damage of pore structure of the pavement concrete under the coupling conditions were investigated. Mercury intrusion method and optical method were used to quantitatively characterize the pore structure of pavement concrete in different coupling stages, and the damage evolution mechanism of concrete pore structure was analyzed combining with SEM images. The results show that the damage evolution process of concrete pore structure under the coupling effect is divided into 2 processes, which is early compression and late fission. In compression process, the innocuous pores （porediameter 〈20 nm） are mainly compressed, consequently the porosity decreases and pores dilate. In fission process, the more harmful pores （pore diameter ）200 nm） are mainly divided into harmful pores （pore diameter 50-200 nm）, the porosity increases and there are more pore nucleations. When the concrete is destroyed, the most probable pore size tends to be 38.6 nm and the coefficient of pore spacing reaches 0. 279 mm. In addition, the fatigue load plays a major role in the process of pore structure deterioration under the coupling effect, and the cyclic freeze-thaw causes significant damage to the pore structure in the late coupling stages.