高速水流下空蚀热效应对水泥水化产物的破坏

Thermal Effect on the Failure of Cement Hydration Products Under High Velocity Flow Cavitation

随着坝工技术的提高和水力资源的深入开发利用,高坝建设发展迅速,其泄量大、流速高时的泄洪消能和抗空蚀保护问题是目前建设中的主要技术难题。区别于传统对高速水流引发空蚀的力学破坏定义,本研究从热学角度阐述了空蚀引起破坏的机理。本研究利用超声波空蚀仪进行不同类型水泥净浆空蚀试验,综合空蚀破坏面表面分析和对空蚀破坏后的水泥水化产物微观成分分析,对空蚀在硬化水泥表面产生的热效应进行测定和研究分析,初步讨论空蚀热效应对混凝土结构的破坏机理。试验结果表明,空蚀对水泥净浆表面的破坏不仅是简单的力学破坏,同时空蚀热效应还可以造成水泥水化产物的部分分解。具体而言,经过6h超声空蚀试验后的试样,水化凝胶损失量不低于40%,氢氧化钙的损失量在25%以上,这对硬化水泥浆体的劣化有较为显著的影响。

With the development of dam construction skills and further utilization of water power resources,the construction of high dams improves rapidly.It leads to a major problem of protection against the cavitation erosion caused by high velocity and large flow of flood discharge.Instead of the conventional way of mechanical analysis on cavitation,this paper was devoted to illustrate the thermal impact on the kind of erosion.Ultrasonic cavitation device was utilized for the test of various kinds of cement paste,with a combination analysis of erosion surface of hardened cement paste and micro-analysis of hydration product,the article studied the thermal effect of cavitation on the surface of hardened cement paste.The thermal effect of cavitation erosion on cement hydration products was initially discussed in this paper.Results indicated that cavitation erosion on cement paste is not only a simply mechanical failure but also conducts a thermal decomposition on hydration of cement,which could cause the partial decomposition of cement hydration products.To be specific,the mass loss of hydration gel substances is no less than40%so as the loss of hydrated lime is more than25%during a6hours ultrasonic cavitation experiment.In that way,the considerable hydration mass loss could lead to a significant impact on cement paste deterioration.