Main cable line shape measurement and parameter identification are a critical task in the construction monitoring and service maintenance of suspension bridges. 3D LiDAR scanning can simultaneously obtain the coordinates of multiple points on the target, offering high accuracy and efficiency. As a result, it is expected to be used in applications requiring rapid, large-scale measurements, such as main cable line shape measurement for suspension bridges. However, due to the large span and tall main towers of suspension bridges, the LiDAR field of view often encounters obstructions, making it difficult to obtain high-quality point clouds for the entire bridge. The collected point clouds are typically unevenly distributed and of poor quality. Therefore, LiDAR is used to monitor the local cable line shape. This paper proposes an innovative non-uniform sampling method that adjusts the sampling density based on the main cable’s rate of change. Additionally, the Random Sample Consensus (RANSAC) algorithm, the ordinary least squares, and center-of-mass calibration are applied to identify and optimize the geometric parameters of the cross-section point cloud of the main cable. Given the strong design prior information available during suspension bridge construction, Bayesian theory is applied to predict and adjust the global line shape of the main cable. The study shows that using LiDAR for cable point cloud measurement enables rapid acquisition of high-precision point cloud data, significantly enhancing data collection efficiency. The method proposed in this paper offers advantages such as highly automated, low risk, low cost, and sustainability, making it suitable for green monitoring throughout the entire main cable construction process.
The study of frost resistance of recycled concrete (RC) can provide a theoretical reference for assessing its safety and durability for service in cold environments, thereby facilitating the engineering application of sustainable construction materials. To verify the feasibility of replacing cementitious materials with recycled fine powder (RFP), cement paste was prepared by substituting RFP for cementitious materials by mass fraction at 0, 10%, 20%, and 30%. The microstructures were characterized by X-ray diffraction (XRD), thermogravimetry (TG), and scanning electron microscope (SEM). And the results presented that the incorporation of 10% RFP promoted the hydration of cementitious materials. Subsequently, the effect of the addition of recycled fine aggregate (RFA) and RFP on the frost resistance of RC was investigated. River sand and cementitious materials were separately replaced by RFA and RFP at a mass fraction of 0–30%, and various properties of the RC were tested after different numbers of freeze–thaw cycles (FTCs), including the relative dynamic elastic modulus (RDEM), mass loss rate, compressive strength, and microstructural morphology. The results revealed that RFP was highly sensitive to low-temperature environments, with specimens containing only RFP failing under fewer than 100 FTCs. However, the addition of RFA helped improve the frost resistance of RC by filling microcracks and reducing water infiltration. Optimal frost resistance of the RC was achieved when the mass fractions of RFP and RFA reached 10% and 30%, respectively, with an RDEM value of 69.65%, a mass loss rate of 1.32%, and a compressive strength of 15.7 MPa after 200 FTCs.
This study investigates the mechanical properties and stress-strain relationship of recycled stone masonry aggregate (RSMA) concrete with varying replacement ratios. Using a three-graded RSMA (5–60 mm), the research was further validated through its application in the reconstruction project of the Kada Reservoir dam. The results reveal that as the replacement ratio of RSMA increases, there is a corresponding decrease in compressive strength, splitting tensile strength and elastic modulus. The ascending section of the dimensionless stress-strain curve of RSMA concrete exhibits a pattern comparable to that of natural aggregate concrete. As the aggregate replacement ratio increases, the descending portion of the stress-strain curve for RSMA concrete becomes steeper. To model the behavior of three-graded RSMA concrete, the constitutive equation for two-graded recycled aggregate concrete was applied. This study provides a critical foundation for the regeneration and utilization of slurry masonry dams, offering both theoretical insights and practical guidance for sustainable dam reconstruction projects.
In the context of sustainable development, earthen building materials could be a viable alternative to conventional, energy-intensive materials if the constraints to their general acceptance and widespread use are mitigated. A key challenge is the limited understanding of how intrinsic soil properties influence the performance of these materials. This study investigates the role of intrinsic iron oxides and calcium carbonate, components that are believed, yet not conclusively proven, to exert a strong influence on earthen materials by increasing strength and reducing shrinkage through aggregation and cementation mechanisms. Engineered soils based on kaolin powder, bentonite powder, and a natural clayey soil were prepared and combined with ferric oxide, iron powder, and fine limestone powder to produce mortars. Mortars with iron and iron oxides exhibited no significant improvement in compressive strength, a finding attributed to the high crystallinity and low solubility of the oxides used, as well as to the alkaline pH of the soils. In contrast, mortars containing limestone powder exhibited remarkable strength gains across all soil types, demonstrating that intrinsic CaCO3, particularly its finer and more reactive fraction, can positively impact strength development. Further analysis, including pH cation exchange capacity (CEC) and exchangeable calcium measurements, revealed that limestone powder actively interacts with the soil’s exchangeable complex, driven by its significant active calcium carbonate (ACC) content. These results underline the importance of soil chemistry in the performance of earthen building materials.
Carbon emissions from engineering construction play a critical role in achieving urban carbon peak and neutrality goals. This study evaluates the carbon emission reduction benefits of the renovation project of Yihe Bridge on Beijing Road using a life cycle assessment (LCA) approach. The carbon emissions resulting from the renovation were compared with those of an alternative demolition and reconstruction plan. The calculation boundary for carbon emissions during the bridge construction period was defined based on the renovation project’s specifics, dividing the process into three stages: material production, material transportation, and mechanical construction. By integrating factor decomposition theory with the carbon emission factor method, a carbon emission mode was developed, allowing a comprehensive quantitative analysis for the construction period. Results indicate that total carbon emissions were 84 560.40 t, with material production contributing 94.73%, transportation 1.47%, and mechanical construction 3.80%. The carbon emission intensity of the newly expanded bridge section was 2.11 t/m2. Compared to the demolition and reconstruction, the renovation plan reduced carbon emissions by 53 643.44 t, achieving a 38.81% reduction.
Renowned for its outstanding strength, durability, and resistance to cracking, ultra-high performance concrete (UHPC) relies on the careful selection of materials and mix design to achieve the ideal combination of extreme strength and fluidity. This study utilized the simplex centroid design (SCD) method to conduct a multifactor interaction analysis aimed at optimizing the mix proportion of UHPC matrix. The optimized UHPC was then evaluated for its performance. Statistical models were developed to examine the connections between the characteristics (including fluidity, flexural and compressive strength) and the proportions of cement, silica fume, fly ash, and sinking beads of the UHPC matrix employing the SCD method. The models considered four cementitious materials and their interactions. Analysis of variance (ANOVA) was utilized for validation, resulting in the generation of response surfaces and contour plots. These visualizations offered insights into the effect of individual and interactive variables on UHPC matrix performance. Subsequently, the test mix proportions were determined according to the specified performance requirements, and end-hooked steel fibers were incorporated into the mixtures to produce UHPC. The thoroughly evaluated optimized UHPC showed enhanced workability, mechanical properties, durability, and microstructural characteristics. Furthermore, it exhibited improved resistance to chloride ion penetration and superior long-term drying shrinkage behavior when compared to standard concrete.
To mitigate the shortage of river sand and promote the reuse of construction waste, this study comprehensively evaluates the applicability of completely recycled fine aggregate (CRFA), produced by crushing concrete waste completely into fine aggregates, in structural concrete from the material to structural levels. Mechanical properties, durability, shrinkage, microstructure, and structural performance of recycled aggregate concrete (RAC) with CRFA as the sole fine aggregate were tested and compared to natural aggregate concrete (NAC) of the same strength grade. The results indicate that RAC exhibits comparable strength and elastic modulus to NAC at 28 days, although its long-term compressive strength is 12% lower. RAC demonstrates superior freeze–thaw resistance but reduced resistance to carbonation and chloride ion penetration due to a higher percentage of large pores, as observed via mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM). RAC also shows lower early-age autogenous shrinkage but higher long-term drying shrinkage than NAC. Structural testing under bending, axial, and eccentric compression reveals that RAC performs similarly to NAC and can be conservatively predicted by current design codes for NAC, with the ratios between experimental and predicted values exceeding 1.08. Furthermore, with 18.8% and 10.5% reductions in cost and carbon emissions, respectively, CRFA is an economical and sustainable alternative to river sand in structural applications.
This study innovatively develops high-strength geopolymers for grouting materials with a high recycled concrete powder (RCP) usage of 60% to meet engineering needs. It investigates the impact of slurry synthesis parameters such as the mass ratio of RCP to granulated blast-furnace slag (rRP/GS), water glass modulus (Ms), alkali equivalent (rAE), and the ratio of water mass to solids mass (rL/S) on the properties of high-performance geopolymer grouting materials (HRCP-GP). The results reveal the optimal parameter intervals: rRP/GS = 60:40, Ms = 1.2 – 1.4, rAE = 7% – 9%, and rL/S = 0.38 – 0.40. Under these conditions, especially when w(RCP) is 60%, Ms = 1.4, rAE = 9%, and rL/S = 0.40, the 28 d compressive strength of the slurry reaches 45.81 MPa, ensuring excellent solidification flow properties. Microscopic analyses show that at the optimum alkali excitation ratio, the inert crystallites in RCP are efficiently solubilized and polymerized to form a dense three-dimensional network structure coexisting with C-(N)-A-S–H and C-(A)-S–H gels. This study provides a new approach for the development and application of sustainable grouting materials.
The integration of waste carbon fibre materials, specifically shredded prepreg carbon cloth waste (SPCCW) and discarded carbon fibre-reinforced polymer (DCFRP), presents a sustainable and innovative approach to enhancing the structural performance of concrete. This study evaluates the impact of these waste materials on the axial compressive strength, crack propagation, and failure mechanisms of reinforced concrete. Experimental findings revealed that SPCCW-reinforced concrete exhibited a 17.4% increase in strength at an optimal 1.5% fibre dosage, while DCFRP-reinforced concrete achieved an 18.8% improvement in strength at a 1.0% dosage. Excessive fibre content, however, negatively impacted performance, particularly in SPCCW mixtures, due to clustering effects and reduced matrix homogeneity. Numerical simulations, conducted using the ABAQUS software and the concrete damaged plasticity (CDP) model, provided an accurate representation of the nonlinear behaviour of concrete under axial compressive loading. Fibre distribution and orientation were modelled using Monte Carlo and pseudo-random methods to replicate real-world variability. Simulated results demonstrated excellent alignment with experimental data, achieving a maximum error of just 0.84%, validating the robustness of the model. Stress distribution and crack propagation analyses revealed the superior confinement effect of DCFRP fibres and the crack-bridging ability of SPCCW fibres, which enhanced stress redistribution and delayed failure. These findings underscore the dual benefits of incorporating waste carbon fibres into concrete by improving its mechanical properties while addressing environmental concerns through industrial waste reduction.
This study investigates the damage modes and cracks development patterns of recycled aggregate concrete (RAC) and ultra-high-performance concrete (UHPC) push-off specimens under direct shear. The experimental results reveal three distinct damage modes for specimens with varying numbers of shear keys: failure along the RAC-UHPC interface, failure along the interface on one side and around the interface on the other, and failure completely around the interface. Specimens with shear keys (R-U-1K, R-U-2K, and R-U-3K) demonstrated increases in ultimate shear stresses of 13.6%, 6.4%, and 18.2%, compared to the control specimen (R-U-m). Digital image correlation (DIC) analysis demonstrated that specimens with shear keys predominantly exhibited stress concentration in horizontal or vertical directions, leading to tensile-shear damage. A finite element model (FEM) was used to simulate and analyze the behavior of the push-off specimens, with results aligning well with the experimental findings. The findings confirm the feasibility of employing UHPC shear keys to increase bearing capacity of RAC-UHPC composite members. These insights are valuable for optimizing the design and promoting the high-value engineering application of RAC in composite structures.
The present study evaluates the effect and advantages of the combined use of two treatments on fiber-cement composites: 1) accelerated carbonation on the cement matrix and 2) hornification of commercially used unbleached pine pulp (Pinus radiata D. Don). The premise of the study was to develop a composite with superior physical–mechanical performance, increased durability, all within a sustainability context. Chemical, physical, and morphological characterization of the pulps with and without treatment was conducted. For fiber-cement composites, instrumental techniques such as XRD, TGA, SEM, and physical–mechanical characterization (before/after accelerated aging) were applied. The heat treatment does not deteriorate the pulps and reduces their hygroscopicity. Accelerated carbonation enhanced matrix mechanical properties, increasing modulus of rupture by 51% and specific energy by 154%. The mass fraction of Ca(OH)₂ decreased from 11.1% to 0.3%, while the mass fraction of CaCO₃ increased from 37.0% to 60.2%. After 200 cycles of accelerated aging, composites with accelerated carbonation or treated pulps showed pulp preservation and matrix densification. Composites with combined treatments exhibited the best performance and durability before and after accelerated aging. The potential and feasibility of applying these combined treatments to fiber and matrix are established from technical, economic, and environmental perspectives.
This study investigates the influence of growth ring orientation on the shear behavior of engineered timber, with the objective of improving the structural performance and optimizing the design of cross-laminated timber. Four groups of spruce-pine-fir samples with different growth ring orientations were selected for analysis: 6° (Group H), 37° (Group I), 85° (Group J), and with the pith at the center of the sample (Group K). V-notch shear tests (Iosipescu shear tests) were carried out by ASTM D5379/D5379M-19. The test results showed significant differences in shear performance among specimens with different growth ring orientations. In particular, Group I and Group K exhibited the higher shear performance, with average shear strengths of 3.89 MPa and 4.25 MPa, and shear moduli of 376.92 MPa and 270.38 MPa, respectively. In contrast, Group J showed the lowest shear performance, with an average shear strength of 2.13 MPa and a shear modulus of 56.85 MPa. The shear properties of Group H were intermediate between those of Group I and Group J, with an average shear strength of 3.00 MPa and a shear modulus of 149.53 MPa. Analysis of the load–displacement curves and stress–strain curves indicated that Group I and Group K had higher yield strength and stiffness before failure, while Group J exhibited better ductility.