The addition of fibers to strengthen recycled concrete can strengthen the inherent deficits and deficiencies of concrete containing recycled aggregates to some extent and enlarge the concrete’s application range. In order to further promote the development and application of fiber-reinforced brick aggregate recycled concrete, the research results regarding its mechanical properties are reviewed in this paper. The effect of the content of broken brick on the mechanical properties of recycled concrete and the effects of different categories and contents of fiber on the basic mechanical properties of recycled concrete are analyzed. The problems to be solved in research on the mechanical properties of fiber-reinforced recycled brick aggregate concrete are presented, and the related research suggestions and prospects are summarized. This review provides a reference for further research in this field and the popularization and application of fiber-reinforced recycled concrete.

In recent years, wind energy has begun to receive a significant amount of attention as clean energy is utilised and demanded in large quantities, resulting in a sharp increase in the use of wind turbines. The demand for wind turbines has gradually risen due to the clean and recyclable nature of wind energy. The current blade life of wind turbines in China is about 20 years, which means that the disposal of obsolete used blades can become a difficult problem in the future. Therefore, this study is of great significance to explore the regeneration performance of the blades after recycling and disposal. In this paper, wind turbine blades were mechanically recycled into recycled macrofibres, which were added to concrete as a reinforcing material to make wind impeller fibre concrete (WIC), and the three proportion ratios of 1%, 1.5%, and 2% were explored to compare the performance. The performance of WIC was also evaluated and its performance was compared to that of glass fibre concrete (GC). In addition, the material physical properties of second-generation recycled aggregate concrete (RAC) based on WIC were explored. The strength and peak strain variations and their causal mechanisms were analysed both macroscopically and microscopically by means of the classical mechanical tests (compression and bending tests), SEM, and XRD. The results show that the compressive strength of WIC was negatively correlated with the fibre content and increased by 6.04–18.12% compared to that of ordinary concrete (OG), with a maximum of 19.25 MPa; the flexural strength was positively correlated with the fibre content, with an increase of 5.37–18.5%. The microstructural analysis confirmed the macroscopic results and the intrinsic model better validated the experimental results.

This paper investigates the mechanical and micro-interfacial properties of recycled concrete. Concrete specimens with recycled brick coarse aggregate (RBCA) admixtures of 0%, 25%, 50%, 75%, and 100% were prepared. Apparent density, slump, and mechanical tests were carried out to evaluate the properties and behavior of the recycled concrete. The evolution laws of parameters such as compressive strength, peak strain, and elastic modulus of the recycled concrete specimens were tested and analyzed. Combined with numerical analysis, the stress distribution and damage propagation process of recycled concrete specimens with different RBCA contents were revealed. Furthermore, the RBCA content parameters and the thickness of the interface transition zone were analyzed to predict the mechanical behavior of RBCA concrete. The results show that the slump of fresh recycled concrete is less than 50 mm when the content of RBCA exceeds 50%. The apparent density of concrete is 15.55% lower than that of ordinary concrete when the content of RBCA is 100%. The cube compressive strength of RBCA concrete decreases with increased RBCA content. With increasing RBCA substitution rate, the internal cracks change from discrete to concentrated. The substitution rate of RBCA and thickness of the interfacial transition zone are negatively correlated with compressive strength and positively correlated with elastic modulus and peak stress.

To predict the effect of chemical-freezing coupling erosion on the properties of four kinds of FRP-reinforced concrete. Rapid freeze–thaw tests were conducted. The mass loss rate, relative dynamic elastic modulus, compressive strength, and flexural capacity were tested to investigate the Mechanical Performance of specimens. The compression specimens are cylindrical specimens wrapped with FRP, and the flexural specimens are pasted with FRP prismatic specimens on the pre-cracked side. A database was built based on 45 groups of experimental test results, and the prediction effect of the BP neural network and CNN model on compressive strength and flexural capacity was compared, respectively. The results showed that CNN did a better job. Finally, the maximum number of freeze–thaw cycles of different FRP-reinforced specimens was predicted based on the CNN model with mass loss rate and relative dynamic modulus as the evaluation criteria. This method can provide a new perspective for predicting the durability of FRP-reinforced concrete.

Plain concrete specimens and FRP(Fiber Reinforced Polymer)-reinforced concrete specimens were fabricated to investigate concrete’s mechanical and surface degradation behaviors reinforced with carbon, basalt, glass, and aramid fiber-reinforced polymer under coupled sulfuric acid and freeze–thaw cycles. The compressive strength of fully wrapped FRP cylindrical specimens and the flexural load capacity of prismatic specimens with FRP reinforced to the pre-cracked surface, along with the dynamic elastic modulus and mass loss, were evaluated before and after acid–freeze cycles. The degradation mechanism of the specimens was elucidated through analysis of surface morphological changes captured in photographs, scanning electron microscopy (SEM) observations, and energy-dispersive spectroscopy (EDS) data. The experimental results revealed that after 50 cycles of coupled acid–freeze erosion, the plain cylindrical concrete specimens showed a mass gain of 0.01 kg. In contrast, after 100 cycles, a significant mass loss of 0.082 kg was recorded. The FRP-reinforced specimens initially demonstrated mass loss trends comparable to those of the plain concrete specimens. However, in the later stages, the FRP confinement effectively mitigated the surface spalling of the concrete, leading to a reversal in mass loss and subsequent mass gain. Notably, the GFRP(Glassfiber Reinforced Polymer)-reinforced specimens exhibited the most significant mass gain of 1.653%. During the initial 50 cycles of acid–freeze erosion, the prismatic and cylindrical specimens demonstrated comparable degradation patterns. However, in the subsequent stages, FRP reduced the exposed surface area-to-volume ratio of the specimens in contact with the acid solution, resulting in a marked improvement in their structural integrity. After 100 cycles of acid–freeze erosion, the compressive strength loss rate and flexural load capacity loss rate followed the ascending order: CFRP-reinforced < BFRP(Basalt Fiber Reinforced Polymer)-reinforced < AFRP(Aramid Fiber Reinforced Polymer)-reinforced < GFRP-reinforced < plain specimens. Conversely, the ductility ranking from highest to lowest was AFRP/GFRP > control group > BFRP/CFRP. A probabilistic analysis model was established to complement the experimental findings, encompassing the quantification of hazard levels and reliability indices.

During the ice-breakup period in cold regions, the impact of drifting ice floes on bridge piers readily induces extreme ice loads and structural damage, and because the ice is transported continuously by the flow, a pier is subjected to a sustained crushing process rather than a single free collision. Conventional protective techniques suffer from insufficient durability, whereas fiber-reinforced polymer (FRP) offers protective advantages owing to its light weight, high strength, and corrosion resistance. However, the differences in ice-impact protective performance among carbon (CFRP), glass (GFRP), basalt (BFRP), and aramid (AFRP) fiber composites remain unclear. In this study, ANSYS/LS-DYNA is employed to construct an explicit dynamic finite element model of continuous ice-floe impact on an FRP-strengthened bridge pier, in which the sustained driving action of the flow is represented by a constant-velocity boundary prescribed at the trailing edge of the ice. The elastic constants of ice are calibrated and the material parameters verified against published ice-concrete collision test data, reducing the relative error of the maximum impact stress from 22.5% to 7.89%; a purpose-designed scaled-model ice-pier impact flume test is further used for qualitative verification of the collision process. On this basis, 20 full-factorial parametric cases are designed to systematically examine the influences of ice-floe velocity, ice volume, and FRP type on the impact force, stress distribution, displacement response, and energy dissipation. Within the investigated parameter ranges and modeling assumptions, the results show that: (1) the peak impact force is governed mainly by the effective ice-pier contact area and the crushing strength of ice; for the unstrengthened pier, doubling the ice velocity raises the peak force by only 3.3–4.7%, and doubling the ice volume changes the peak force by only 1.5–2.7%; (2) the reduction in the peak impact force by FRP is strongly dependent on the ice condition, material differences appearing only under the small-volume, low-velocity condition (21.7–29.5%) and amounting to less than 0.1 percentage point under the other conditions; in terms of the mean impact force, CFRP is the only scheme that achieves a reduction under all ice conditions, with a mean reduction of 18.0% over the four conditions, superior to AFRP (12.3%), GFRP (9.5%) and BFRP (9.1%), although this ranking applies to the 5 mm equivalent shell and is thickness-dependent; (3) at the representative instant t = 0.2 s the peak von Mises stress of the pier decreases from 3.201 MPa to 1.111–1.693 MPa, a reduction of 47.1–65.3%, showing a far higher sensitivity to FRP type than the peak impact force; (4) the peak stress in the four FRP sheets amounts to only 0.21–0.36% of their fiber-direction tensile strength and their internal energy is close to zero, indicating that, within the present configuration (a 5 mm equivalent FRP shell held against the pier by a frictional, unbonded contact interface), the protective effect of FRP derives mainly from local stiffness enhancement and load diffusion rather than from tensile load carrying or energy absorption. The above mean impact forces and energy quantities are values truncated at t = 0.5 s. This study quantifies the differences in ice-impact protective performance among FRP types and provides a numerical reference for FRP selection and ice-resistant design of bridge piers in cold regions within the investigated parameter ranges. These findings, in particular the weak velocity sensitivity, are conditional on the adopted rate-independent ice model, which does not represent the strain-rate dependence of ice strength.