模拟海洋地材UHPC内源氯离子临界含量及其服役寿命预测

Critical content of endogenous chloride ion and service life prediction of simulated marine materials UHPC

通过内掺不同含量的氯离子模拟制备海洋地材超高性能混凝土(UHPC),采用线性极化法、交流阻抗法和循环极化法3种电化学方法研究了UHPC中钢筋锈蚀时的临界氯离子含量;通过氮吸/脱附试验探究了UHPC的孔结构,最后根据Fick第二定律推导的氯离子扩散模型对模拟海洋地材UHPC的服役寿命进行预测.结果表明,现行规范对海砂混凝土氯离子规定并不适用于UHPC;UHPC中钢筋可发生钝化的内掺临界氯离子质量分数为1.2%~1.9%,远大于普通混凝土氯离子规范限值;UHPC内部结构极为致密,水化后期孔隙率大大减小,与普通UHPC相比,模拟海洋地材UHPC的总孔体积更小,表现出更为致密的微观结构;模拟海洋地材UHPC相对普通UHPC的耐久性能略有下降,但仍具备优异的护筋性能;保护层仅需15 mm,其预测寿命便可达100 a以上.

Simulated marine material ultra-high performance concrete(UHPC) was prepared by incorporation of different contents of chloride, and the critical endogenous chloride ion content of steel bar corrosion in UHPC was studied by three electrochemical methods, linear polarization, electrochemical impedance spectroscopy and cyclic polarization. The pore structure of UHPC was studied by the nitrogen adsorption and desorption test. Finally, the chloride ion diffusion model derived from Fick’s second law was used to predict the service life of UHPC. The results show that the current specification for chloride in sea sand concrete is not suitable for UHPC;the critical endogenous chloride content in UHPC is 1.2% to 1.9% of cement mass, and its conservative value is significantly greater than the standard limit for ordinary concrete chloride ion. The internal structure of UHPC is extremely dense, and the porosity at the late hydration stage is greatly reduced. Compared with ordinary UHPC, the total pore volume of simulated marine ground material UHPC is smaller, showing a more compact microstructure. The durability of UHPC made with simulated marine materials is slightly decreased compared with the ordinary UHPC, but still has an excellent protection property of reinforcement. The predicted service life can reach more than 100 years with the cover thickness of only 15 mm.