Durability Test And Assessment Of Concrete Structures In Hong Kong-zhuhai-macau Bridge

This study investigates the quality of concrete based on the durability design of the Hong Kong-Zhuhai-Macao sea link project, and then performs the durability assessment and redesign of all structural concrete members of the HZM Bridge. This work provides data support for construction quality control and acceptance as well as service life management.First of all, the compressive strength and chloride diffusion coefficient obtained from laboratory, along with the covercrete thickness, air permeability and electrical resistance obtained from in-situ through non-destructive tests,are summarized and analyzed. The results show that both the compressive strength and chloride diffusion coefficient of the immersed tube tunnel achieve the expected construction quality. The relatively low air permeability indicates that structural concrete of tunnel has high compactness. The electrical resistance obeys normal distribution and is correlated strongly with the hardening age. It can be found that the air permeability and electrical resistance are qualitatively inversely correlated.Then the durability risk is assessed for chloride penetration based on the acquired data during construction phase. The assessment model for the chloride ingression is reviewed, and the parameters of the model along with their statistical features are discussed. The additional protective measures are also taken into consideration in the model. The reliability index of 120 years is got through Monte-Carlo method. The results show that the structural members in atmospheric zone and immerged zone own relatively high reliability index and therefore can be exempted from maintenanc; The failure probability of most structural members in splashing zone is between 1-5%,thus durability maintenance planing is needed; The internal side of the buried toll bridges, C ramp bridge and immerged tube tunnel could reach high failure probability(above 10%) in case of sea water infiltration. For this reason, it’s important to monitor the water infiltration of these structural members during construction, and the corresponding reassessment and redesign are also needed.Cathodic protection mearsures of the tube tunnel are needed in case of water infiltration, and the startup time can be determined according to the waterinfiltration intensity and maintenance level.Then the principle and method of durability redesign through life cycle costing(LCC) method are discussed, and the durability maintenance plans of the tube tunnel and the buried toll bridges in splashing zone are shown as durability redesign examples. The relation between the startup time of cathodic protection and the water infiltration intensity under different maintenance levels is obtained through calculation. The time-dependent curves of failure probability and the reliability index of the buried toll bridges are updated based on a group of simulated exposure data, then the Level-2maintenance plan is chose after comparison through LCC method.