胶州湾海底隧道衬砌混凝土的环境条件与耐久性

 隧道的衬砌混凝土一侧接触水或含水土，另一侧接触空气，是典型的干湿交替环境。青岛近年的月平均相对湿度为62%～86%，在正常通车和排风条件下，隧道中或洞口处的CO2浓度为大气中的5倍以上，混凝土易碳化从而导致钢筋锈蚀。海水及地下水中含 ，K+，Na+等，易导致混凝土硫酸盐腐蚀和碱骨料反应破坏。因此，在该隧道衬砌混凝土的耐久性设计中需考虑碱骨料反应、Cl－侵蚀、硫酸盐腐蚀、碳化、冻融、软水腐蚀、高压渗水、积水、火灾等因素；在混凝土的原材料选择、质量控制、配合比及有关性能指标确定、构造措施、施工质量保障及验收标准等方面应严格把关；此外还应考虑表面防水处理、预埋耐久性监测系统等耐久性附加措施。耐久性试验研究表明：混凝土的碳化深度随强度增加而下降；增加胶凝材料中的水泥用量、降低水胶比则有利于提高混凝土抗碳化性能。混凝土Cl－扩散系数与抗压强度成指数函数关系，当隧道混凝土强度等级高于C50，其Cl－扩散系数可小于4×10－12 m2/s。

ENVIRONMENTAL CONDITION AND DURABILITY OF LINING CONCRETE IN KIAOCHOW BAY SUBSEA TUNNEL

The Kiaochow Bay subsea tunnel locates at Kulong Mountain between Tuandao in Shinan District and Xuejia Island in Huangdao District. The area where the tunnel entrance lies is surrounded by large area of seawater. The content of chloride ion in the air near the air-inlet and the entrance of the tunnel is high. Therefore，the areas where the air-inlet and the entrance of the tunnel stand belong to the severe salt mist areas. The monthly average temperature in Qingdao recently is 0 ℃–24 ℃. There are about 90 days in a year when the lowest temperature is below zero. So the lining concrete close to the exits will suffer freeze-thaw cycles. The lining concrete in the tunnel tends to be fractured due to wet-dry cycles. The monthly average relative humidity in Qingdao is between 62% and 86%. So the concrete carbonation takes place faster. Under common transportation and ventilation conditions，the content of CO2 in the air in the tunnel or close to the exits is at least five times of that in atmosphere，where concrete carbonation needs to be considered. ，K+ and Na+ in seawater or underground water can lead to concrete sulphate corrosion and alkali-aggregate action. Therefore，alkali-aggregate action，chloride ion penetration，sulphate corrosion，carbonation，freeze-thaw，fire，and so on should be taken into occount in the durability design of the tunnel lining concrete. It should be stricted on the raw materials of concrete，mixture，properties，quality control，structure design，workmanship，and inspection standards. Furthermore，as the tunnel is an emportant project with 100 years service life，other measures such as concrete surface treatment and imbedded durability monitoring system should be considered. Experiment results show that the carbonation depth of concrete decreases with its increasing compressive strength；and the carbonation resistance capacity of concrete improves with increasing of cement amount and decreasing of w/b. Relationship between chloride ion diffusion coefficient and compressive strength is accordance with exponential function；and the chloride ion diffusion coefficient of concrete would be less than 4×10－12 m2/s when the concrete strength grade is higher than C50.