The utilization of waste rubber as a viable option for manufacturing building materials holds great significance for the sustainable development of the construction industry. This study explores the addition of two additives, fly ash (FA) and glass fiber (GF), to rubberized mortar in order to improve its performance. The impact of different waste rubber powder (RP) replacement rates and modified additive dosages on the performance of rubberized mortar, including fluidity, mechanical properties, drying shrinkage, impact resistance, and thermal insulation properties, was investigated. Furthermore, the analytic hierarchy process (AHP) was adopted to study the priorities of the rubberized mortar modified by FA and GF. The results indicate that the addition of RP leads to a decrease in mortar fluidity, mechanical properties, and drying shrinkage. However, it can enhance its impact resistance and thermal insulation properties. The additives, FA and GF, have a significant influence on the properties of rubberized mortar. By means of AHP method analysis, this study concludes that the optimal comprehensive properties of FA- and GF-modified rubberized mortar can be achieved by replacing 10% of sand with RP and using 10% FA and 0.4% GF. This study presents a configuration method for modified thermal insulation rubberized mortar, and it may lead to FA and GF being considered potential candidates for developing environmentally friendly building materials.

With the development of the automotive industry, a large amount of waste rubber is produced every year. The application and development of recycled rubber concrete (RRC) can effectively reduce ‘black pollution’ caused by waste rubber. However, the addition of recycled rubber particles can lead to a decrease in the compressive behavior of concrete. Previous research has demonstrated that by preventing crack growth, fiber addition can increase the strength and ductility of concrete. In this work, a total of 28 RRC mixes are designed, and the compressive behavior of RRC reinforced by steel fibers (SFs) and glass fibers (GFs) is investigated. The workability of fresh RRC can be negatively impacted by an increase in both fiber contents, with the GF content having a more notable effect. With the addition of fibers, the maximum increase rates for the compressive strength, elastic modulus, strain at peak stress, and compressive toughness were 27%, 8%, 45%, and 152%, respectively. A constitutive model is concurrently put forward to forecast the stress–strain curves of RRC with various fiber contents. These findings indicate that the maximum improvement in compressive behavior is achieved when the GF content was 0.4% and the SF content was 1.2%. The proposed constitutive model can be used to predict the stress–strain curve of hybrid fiber-reinforced recycled rubber concrete (HFRRRC).

The new composite application of seawater sea sand concrete (SSC) and fibre-reinforced polymer (FRP) bars had broad development prospects. In this paper, the load levels and stirrup spacing were the main research parameters. The fatigue behaviour of carbon fibre-reinforced polymer (CFRP) bar-reinforced SSC beams was studied by four-point bending tests, and the development laws of fatigue crack width and fatigue deflection were deeply discussed. Results revealed that excessive stirrup spacing might change static failure modes of CFRP bar-reinforced SSC beams, resulting in a reduction in mechanical behaviour. This paper preliminarily suggested that the maximum stirrup spacing should be 200 mm. The fatigue failure mode of CFRP bar-reinforced SSC beams in this paper was mainly shear fatigue failure. The fatigue crack width and fatigue deflection increased with the cycle number. When the cycle number reached 80% of fatigue life, the fatigue crack width increased by about 100%. When the beam specimens were close to fatigue failure, the increase in fatigue deflection ranged from 166.5% to 188.9%. Load levels had a significant impact on fatigue life, and a fatigue limit of 0.5 was proposed as a threshold. In addition, the larger the stirrup spacing, the greater the growth rate of fatigue crack width and fatigue deflection. Therefore, based on the calculation equation for the maximum crack width in the code, the influence of stirrup spacing, load levels and n/N was further considered in this paper. Considering the influence of stirrup spacing and load levels, a calculation equation for fatigue deflection was proposed. Finally, the fatigue design concept was improved, and the fatigue life was further subdivided into the fatigue life on bearing capacity and normal service.

Rubberized concrete exhibits enhanced toughness and sustainability but suffers from reduced mechanical strength, limiting its applications. This study enhanced the compressive strength of rubberized concrete using hybrid steel/glass fibers. The results showed a positive synergy between the hybrid fibers, with improvements in compressive strength, elastic modulus, Poisson’s ratio, peak strain, and compressive toughness by 16.1%, 19.4%, 32.0%, 63.4%, and 101.7%, respectively, at a hybrid fiber content of 0.8% (steel fiber 0.6% and glass fiber 0.2%). A well-fitting stress–strain model was adopted for future constitutive simulations. This study advances the understanding of rubberized concrete with hybrid steel/glass fibers under axial compression and promotes its application in structural engineering.

As an environmentally friendly construction material, recycled rubber concrete (RRC) is commonly used as a road material owing to its excellent flexural strength and crack resistance. Previous studies have shown that the addition of fibres is an effective method for improving the crack resistance of concrete. The purpose of this study is to investigate the fracture performance of RRC reinforced with steel fibres (SFs) and glass fibres (GFs). A total of 28 RRC mixtures were prepared. The results of the fracture test showed that the addition of SFs and GFs significantly enhanced the RRC fracture performance. The maximum increases or decreases in flexural strength, brittleness coefficient, fracture energy, initial fracture toughness, and unstable fracture toughness were 64.9, −34.6, 775.6, 92.0, and 118.4%, respectively. The ideal GF content is usually in the range of 0.4–0.6% and decreases with increasing SF content. In addition, scanning electron microscope (SEM) tests were conducted to explore the mechanism of the effect of hybrid fibres on RRC at a microscopic level. The results show that SFs were always pulled out, while GFs were pulled apart at the initial defects. At the same time, excessive GFs caused more initial defects. These results are expected to provide theoretical direction and experimental support for the practical application of hybrid fibre-reinforced recycled rubber concrete (HFRRRC).

Owing to the substantial benefits in environmental protection and resource saving, recycled aggregate concrete (RAC) is increasingly used in civil engineering; among the different types, RAC-filled steel tubes are an efficient structural form utilizing the advantages of concrete and steel tubes. This paper proposed a novel full-bolted beam-to-concrete-filled steel tube (CFST) joint and investigated the anchoring behavior of the steel plates embedded in RAC-filled steel tubes, which represents the behavior of the tensile zone in this joint, to demonstrate the feasibility of utilizing RAC in composite structures. The specimen consisted of a CFST and a connecting plate embedded in the CFST. In total, 18 specimens were tested to study the effects of concrete type (i.e., recycled aggregate concrete and natural aggregate concrete), anchoring type (i.e., plate with holes, notches, and rebars), and plate thickness on the pullout behavior, such as anchorage strength, load–displacement response, and ductility. Based on experimental results, the aggregate type of the concrete does not affect the pullout behavior obviously but the influence of anchoring type is significant. Among the three anchoring methods, the plate with rebars exhibits the best performance in terms of anchorage strength and ductility, and is recommended for the beam-to-CFST joint. In addition, plate thickness obviously affects the behavior of plates with holes and notches, the bearing area of which is proportional to the thickness, whereas the pullout behavior of the plates with rebars is independent of thickness. Finally, design formulas are proposed to estimate the anchorage strength of the connecting plates, and their reasonability is validated using the experimental results.