Construction and Building Materials最新文献

Good workability, mechanical behavior, and durability are the prerequisites for the application of cementitious grout in engineering fields. To further promote the application of cementitious grout in the field of civil engineering, the research status of cementitious grout from the aspects of workability, mechanical behavior, and durability were systematically reviewed in this study, and future research directions and trends were predicted and analyzed. It is shown that the reasonable addition of supplementary cementitious materials, chemical admixtures, and fibers can improve the workability, mechanical behavior, or durability of cementitious grout. However, further research is needed on the mix proportion of cementitious grout that balances workability, mechanical behavior, and durability. Numerous studies have examined the constitutive behavior of cementitious grout under uniaxial compression. The results show that compared to ordinary concrete, cementitious grout exhibits a larger peak strain, smaller elastic modulus, larger proportional limit, and more obvious brittle characteristics. However, research is urgently needed on the constitutive behavior of cementitious grout under dynamic, repeated load or multi-axis and other complex stress states, as well as the constitutive behavior of cementitious grout constrained by stirrups. Corresponding theoretical or semi-theoretical constitutive models still need to be established. In terms of durability, cementitious grout shows better frost resistance and resistance to penetration of harmful ions than concrete due to the hardened slurry of cementitious grout having a more compact pore structure. The performance degradation of cementitious grout under freeze-thaw, and salt corrosion has been explored, but further research is needed on the degradation mechanism, as well as the ion diffusion coefficient model and ion transport model. In addition, cementitious grout may be subjected to multiple ion erosion or coupling effects of multiple factors during actual service, and thus, research on the durability of cementitious grout under the above-mentioned environmental coupling effects still needs to be carried out.

To improve the long-term durability and functionality of open graded friction courses (OGFC), the Florida Department of Transportation (FDOT) investigated the use of a highly modified asphalt binder and increased thickness using Accelerated Pavement Testing (APT). A total of six test sections with combinations of two modified binder types (PG 76–22 and PG 82–22) and three lift thicknesses of 0.75 (19.05 mm), 1.25 (31.75 mm) and 2 (50.8) inches were constructed at FDOT’s APT facility. Accelerated loading was performed using a Heavy Vehicle Simulator (HVS) to evaluate the relative rutting performance of the test sections. Supplementary field and laboratory tests to evaluate tensile strength, Cantabro loss, field permeability, surface characteristics, and asphalt binder properties were also conducted. Test results indicated that the use of PG 82–22 polymer modified asphalt (PMA) binder may be beneficial to improve long-term durability of the OGFC. Thicker layers of OGFC were found to have considerably lower durability. It is recommended that the use of a highly modified PMA asphalt binder in OGFC layers be considered when raveling and other durability issues are of concern.

To enhance the early performance of magnesium potassium phosphate cement (MKPC) and compensate for loose of compressive strength caused by the addition of boric acid (BA), triethanolamine (TEA) was incorporated in this work. This research was demonstrated that TEA hindered the dissolution of MgO and formed a complex with potassium ions, as evidenced by tests including compressive strength, hydration heat analysis, microstructure analysis, conductivity, and ion concentration. Furthermore, the study demonstrated that the addition of 2 wt% BA and 2 wt% TEA to MKPC resulted in a significant improvement in its characteristics, while only minimally affecting its early compressive strength. The compound was found to extend the setting time and enhance fluidity by 200 % and 32 % respectively, while also inhibiting the formation of K-type struvite. The hydration product type of MKPC did not change, and MKPC can reach an early compressive strength of 42.52 MPa at 24 h, only experiencing a slight reduction of 1.78 %.

Based on experimental studies, this paper proposes two efficient machine learning models to evaluate the macroscopic mechanical properties of recycled coarse aggregate self-compacting concrete (RCASCC) after sulfate freeze-thaw action. Initially, the stress-strain curves of RCASCC after sulfate freeze-thaw action were measured, yielding the peak stress (σ_c), peak strain (ε_c), and elastic modulus (E) for each group of RCASCC. Among these, a strong linear correlation was observed between the elastic modulus and the peak stress. An RCASCC uniaxial compression behavior model considering the effects of sulfate freeze-thaw cycles has been established. This model is used to predict the stress-strain characteristics of RCASCC under uniaxial compression after exposure to sulfate freeze-thaw cycles. Using the stress-strain data of uniaxial compression test, a machine learning model for RCASCC after sulfate freeze-thaw cycle was developed by using MATLAB. Eight different machine learning algorithms are used to train and test the model, and six performance indicators are used to measure its generalization performance. The three models, RF, ET and GB, exhibit the highest prediction accuracy compared to other machine learning models. The relative importance of strain and Na₂SO₄ mass fraction is largest and smallest in the three models, RF, ET and GB, respectively. Based on RF, ET and GB models with good predictive performance, we plot the stress-strain curves of the predicted models. The fit is better for the ascending and descending segments of the curves in each group, and worse for the curves near the peak. RF and ET can better predict the macroscopic mechanical properties of RCASCCC under different conditions.

Understanding the potential mechanism of in-situ polymerization of acrylamide (AM) for modifying seawater cementitious materials is crucial for designing high-strength and durable marine concrete. Herein, the acrylamide (AM) in-situ polymerization was investigated for its effects on the hydration behavior, micro-morphology, and pore structure of cementitious materials mixed with seawater and freshwater through a series of elaborately designed microscopic characterization methods. The results reveal that the hydration process of cementitious materials proceeds simultaneously with in-situ polymerization. However, compared with freshwater mixtures, seawater provides a large number of metal ions and SO₄^2- ions, which can cross-link with the generated polyacrylamide (PAM) during in-situ polymerization to form a three-dimensional network structure. The synergistic effect of the hydration, in-situ polymerization, and cross-linking processes of cementitious materials can improve the pore structure of seawater-mixed paste, enhance erosion resistance, and improve the stability and toughness of microstructure. These findings were further confirmed by comparing infrared spectroscopy results, hydration products, pore size, and micro-morphology analysis as well as flexural performance tests. This is of great significance to guide the design of novel materials in marine infrastructure.

This paper presents an experimental investigation into the compressive and shear resistance of triple-layered laminated steel-reinforced glass beams. Two types of tests are performed: (a) local compressive tests (force over a support) and (b) bending tests (force close to a support). In total, six local compressive tests and eight bending tests are performed. Overall, beams with a shear span-to-effective depth ratio (a/d) approximately equal to 0, 0.63, and 1.0 are tested. Two different types of flexural reinforcement are used separately: solid (S) and hollow (H) reinforcement. The behaviour of the outer glass panes, and top and bottom reinforcement is monitored using strain gauges and Digital Image Correlation (DIC). The test results are elaborated in terms of load-displacement curves, the evolution of strains and crack patterns. Three failure modes are observed: yielding of the reinforcement (PF), crushing of glass (CF), and rupture of the reinforcement (RR). Shear failure occurred due to the crushing of glass in the compressed diagonal strut in the shear span. It was found that the shear resistance increases with a smaller shear span-to-effective depth ratio and stronger reinforcement. The dominant shear transfer mechanism was the direct strut action. It was found that the post-fracture capacity had a relatively constant value for all the tests with a slight increase for smaller a/d. The actual tensile strains in the bottom reinforcement measured by DIC are compared with the calculated strains based on the curvature of uncracked and cracked cross-sections, assuming plane section behaviour. It was observed that the actual strains are systematically larger than the calculated ones because, in reality, the section does not remain plane. After the appearance of the first crack, the beams essentially behave like strut-and-tie systems, where the strut is the diagonally compressed laminated glass and the tie is the bottom reinforcement.

The length of timber beams of restricted commercial lengths can be increased by carpenter splices, which requires a thorough characterization of the flexural performance of these beams. An experimental study was carried out addressing timber beams joined with Jupiter ray splices to identify the influence of height-to-length (h:l) ratios of the splices on the mechanical performance in terms of deflection and flexural capacity. Jupiter ray splices with height-to-length (h:l) ratios of 1:2, 1:3, 1:4, and 1:5 were manufactured using computer-aided design (CAD) and computer-assisted manufacturing (CAM). The flexural performance of the tested beams was characterized in terms of modulus of rupture (MOR), modulus of elasticity (MOE), inelastic stiffness (K_inelastic), mid-span deflection (δ), and shear modulus values, measured using a four-point bending test setup under pure bending. Results indicate that implementing these joints reduces the flexural performance compared to equivalent solid timber beams without carpenter splices. The ratio concerning solid beams varies in ranges of 12–24 %, 26–43 %, 57–71 %, and 21–35 % of the corresponding solid beams average MOR, MOE, δ, and K_inelastic values, respectively. Moreover, a high linear correlation was observed between the average values obtained at the bending tests with h:l ratios in this study. Finally, the predominant failure patterns are described, identifying the critical points of stress concentration.