To investigate the maintenance effect of diaphragm-to-rib fatigue cracks via steel plate reinforcement, finite element models of different-shaped steel plates were established. Stress intensity factors at the crack tip before and after reinforcement were obtained, and the variations in stresses were studied. Polygonal steel plate reinforcements were then carried out on a real bridge based on the finite element calculation results. The changes in stress amplitudes and fatigue damage degrees at the crack tip were analyzed via the rain-flow counting method and Miner’s linear damage accumulating theory. The results show that both the polygonal steel plate and the rectangular steel plate could effectively eliminate the stress concentration and restrain the propagation of cracks. The stresses in other parts of the arc notch increased after reinforcement and polygonal steel plates had less influence. After the reinforcement in a real bridge, the cycle number of high stress amplitudes at the crack tip decreased significantly. The fatigue damage degree of the repaired part reduced by 70.1%, which verified the maintenance effect via polygonal steel plate reinforcement on diaphragm-to-rib fatigue cracks.

Borehole packer testing is a commonly used method to obtain the in-situ permeability coefficients, which are closer to the actual subsurface conditions compared to indoor tests. Current methods for determining permeability coefficients through borehole packer testing are limited to semi-infinite spaces like rock masses, failing to accurately describe the permeability coefficient of domains with different shapes, such as waterproof curtains, thus leading to evaluation errors. This study proposed a novel approach that utilizes borehole packer tests on waterproof curtains for determination of in-situ permeability coefficients. Based on the assumption that seepage within the waterproof curtain obeys Darcy's law, and following the borehole packer testing procedures, the method derives specific formulas for different cross-sectional shapes of waterproof curtain, experimental parameters and groundwater levels. Applying this method to calculate domains with actual shapes has higher permeability coefficient values compared to the previous semi-infinite domain methods, which had underestimated the permeability coefficients of waterproof curtains. The study presents a calculation model for borehole packer tests on waterproof curtains under various geological formations and conditions, providing a more accurate approach to determine the in-situ permeability coefficients.

Recycled concrete powder (RCP) collected from waste concrete recycling presents significant variation in both composition and hydration behavior, while available literatures were mainly carried out on RCPs derived from target concrete, mortar, or cement paste, RCPs collected from actual waste concrete is totally different from RCPs reported, their roles has not been clarified yet due to its complexity in components, leading to substantial deviation in understanding the roles of RCP in cement-based materials. In this study, RCP collected from a waste concrete reutilization plant was classified into five fractions, then effects of RCP fractions on heat evolution and mechanical properties of cement pastes were investigated. The results showed that hydration products and un-hydrated clinker were predominantly concentrated in fine RCP fraction, while higher proportion of aggregate grains (mainly quartz, anorthite, and dolomite) in coarse RCP fraction, indicating that cement paste was pulverized or milled into finer particles prior to fine and coarse aggregates due to its diminished elastic modulus. Compared with coarse RCP fraction, fine RCP fraction showed significant acceleration of cement hydration and higher strength contribution, which can be attributed to the remarkable pore refinement of fine particle and conspicuous seeding effect of C–S–H in RCP. Furthermore, increased dissolution of Si4+ and Al3+ from the fine RCP fraction was observed, then more hydration products were generated to densify the microstructure of cement paste. The results provided a deeper insight into the roles of RCP in cement-based materials, and then facilitate the efficient utilization of RCP to achieve resource-conservation development.

Abstract This paper studies the spatial distribution of the corrosion products in concrete based on a series of experimental investigations of a marine construction. The distributions of defects and corrosion products in the concrete cover were identified in a mesoscale based on the computed tomography test, and the fractal dimension of cracks was analyzed. Some cracks and defects were filled by corrosion products in various degrees. The results showed that the defects were significantly influenced by the shape and relative location of the deformed steel reinforcement, which would then lead to the variation of the corrosion layer. The migration of corrosion products was particularly affected by the location and geometry of the defects, which could provide a suitable channel for the migration of corrosion products. The research can be helpful for the prediction of concrete cracking performance induced by the chloride-induced corrosion of the steel reinforcement.

Ultrafine grinding is expected to be an effective method to increase the pozzolanic activity of RBP, since RBP has superior grindability. The aim of this paper was to investigate the effects of 30 % ultrafine RBP with particle size of 8.6 μm, 4.5 μm, 3.6 μm and 2.7 μm on the fundamental properties, hydration kinetics and microstructure evolution of blended cement. The setting times, water requirement for normal consistency, rheological properties, hydration heat, hydration degree, mechanical strength and pore structure of cementitious material were evaluated. Results show that when 30 % RBP was added, the water requirement and viscosity of blended cement increased significantly with the decrease of RBP particle size, while the setting time was shortened due to the acceleration of early-age cement hydration. The parameters for the Boundary Nucleation and Growth (BNG) model indicate that the nucleation and growth rates of hydration products increased by 1.43 times and 1.27 times when RBP with D50 = 2.7 μm was added, thus the cement hydration degree reached more than 50 % in the first 72 h. Based on the thermogravimetric analysis (TGA), the pozzolanic reaction degree of ultrafine RBPs was more than 15 %–25 % depending on its size, and the hydration degree of cement in RBP-PC pastes was more than 80 %. As a result, blended cement mortars with up to 30 % ultrafine RBPs has slight or even no strength loss after curing for 90 days, as RBP-PC paste has a denser microstructure.

Lithium silicate (LS) crack repairing material, working as a crystal waterproof material, could be used to strengthen concrete made from solid waste materials. This paper presents the results of water absorption and rapid freeze–thaw tests with concrete specimens coated with LS. Concrete specimens with different water–binder ratios and air content (0.35–1 and 0.55–4.5) were tested. The moisture uptake and water absorption coefficient were analyzed in the water absorption test. The water absorption coefficient of LS-coated specimens was lower than that of uncoated specimens, resulting in a lower total moisture content. The relative dynamic modulus of elasticity was calculated by the fundamental transverse frequency (Er) and ultrasonic velocity (Ev), respectively. Er and Ev exhibited similar attenuation characteristics, and the attenuation of LS-coated specimens was lower than that of uncoated specimens. A two-segment freeze–thaw damage model based on Er and Ev was employed to predict the service life of concrete. The relative errors of the service life results calculated by Er and Ev were within 10%. The two-segment freeze–thaw model could be used for the service life prediction of concrete structures. The present work provides new insight into using LS to improve the service life of concrete.

PurposeThis paper aims to investigate the effect of characteristic parameters of pits on the mechanical properties and fracture model of cable steel wires.Design/methodology/approachThe tensile test and finite element analysis of steel wires with corrosion damage were carried out. The stress development of corroded steel wire under corrosion morphology was studied by the 3D reverse reconstruction technology. The internal relationship between the stress triaxiality, equivalent plastic strain and pit depth, depth-width ratio of corroded steel wire was discussed.FindingsWith the increase of corrosion degree, the neck shrinkage phenomenon of steel wire was not significant, and the crack originated near the pit bottom and expanded to the section inside of specimen. The fiber area of corroded steel wire decreased while the radiation area increased, and the ductile fracture gradually changed to brittle fracture. The pit size significantly changed the triaxial degree and distribution of stress and accelerated the initiation and propagation of internal cracks at the neck shrinkage stage.Originality/valueThe proposed fracture model based on the void growth model could accurately simulate the fracture behavior of steel wires with corrosion damage.

A concrete filled steel tubular (CFST) column internally reinforced with steel stirrups has significantly enhanced fire resistance over a conventional CFST column without stirrups. Resistance to shear may be a vital load case to be considered when designing CFST columns. However, there is comparatively little research into the shearing behaviors of CFST columns and the existing design equations do not adequately describe the contributions of different components to the total shear resistance. In this study, thirty-five square CFST columns, with and without stirrups were fabricated and tested to failure under combined shear load and axial compression. The portions of observed shear resistance contributed by the steel tube, concrete infill and stirrups were isolated. The concrete contained demolished concrete lumps (DCLs). The tube’s thickness, the ratio of shear span to depth, the axial load ratio, the replacement ratio of DCLs, the center-to-center spacing between stirrups, and the gap between steel tube and stirrups were varied in the experiments. The test results showed that: (1) the shear capacity was much greater at a smaller shear span-to-depth ratio, but the ratio had little effect on the contribution of the steel tube to shear resistance when ranging from 0.15 to 0.50; (2) the shear capacity gradually increased as the axial loading increased, but the shear contribution of the steel tube decreased; and (3) the internal stirrups contributed little to the shear resistance, and there was little difference in shear capacity as the gap between the stirrups and tube increased from 15 mm to 35 mm. A method to adequately capture the respective contribution of different components in the column was proposed. The new method generally gave more accurate predictions than the methods currently in use, and its predictions were generally conservative.

Multiple unusual vibrations occurred in SEG Plaza from May 18 to 20, 2021. To investigate the causes of these vibrations, a rigidity compression wind tunnel test was applied to study the wind-induced response of the main structure, and acceleration sensitivity analysis was conducted with parameters such as wind speed, structural period and damping ratio included. Additionally, the mast vortex-induced resonance equivalent force of reaction in the bottom was exerted on the top of the structure to obtain the acceleration response of the main structure with mast. Based on the evaluation of the vibration response of the structure before and after considering the mast as per the current specifications, it is indicated that the base overturning moment of the structure is much smaller than the specification value excluding the factor of mast, and the acceleration response varies significantly with wind pressure, structural frequency and damping ratio, but the centroid acceleration and the angular acceleration meet the comfort requirements. This indicates that the wind load on the main structure is not the dominant cause of the structural vibration. With the mast taken into account, the acceleration response of the structure exceeds the limits of the comfort level to varying degrees. For a mast damping ratio of 0.3%, the maximum angular acceleration exceeds the H-90 limit and the comfort level is poor. These findings provide considerable evidence that the dominant cause of vibration in the SEG Plaza was the vortex resonance of the top mast inducing higher mode resonance in the main structure.