Abstract: At present, the conventional method for the determination of concrete carbonation depth is the phenolphthalein alcohol method (using 1wt% phenolphthalein alcohol solution as an indicator). However, it can only determine the fully carbonated zone with the pH value of less than 10. The partially carbonated zone (PCZ) lies between the fully carbonated zone (FCZ) and the non-carbonated zone (NCZ). In the PCZ, the pH value of the concrete pore solution decrease due to carbonation.Instability of the steel bar's passivation film will arise when the pH value is down to 11.5, affecting the concrete structure's service life in the future. Unfortunately, the conventional phenolphthalein alcohol method can not detect this important zone and thus can not reflect the concrete's real carbonation damage. This work explored a method to determine the concrete carbonation depth by testing the pH values of layer-by-layer grinding concrete powder. The width of FCZ and PCZ in concrete carbonated for 7 d, 14 d, 28 d, and 56 d was measured. The Ca(OH)2 and CaCO3 profiles of carbonated concrete were measured by thermogravimetric analysis (TG). The relationship between Ca(OH)2 content and pH value was established. Results show that the pH value method's carbonation depth is 1.5—2 times that of the phenolphthalein alcohol method. Part of the PCZ, where the steel bar's passivation film has been instable, is ignored when the phenolphthalein alcohol method is used to determine the carbonation depth. The pH value method is more accurate in measuring the real carbonation depth of concrete. The pH value is positively correlated with the Ca(OH)2 content in each concrete layer, while it is negative collated with the CaCO3 content in each concrete layer. Therefore,the pH profile can reflect the carbonation reaction progress in concrete. This research provides more accurate carbonation depth data for predicting the carbonated concrete structure's service life.
张铖, 王玲, 姚燕, 史鑫宇. 逐层磨粉pH值法测定混凝土碳化深度的试验研究[J]. 材料导报, 2022, 36(7): 21030009-4.
ZHANG Cheng, WANG Ling, YAO Yan, SHI Xinyu. Determination of Concrete Carbonation Depth by Testing the pH Value of Layer-by-layer Grinding Concrete Samples. Materials Reports, 2022, 36(7): 21030009-4.
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2022, Vol. 36 
