气体渗透性作为耐久性指标运用在土木工程领域已经得到广泛认可。一方面，气体在水泥基孔隙材料内部传输过程是耐久性研究的基础问题，另一方面，气体渗透性也是反映水泥基材料的孔隙结构对外部介质侵入的抵抗能力。本文以气体在孔隙材料中的渗流规律为出发点，开展了气体在不同孔隙材料内部渗流的理论、试验和模型研究，并探讨了气体渗透性测试的标准化试验方法。论文研究了气体在孔隙材料中传输中的基本流动模态，包括粘性流、边界滑流和努森流，分析了孔隙尺寸、压力、温度和渗流气体种类对流动模态的影响，并建立了考虑孔隙尺寸分布的平行束管模型。在非稳态流动过程中，本文利用了气体在孔隙材料中传输的本构方程，模拟得到气体流动过程。比较工程中常用水泥基材料，本文制备了四种水胶比（w/b=0.3、0.4、0.5和0.6）的硬化水泥浆、砂浆、混凝土（普通硅酸盐混凝土、30%粉煤灰掺量混凝土和50%矿渣掺量混凝土）。分别利用比重法试验、压汞试验、等温脱吸附试验以及表面扫描试验全面表征了材料的孔隙结构。研究了矿物掺和料对孔隙率、特征孔径、尺寸分布和孔隙分形维的影响。测量了6种目标饱水度（100%：W100、80%：W80、60%：W60、40%：W40、20%：W20和干燥：W0）条件下的材料气体渗透性，分析了气体渗透性之间的组内误差和组间误差。本文使用考虑孔隙尺寸分布的平行束管模型，利用多峰高斯分布表征压汞试验获取的硬化水泥浆的孔隙尺寸分布，在保证本征渗透性与试验值一致的前提下，模拟了本征流、边界滑流和努森流对材料表观气体渗透性的贡献。研究显示：（1）在非稳态条件下，随着材料饱水度增加，模拟气体平衡过程和实际气体平衡过程之间差异逐渐增加。（2）一般情况下，材料气体渗透性的组内误差大于组间误差：干燥条件下，材料气体渗透性的组内组间误差分别可控制在30%和10%以内，但随着孔隙饱水度增加，组内误差增加明显，但组间误差增加不明显；（3）与实测值相比，利用考虑孔隙尺寸分布的平行束管模型得到的模拟值在干燥状态下的误差在10%以内，含水状态下的误差在20%以内；（4）当材料处于含水状态下，通过考虑临界孔径、水膜厚度等因素获得了水膜和未被水分占据的气相孔隙的分布曲线，并建立曲折度放大因子计算表达式。
Gas permeability has been widely used as a durability indicator in the field of civil engineering. On one side, gas transport in cement-based materials is the basis of durability issue. On the other side, gas permeability also reflects materials’ capacity of resisting external media intrusion. This paper studied the permeation law and corresponding theories and models were developed. Moreover, standard gas permeability test methods were also discussed.Firstly, the basic flow modes of gas transport in porous materials, which include viscous flow, boundary slip flow and Knudsen flow, was investigated. Then the paper analyzed the impact of pore size, pressure, temperature and seepage gas species on flow modes, and established the parallel bundle model which considered pore size distribution. Finally, the research built a constitutive equation of gas transport in porous materials and the equation was used to simulate the gas flow. Following frequently-used cement-based materials, hardened cement pastes (HCPs), mortar and concrete specimens with different w/b ratios (0.3, 0.4 and 0.5) were prepared, and the binder of concrete included 100%Portland, 70% Portland+ 30% fly ash, 50% Portland+ 50% clinker. The pore structure of materials was characterized respectively by specific gravimetry method, mercury intrusion porosimetry (MIP) method, water isothermal adsorption experiment and surface scanning test. The influence of supplementary materials on porosity, characteristic pore diameter, pore size distribution and pore fractal dimension was studied. Furthermore, the gas permeability at different water saturation (W100, W80, W60, W40, W20 and W0) was also measured, then intragroup and intra-group error was analysed. With the use of parallel bundle model, the study quantified the contribution of intrinsic flow, boundary slip flow and Knudsen flow to apparent gas permeability. In the quantification process, the intrinsic permeability values kept agreement with the test ones and the pore size distribution was characterized by multi-peak gaussian distribution.The results showed that: (1) Under the non-steady state, the difference in simulation result and actual case of the gas equilibrium process gradually increased with the improvement of saturation degree; (2) The error of intragroup is larger than that of intro-group. At dry state, intra-group error could be controlled within 30% and intro-group 10%. But the former became greater with the increase of pore saturation, and the latter was still not obvious; (3) Compared with experimental values, the error of parallel bundle model calculation was within 10% for material at dry state and 20% at wetting state; (4) The research derived moisture film and gaseous pore distribution curves of wetting materials by taking critical pore diameter and film thickness into consideration, and tortuosity amplification factor expressions was also established.
