Adding basalt fiber to concrete can improve the mechanical properties of concrete, and it is also one of the best ways to enhance the ultimate bearing capacity of concrete structure. In this paper, the construction performance and the compressive strength of basalt-fiber-reinforced concrete (BFRC) with five kinds of fiber lengths and eight kinds of fiber volume content subjected to an axial load are systematically investigated. The optimum fiber length and fiber volume content are obtained by comprehensively considering the construction performance and compressive strength. Moreover, the prediction model and finite element analysis method of the ultimate bearing capacity of basalt-fiber-reinforced concrete are developed. The results show that the optimum fiber length is about 12–24 mm and the fiber volume content is 0.15%. Adding an appropriate amount of basalt fiber can effectively improve the ultimate bearing capacity of concrete short columns, with maximum and average increases of 28% and 24%, respectively. In addition, the comparison with the experimental results shows that both the proposed prediction method and the finite element modeling method have good applicability, and they can be used to predict the ultimate bearing capacity of the BRFC short columns in practical engineering.

The fatigue crack propagation behaviour of Q550E high-performance steel (HPS) is studied in this paper. Static tensile testing and fatigue crack propagation testing were carried out, and the results were compared with those of Q235. Finite element models were developed and verified against the experimental results. The impacts of the initial crack angle, crack depth ratio, stress ratio, thickness, and corrosion pitting on the fatigue crack propagation behaviour of the HPS were analysed. The results show that the fatigue life of Q550 was reduced by 18% due to the corrosion pitting, but it did not change the crack propagation path. When the stress intensity factor is higher than a certain value, the fatigue performance of Q235 is better than that of Q550E. The initial crack angle of 52.5° is the critical angle of the crack stress intensity factor. The steel tends to fracture as the crack depth ratio increases, and more attention should be paid to the effective crack length in engineering practice. An increasing stress ratio leads to a smaller stress intensity factor, and the thickness affects the stress intensity factor in the later stage. The crack stress intensity factor around the corrosion pits gradually decreases along the thickness direction, and the crack tips around the corrosion pits tend to reach the yield state initially, accelerating the fatigue fracture of the specimen and ultimately leading to a decrease in fatigue life.

High performance concrete (HPC) is a kind of concrete with mineral admixtures, which has better resistance ability to chloride ions diffusion than ordinary concrete. In the present study, the authors carried out a chloride ion diffusion experiment for the HPC with fly ash and silica fume. The influence of the water–binder ratio (W/B), binary (Portland cement–Fly ash (PC-FS) and Portland cement–Silica fume (PC-SF) and ternary (Portland cement–Fly ash–Silica fume (PC-FA-SF)) combinations on the concrete compressive strength and chloride ion diffusion was investigated. It was found that the compressive strength of normal concrete and HPC increase with the decrease in the W/B, the ratio of W/B deceasing value to strength increasing value for normal concrete is 0.74, and for the HPC is 0.20, so the influence of the W/B on the concrete strength for normal concrete was obviously more than the HPC. The influence of the contents of the SF or FA on developing the concrete strength was limited. The concrete compressive strength of ternary combination specimens decreases with the increase in FA or SF when the content of the other mineral admixture SF or FA remained unchanged. The ternary combination was more efficient in prohibiting chlorides ingress insider the specimens than the binary combination. The mesoscopic simulation and the tested value of the chloride ion under the same depth was close, the average ratio of simulation value to tested value was 0.91. The aggregate shape and distribution also had a negligible influence on chloride diffusivity in the HPC, but the chloride ion concentration increased with the increase in aggregate size.

In order to study the bond-slip constitutive model between prestressed tendons and concrete, the pull-out tests of single-strand and multi-strands specimens are carried out. The effect of the number of prestressed tendons on the failure mode, slip characteristics and concrete strain of the pull-out specimens are analyzed, and the constitutive models of bond-slip between for single- strand and multi-strand tendons are also proposed. The results show that the bond mechanism between steel strand and concrete is basically similar to that of deformed steel bar, but the slip process of steel strand along the axis direction is accompanied by rotation phenomenon because it is twisted. Moreover, compared with the single-strand prestressed tendon, the average ultimate bond stress of each tendon of the three-strand prestressed tendons decreases by 13.2%. In addition, the calculated result of the pull-out limit load for the single-strand prestressed tendon is only 2% higher than the experimental value, while the corresponding value of three-strand prestressed tendon is only 3.74% lower than the experimental value. This means that the proposed bond-slip models for single- strand and multi-strand tendons have high reliability.

In the present study, 104 sets of flexural tests on corroded prestressed concrete (CPC) beams were gathered from different publications. A flexural strength database for CPC beams was created by incorporating standardized concrete strength and the corrosion rate of prestressed steel. This database enables the analysis of the impact of different factors on the flexural capacity, such as the beam’s width and effective depth, concrete compressive strength, shear span ratio, the prestressed steel’s corrosion level, prestressing ratio (PPR), and the effective prestress. The findings show that the flexural strength of the CPC beams is notably influenced by variations in beam width, shear span ratio, and the prestressed steel’s corrosion level and prestressing ratio compared to other parameters. Furthermore, a comparison was conducted of the Chinese code, Eurocode and ACI standard for evaluating the flexural strength of CPC beams using the established database. It shows that the three design codes overestimate the flexural strength of CPC beams, and it is unsafe to predict flexural strength using these three codes without taking into account the impact of corrosion. Finally, a practical model based on the ACI standard is suggested to provide precise and reliable predictions across a diverse set of test data.

Prestressed concrete box girders are commonly employed in the development of high-speed railway bridge constructions. The prestressed strands in the girder may corrode due to long-term chloride erosion, leading to the degradation of its flexural performance. To examine the flexural performance of corrosion-affected simply supported prestressed concrete box girders, eight T-shaped mock-up beams related to the girders used in the construction of high-speed railway bridges were manufactured utilizing similarity theory. Seven of the beams underwent electrochemical accelerated corrosion, and then each beam was subjected to failure under the four-point load test method. Measurements recorded and analyzed in detail during the loading process included the following: crack propagation, crack width at various loads, crack load, ultimate load, deflection, and concrete strain of the mid-span section. The results demonstrate that a corrosion rate of just 8.31% has a considerable impact on the structural integrity of the beams, as evidenced by a pronounced reduction in flexural cracks and a tendency towards reduced reinforcement failure. Furthermore, the corrosive process has a detrimental effect on mid-span deflection, ductility, and ultimate flexural bearing capacity, which could have significant implications for bridge safety. This study provides valuable insights for the assessment of flexural performance and the development of appropriate maintenance strategies for corroded simply supported box girders in high-speed railways.