采用RapidAir图像分析仪测试硬化混凝土气孔结构时的影响因素

Error Analysis of Measurement of Air-void System of Concrete using RapidAir Image Analyzer

气孔结构是混凝土抗冻性能的重要指标之一,然而采用图像分析仪法测试硬化混凝土气孔结构的结果与传统的人工显微镜法有一定的偏差,以Rapid Air图像分析仪为例,系统地讨论了采用RapidAir测试硬化混凝土气孔结构时的影响因素:导线分布差异、导线长度、阈值、制样和焦距。指出采用自动图像分析仪测试硬化混凝土气孔结构参数时,应延长导线长度以减小导线分布差异造成的误差,当导线长度从ASTM C457等相关规范要求的2 600 mm增加到3 100 mm时,含气量和气泡间距系数的最大相对误差分别从6.5%和9.6%减小2.9%和4.9%;按照目测设定的阈值和焦距造成的误差很小,可以忽略;制样时,采用自动研磨机比手工方式研磨平面对水泥浆体损伤小,采用硫酸钡干粉填充试样表面的气孔可获得更好的黑白对比度,比氧化锌浆体的效果好。

In order to fully utilize the advantage of the automatic image analyzer Rapid Air for the measurement of the air void structure of hardened concretes, main factors relevant with the use of RapidAir were investigated,including the traverse line distribution and length, the threshold level, sample preparation and focus. The test results show that the error caused by different traverse line distribution can be minimized by increasing the traverse line length. Thus,for higher precision, the traverse line length should be longer than that specified by ASTM C 457 in the RapidAir testing; the errors caused by setting the threshold level and focus by naked eyes are negligible. The hardened paste at the sample surface are less damaged by using automatic grinding machine than by manual grinding. Filling void with dry barium sulfate powder produces a better image contrast than filling with zinc oxide paste.