膨胀土水泥改性掺灰量测定的龄期效应研究

南水北调中线工程采用水泥改性的方法对膨胀土进行改良,而水泥掺量是决定膨胀土改性质量的重要指标,因此确保掺灰量检测的准确性尤为关键,而采用EDTA(乙二胺四乙酸二钠)滴定法测定水泥掺量时存在龄期效应。为了研究水泥改性土龄期对EDTA二钠滴定结果的影响,讨论该法在南水北调中线工程膨胀土地区水泥改性土掺灰量检测中应注意的问题及解决方案,选取了南阳地区中膨胀土放置不同时间后进行EDTA滴定检测。试验结果表明龄期大于2h且目标掺灰量大于4%时,水泥改性土有效钙量明显衰减,EDTA滴定法检测结果将小于实际水泥掺量,此时需用对应时间的EDTA二钠消耗标定曲线测定或用该土样有效钙量衰减曲线校正滴定结果,以确保检测结论的准确性。

Age Effects on EDTA Titration in Detecting Cement Content for Treatment of Expansive Soil

In the Middle Route of the South-to-North Water Transfers Project,cement is used to modify the engineering characteristics of expansive soil,and the quality of the stabilized expansive soil depends on the cement content,therefore it is important to ensure the accuracy of detecting the cement content.EDTA(Ethylene Diamine Tetra Acetic Acid Disodium Salt) titration method is used to detect the cement content;however,age effects occur using this method.In this paper,expansive soil samples obtained from Nanyang area were mixed with different cement contents and then titrated using the EDTA method after they were stored for different time periods,which can help understand the age effects of the stabilized soil on the EDTA titration in detecting the cement content.The problems and solutions of using the EDTA titration method in detecting the cement content of the stabilized expansive soil in the Middle Route of the South-to-North Water Diversion Project were discussed.The experiment results showed that the effective calcium content decreases significantly and the detected cement content using the EDTA titration method may be lower than the actual value when the storage time is longer than 2h and the cement content is not less than 4%.In this case,the standard curve of EDTA consumption with time or the decay curve of the effective calcium content should be used to correct the detected value to ensure the accuracy of the conclusions.