高性能湿喷混凝土的抗冻性能及气泡结构特征研究

Research on Freeze-thaw Resistance and Air-void Structure Characteristics of High Performance Wet-mix Shotcrete

通过借鉴混凝土快冻法,对比研究高性能湿喷混凝土(HPS)、掺速凝剂的模筑混凝土(HPS-Cast)及普通喷射混凝土(NSC)的抗冻性能,并对其内部气泡结构特征进行分析。结果表明:冻融循环作用下,NSC相对动弹性模量和抗压强度显著下降。冻融循环125次后,NSC相对动弹性模量仅为51.34%,冻融循环200次后,抗压强度损失率已达到53.30%,相比之下,HPS、HPS-Cast抗冻性能明显优于NSC,其中HPS抗冻性能最好。HPS-Cast由于采用模筑成型,成型方式与HPS不同,造成HPS-Cast气泡分布特征与HPS明显不同。冻融循环过程中,HPS-Cast平均气泡直径、平均气泡面积、气泡间隔系数均明显高于HPS,同时在0~200μm范围内孔体积率下降速率明显高于HPS,而200~500、500~1200μm及大于1200μm孔体积增长速率明显高于HPS。因此在冻融循环过程中,HPS-Cast抗冻性能较HPS下降更为明显。

The freeze-thaw resistance of high performance wet-mix shotcrete(HPS),molded concrete mixed with accelerator(HPS-Cast)and ordinary shotcrete(NSC)was studied by reference to concrete quick freezing method,followed by an analysis on their internal air-void structure characteristics.The results show that the relative dynamic elastic modulus and compressive strength of NSC ordinary shotcrete decrease significantly under freeze-thaw cycles.After 125 freeze-thaw cycles,the relative dynamic elastic modulus of NSC is only 51.34%.After 200 freeze-thaw cycles,the compressive strength loss rate reaches 53.30%.By comparison,HPS and HPS-Cast have better freeze-thaw resistance than NSC,among which HPS has the best freeze-thaw resistance.HPS-Cast,due to using mold casting,has a different molding method from HPS,showing a significantly different air void distribution characteristics from HPS.During the freeze-thaw cycle,the average air void diameter,average air void area and air void spacing coefficient of HPS-Cast are significantly higher than those of HPS.At the same time,the decline rate of pore volume fraction in the range of 0~200μm is significantly higher than that of HPS,while the pore volume growth rate of 200~500μm,500~1200μm and>1200μm is significantly higher than that of HPS.Therefore,the freeze-thaw resistance of HPS-Cast decreases more obviously than that of HPS during the freeze-thaw cycle.