Chemical and mineralogical alterations of concrete subjected to chemical attacks in complex underground tunnel environments during 20-36 years

This paper investigates the chemical and mineralogical alterations of concrete in underground tunnel structures built from 1980 to 1996, located on the China's east seashore. The underground water around the tunnels had once been treated to be not or little aggressive. However, the complex environments in the tunnels had increased the aggressiveness of certain ingredients, thus causing chemical attacks. The chlorides in the leakage underground water cause chloride attack, and the NaCl crystallizations on the surface of the C50 pre-cast concrete segments induce a deeper chloride contamination. When the concrete suffers flowing leakage water, calcium leaching also occurs, leading to decalcification and magnesium incorporation. Under this circumstance, C50 pre-cast concrete shows a higher resistance compared with 00 cast-in-place concrete, mainly due to the low water to binder ratio. Within the C30 cast-in-place concrete facing concentrated leakage water and NaCI crystallizations, a strong magnesium chloride attack is observed. Besides the materials factors, the environmental factors, including the high concentrations of both chloride and magnesium ions, the removal timing of calcium ion, and the water saturation, are believed to take responsibility for the magnesium chloride attack. (C) 2017 Elsevier Ltd. All rights reserved.

本文研究了位于中国东部沿海1980年至1996年建造的地下隧道结构中混凝土的化学和矿物学变化。隧道周围的地下水曾经被处理为无侵蚀性或侵蚀性很小。然而，隧道内的复杂环境增加了某些成分的侵蚀性，从而导致化学侵蚀。渗漏地下水中的氯化物导致氯离子侵蚀，C50预制混凝土管片表面的氯化钠结晶导致更深入的氯离子污染。当混凝土遭受流动的渗漏水时，还会发生钙溶出，导致脱钙和镁掺入。在这种情况下，C50预制混凝土与现浇混凝土相比表现出更高的抗性，这主要是由于其水胶比低。在面临集中渗漏水和氯化钠结晶的C30现浇混凝土中，观察到强烈的氯化镁侵蚀。除了材料因素外，环境因素，包括高浓度的氯离子和镁离子、钙离子的去除时间以及水饱和度，被认为是氯化镁侵蚀的原因。（C）2017爱思唯尔有限公司。保留所有权利。