试样尺寸对水蒸气扩散系数瞬态测试的影响

为了分析试样尺寸对水蒸气有效扩散系数瞬态测试结果的影响，利用瞬态法测试底面积为50 mm×50 mm，长度分别为120、150、200、250 mm的4种B04级加气混凝土试样沿长度方向的水蒸气有效扩散系数，比较实验结果与采用标准稳态法的测试结果.结果表明，随着试样尺寸的增长，水蒸气有效扩散系数的瞬态测试值逐渐降低.长度为120 mm试样的瞬态测试值略高于稳态测试值，相对湿度高于50%时的最大偏差不超过10%，耗时为24 h；长度为150 mm试样的瞬态测试值与稳态测试值在整体上最为接近，在整个相对湿度区间的最大偏差不超过13%，测试耗时为36 h；长度为200、250 mm试样的瞬态测试值比稳态测试值显著偏低，最大偏差超过25%，耗时均超过60 h.根据测试结果，建议采用长度约为150 mm的试样对该型加气混凝土的水蒸气扩散系数进行瞬态测试.

Effect of sample size on transient measurement of water vapor diffusion coefficient

The transient experiments of water vapor diffusion coefficient in the lengthwise direction of B04 autoclave aerated concrete (AAC) samples were performed to reveal the effect of sample size on transient measurement of water vapor diffusion coefficient. The axial sample lengths were 120, 150, 200 and 250 mm, respectively, while maintaining a constant cross-sectional area of 50 mm×50 mm. Results of steady-state and transient measurements were compared. Results showed that the transient results increased along with the decrease of the samples' length. The transient results of the 120 mm sample were slightly higher than the steady-state measurements while the maximum deviation was less than 10% when the relative humidity was higher than 50%, and the measurement time was 24 h. The transient results of the 150 mm sample had the best agreement with the steady-state results with an overall deviation of less than 13%, and the measurement time was 36 h. The transient results of 200 mm and 250 mm samples were apparently lower than the steady-state results, while the maximum deviation was greater than 25%, and the measurement time was longer than 60 h. According to the results, the sample length of 150 mm is recommended for the transient measurements on the water vapor diffusion coefficient of this type of AAC.