The prestressed concrete cylinder pipe (PCCP) suffers from cracks and degrades due to the prestress loss which is induced by wire breakage. Reinforcement with external prestressed strands is an option to return the deteriorating pipe’s ability to withstand internal pressures. This reinforcement contributes to actively compensating for the prestress loss caused by broken wires at an economic price. The crack propagation in the core is constrained by the strands. Moreover, the high tensile strength of strands does not decrease with an increase in the bending angle. It is also unnecessary to dewater the pipes during construction. To evaluate the reinforcement effect, a prototype test of a PCCP was performed in an assembled apparatus. The apparatus was mainly constituted by two PCCPs whose internal diameter is 2000 mm. The status of each component of the pipe was measured by resistance strain gauges in three sections along the axial direction at inverted (360°), crown (180°), and spring-line (90°, 270°) orientations. The maximum width of the cracks in the outer concrete core at spring-line reduced from 1.2 to 0.1 mm after strengthening. The cracks of the core concrete changed slightly when the internal water pressure increased to the design pressure of 0.9 MPa. The strengthened pipe was capable of sustaining the design internal water pressure and the water tightness property was in a good state. The strains of the steel strands were all below the tensile strain level. The reinforcement of the PCCP with external prestressed steel strands is able to meet the strengthen requirement of the test.

Prestressed concrete cylinder pipes (PCCPs) can suffer from prestress loss caused by wire-breakage, leading to a reduction in load-carrying capacity or a rupture accident. Reinforcement of PCCPs with external prestressed steel strands is an effective way to enhance a deteriorating pipe’s ability to withstand the design load. One of the principal advantages of this reinforcement is that there is no need to drain the pipeline. A theoretical derivation is performed, and this tentative design method could be used to determine the area of prestressed steel strands and the corresponding center spacing in terms of prestress loss. The prestress losses of strands are refined and the normal stress between the strands and the pipe wall are assumed to be distributed as a trigonometric function instead of uniformly. This derivation configures the prestress of steel strands to meet the requirements of ultimate limit states, serviceability limit states, and quasi-permanent limit states, considering the tensile strength of the concrete core and the mortar coating, respectively. This theory was applied to the reinforcement design of a PCCP with broken wires (with a diameter of 2000 mm), and a prototype test is carried out to verify the effect of the reinforcement. The load-carrying capacity of the deteriorating PCCPs after reinforcement reached that of the original design level. The research presented in this paper could provide technical recommendations for the application of the reinforcement of PCCPs with external prestressed steel strands.

Two years after the Zhanghewan Pumped-Storage Power Station was put into operation, more than 500 blisters appeared in the asphalt concrete facing of the upper reservoir, and nearly half of them ruptured at the surface. The blistering mechanism of the asphalt concrete facing was studied in this paper. Through on-site inspection and coring inspection, it was found that the blistering was caused by the vapor pressure formed by the water enclosed in the middle of the impervious layer during high temperatures. Numerical analysis showed that the temperature 5 cm below the surface could reach 50–60 °C. Through numerical analysis and model tests, the internal water at this temperature may form a vapor pressure of 20 kPa. Finally, the blister size of the asphalt concrete facing at this temperature and pressure was studied with a model test. The possible sources of moisture inside the impervious layer were also analyzed through a core test, which found that moisture was most likely to be introduced by water spraying during rolling.

In cold regions, concrete is inevitably subjected to freeze–thaw (F–T) damage, where repeated water–ice phase transitions progressively erode its microstructure and shorten its service life. Compared with the abundant research focusing on macroscopic performance degradation, systematic summaries addressing the microstructural evolution of pores, cracks, and the interfacial transition zone (ITZ), as well as corresponding prevention measures, remain limited. This paper reviews studies from 2013 to 2025, outlining key deterioration mechanisms under F–T action, including pore coarsening, ITZ weakening, and microcrack propagation. Four frost resistance enhancement strategies are compared: introducing stable microbubbles, refining the pore structure with pozzolanic or nano admixtures, bridging cracks with fibers, and applying hydrophobic treatments to block water ingress. The findings indicate that combining multiple measures yields superior frost resistance. By integrating microstructural observations with engineering improvement approaches, this review provides a holistic perspective for the design of durable concrete in cold regions and highlights the need for further research on multi-factor coupling mechanisms, optimization of composite admixture systems, and the functional mechanisms of novel nanomaterials.

Modeling complex conditions involving extensive engineering structures with large numbers of beams and columns often requires a mixture of analytical modeling based on beam theory and numerical simulations involving finite element models composed of solid or shell elements. However, high levels of deformation in the planar configuration of cross-sections arising under extreme external loads, such as intensive earthquakes, explosions, and hurricanes, greatly complicates the task of fitting the numerical simulation results to the planar cross-sections required by beam theory. The present work addresses this issue by proposing a fitting method based on a least squares approximation method. The fitting problem is first transformed into a process of solving a cubic equation whose coefficients are integrals over the simulated cross-section. The solution of the cubic equation is defined using explicit formulae developed for calculating the integrals over the surfaces of single solid or shell elements lying within the cross-section by combining the shape functions and degree of freedom results of the elements. The proposed fitting method is then applied for analyzing the blast resistance of steel structures. The potential application of the proposed method is demonstrated by evaluating the rotations, shear deformations, and moment–curvature relationships of the fitted cross-sections.