Concrete-face slabs are the primary anti-permeability structures of the concrete-face rockfill dam (CFRD), and the resistance of face slab concrete to permeability is the key factor affecting the operation and safety of CFRDs. Herein, the influences of five fly ash dosages (namely 10%, 20%, 30%, 40% and 50%) on the permeability property of face slab concretes were investigated. Moreover, the difference in the permeability caused by the fly ash dosage variations is revealed in terms of the pore structure and fractal theory. The results illustrate that: (1) The inclusion of 10–50% fly ash lowered the compressive strength of face slab concretes before 28 days of hydration, whereas it contributed to the 180-day strength increment. (2) The incorporation of 10–50% fly ash raised the average water-seepage height (D_m) and the relative permeability coefficient (K_r) of the face slab concrete by about 14–81% and 30–226% at 28 days, respectively. At 180 days, the addition of fly ash improved the 180-day impermeability by less than 30%. (3) The permeability of face slab concretes is closely correlated with their pore structures and D_s. (4) The optimal fly ash dosage in terms of the long-term impermeability and pore refinement of face slab concretes is around 30%. Nevertheless, face slab concretes containing a high dosage of fly ash must be cured for a relatively long period before they can withstand high water pressure.

The conventional methods used to analyze the shear lag effect in simply supported box girders assume that the neutral axis of the section coincides with the centroid, which does not strictly satisfy the axial equilibrium condition. To address this problem, this study proposes an analysis method in which three independent functions for the shear lag are employed to define the different shear lag strengths of the top slab, the bottom slab, and the cantilever slab. To fulfill the axial equilibrium condition of the box girder and to automatically locate the neutral axis position, the longitudinal displacement of the web is introduced. The shear deformation of the box girder is also considered. The governing differential equations and corresponding boundary conditions for displacement variables such as deflection and rotation of the box girder are derived through the application of the principle of virtual work. The differential equations are solved by utilizing the boundary conditions to obtain the analytical expressions of the shear lag function, longitudinal displacement of the web, rotation, deflection, and neutral axis position. Furthermore, after performing the finite element analysis, the effectiveness of the proposed method is verified by comparing the results with those obtained from conventional methods and finite element analysis. Furthermore, the influence of the axial equilibrium condition is quantified on axial force and stress difference ratios under three methods. Finally, extensive parametric analysis is carried out to investigate the effect of different parameter ratios on the ratios of the stress difference of the flanges. The results show that when the axial equilibrium condition is not considered, the axial stresses in the upper flange of the simply supported box girder are underestimated, especially at the intersection of the top, cantilever slab, and web, and the axial stresses in the lower flange are overestimated. As a result, the method in this study is able to calculate the axial stresses and deflections on simply supported box girders more accurately.

Hydraulic engineering projects in high-altitude environments are subject to significant diurnal temperature variations, necessitating concrete with high freeze–thaw resistance. Aggregates play a crucial role in the freeze–thaw durability of concrete. However, the impact of different parent rock types on concrete’s freeze–thaw resistance remains underexplored. This study investigated the effect of five common coarse aggregate types—granite (Gr), tuff (Tu), sandstone (Sa), limestone (Li), and pebble (Pe)—on the freeze–thaw resistance of dam concrete subjected to freeze–thaw cycles. The relationship between the rock type’s properties and the degradation patterns of concrete with different aggregates under freeze–thaw conditions was analyzed. Additionally, the damage mechanisms at the paste–aggregate interface were explored using SEM-EDS, pore structure analysis, and nano-indentation, along with the characteristics of the hydration products in the transition zone. The results showed that the aggregate type significantly influences freeze–thaw resistance, with Gr performing best (Gr > Li > Pe > Tu > Sa), correlating with pore structure and pore spacing. Gr, due to its superior freeze–thaw resistance, was optimal for regions with stringent freeze–thaw conditions. Although the interface zone exhibited a lower elastic modulus and hardness compared to the paste region due to a lower total amount of hydration products, these differences did not substantially affect the freeze–thaw performance of the concrete. This study, contributing to the expansion of the existing knowledge base on the effects of aggregate types on freeze–thaw resistance, provided valuable engineering insights for the selection of coarse aggregates in hydraulic concrete applications in high-altitude regions.

To characterize the material state and residual reactivity of long-service dam concrete, concrete cores extracted from the Lushui Reservoir Dam after more than 60 years of service were investigated. Their long-term macroscopic properties were evaluated, and the hydration products and microstructural features of the aged binder were characterized using X-ray diffraction, thermogravimetric analysis, scanning electron microscopy/energy-dispersive spectroscopy, and mercury intrusion porosimetry. The residual hydration capacity of the aged binder was further assessed through hydration heat and mortar strength tests. The results showed that the compressive strength of the concrete cores was mainly distributed within the range of 20–40 MPa, while the splitting tensile strength was mainly distributed within the range of 1–3 MPa, indicating that the concrete still retained relatively good basic mechanical properties after more than 60 years of service. The resistance to chloride ion penetration was generally favorable, whereas the frost resistance was relatively poor. The aged binder still contained identifiable Ca(OH)₂, AFt, C-S-H, and CaCO₃, and the local binder skeleton and aggregate–paste interface remained relatively stable. The residual hydration capacity of the aged binder was approximately 14–17%, indicating that the binder system had not become completely inert and still retained measurable residual reactivity. These findings provide a useful reference for evaluating the material state of long-service hydraulic concrete.