Due to low activity or long mineralization time, traditional mineral agents for self-healing concrete generally need a long time to achieve a desired repair efficiency. Inspired by epoxy resin AB glue which can consolidate in a short time when mixing the two components together, a novel type of fast-responsive capsules based on two soluble components was designed for self-healing concrete. Component A (sodium carbonate) and component B (calcium acetate) were encapsulated in two different groups of capsules, respectively, coated with three layers consisting of epoxy resin and fine sands to achieve superior waterproof and alkali resistance properties. After rupture of the capsules, the rapid response with respect to core material dissolution and precipitation can be realized in presence of water, by which the cracks below 200 μm can be healed in 3 days. Super absorbent resin (SAP) embedded in the capsules could expand in contact with water, and further improve the self-healing efficiency of the capsules by blocking the crack.

Cutter suction dredger is one of the ship types widely used in dredging engineering, especially for rock dredging, this ship type has more obvious advantages. Compared with dredging of sediment, rock excavation requires higher performance of cutterhead. Therefore, the determination of cutting force and the research of excavation effect in the process of cutting rock with cutter teeth have important guiding significance for the design of cutterhead and dredging construction. In view of the heterogeneity of natural rock material, complex internal mechanical properties and poor regularity and repeatability of tests, concrete samples were innovatively prepared to replace natural rock samples. A large scale model test platform was used to test the linear cutting of rock by cutter teeth. The cutting resistance of cutter teeth and the groove shape of the rock sample under different cutting angles and cutting depths were compared and analyzed. The test results show that in the process of rock cutting, cutting resistance of cutter teeth varied linearly with cutting depth, but the regularity was not obvious when cutting depth was small. The dimensionless cutting specific energy (SEQ) decreased with the increase of cutting depth, and it decreased rapidly when the cutting depth was small; when the cutting depth reached a certain value, SEQ basically did not change. The cutting width increased with the increase of cutting depth while they were linearly correlated, and the fitting curves under different cutting angles were basically the same.

Operation and maintenance (O&M) costs account for a large proportion of the total costs for offshore wind energy. Performing a reasonable maintenance strategy is an effective approach to reduce O&M costs and gain more profits. In this paper, an opportunistic maintenance strategy for offshore wind turbine systems considering maintenance intervals of each subsystem is proposed to minimize the total maintenance cost. First, a Non-homogeneous Continuous-Time Markov Process based state transition model is established to study degradation process of subsystems. The influence of maintenance time schedule on the maintenance cost is studied to obtain the optimal maintenance intervals of each subsystems. Then, an opportunistic maintenance model considering economic dependencies between multiple subsystems is proposed to optimize the maintenance strategy by combining maintenance activities of individual subsystems to a grouping maintenance activity. A numerical example is used to indicate the significant effectiveness of the maintenance model. The result shows that the total maintenance cost of an offshore wind turbine system will be reduced by adopting the opportunistic maintenance strategy when compared with conventional preventive maintenance strategy.