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.
Extending the lifetime of existing nuclear facilities is becoming in-creasingly relevant to ensure the continued generation of electricity with a low carbon footprint. For this purpose, a thorough assessment is required of the potential pathologies that may arise and affect the integrity of existing concrete support structures. Of particular interest are internal swelling reac-tions, such as delayed ettringite formation (DEF) and alkali-silica reaction (ASR), which can cause swelling and cracking of concrete. While these pro-cesses have been well-researched at a laboratory scale, controlled studies at a larger scale are more scarce. To simulate the effects of these processes on a larger scale, concrete mock-ups were constructed, subjected to elevated tem-perature and humidity, and monitored, after which the mock-ups were sam-pled for further characterization. The purpose of this study was to conduct a detailed investigation of this type of concrete to assess whether the macro-scopic effects of the swelling reactions had a significant impact on the mi-crostructure and mineralogy, i.e. to investigate the effect of the dissolution or precipitation of phases induced by internal swelling reactions. The findings indicated that the bulk mineralogy and pore size distribution of the concrete samples were not significantly altered by either DEF or ASR. However, elec-tron microscopy imaging revealed significant amounts of cracking across all samples, which was associated with infilling by either ettringite crystals or ASR gel, depending on the mock-up. The infilling of cracks explains the lim-ited effect of either process on the overall pore size distribution. Although the overall volumetric expansion in the mock-ups was significant, it was primarily associated with heterogeneous large-scale cracks, with only minor contributions from the microscopic fractures.
This study aims to explore the feasibility of using circulating fluidized bed fly ash (CFA) as a supplementary cementitious material in both ordinary concrete and recycled aggregate concrete (RAC). Various properties of both concretes, including compressive strength, drying shrinkage, carbonation resistance, surface resistivity, were evaluated. Additionally, the economic and environmental benefits were assessed. Findings indicated that increasing CFA content (mass fraction) progressively increases drying shrinkage rate and carbonation depth in both concretes. At 30% CFA, ordinary concrete showed 10.9% higher 180-day shrinkage and 4.3% greater 28-day carbonation compared to the control, while RAC exhibited 14.7% higher shrinkage and a significant 34.4% increase in carbonation compared to its control. However, at 10% CFA, both concretes showed no significant reduction in compressive strength compared to their respective controls. Up to 20% CFA, a decline of 13.1% and 9.0% was observed in the 28-day compressive strength of ordinary concrete and RAC, respectively. The results indicate that RAC demonstrates better compatibility with CFA compared to ordinary concrete. Additionally, the economic and environmental benefit analysis showed that the lowest cost (8.6 and 7.4 yuan for ordinary concrete and RAC, respectively) and carbon emission (6.2 and 6.7 kg for ordinary concrete and RAC, respectively) for both concretes (normalized per unit of strength) occurred at 10% and 20% CFA, respectively. This study investigated varying CFA dosages to balance performance trade-offs against cost and carbon emissions, establishing the feasibility of CFA utilization in both ordinary concrete and RAC.
Timber–concrete composite floor is an emerging option for the construction industry, and some recent works have studied the effect of inclined connectors in such a system. However, parameters influencing their mechanical behaviours have not been extensively studied. Hence, this study examines the influence of the different components using a newly developed non-linear finite element (FE) modelling. The developed FE model was validated using experimental data available in the literature. The non-linear behaviour was considered as an elastoplastic hardening material model incorporating Hill’s yield criterion. Subsequently, the FE model was used to conduct a parametric study to examine the influence of several parameters on the mechanical response of the composite floor. The study revealed that the concrete strength played an essential role in the overall strength of the beam and ductility. Increasing the concrete strength from 21 MPa to 35 MPa led to an increase in load carrying capacity by 31.9%. Varying the timber properties variables (tensile strength and elastic modulus) and shear connectors arrangement resulted in changes in the overall strength but also the stiffness of the composite. The load carrying capacity ranged from −2.12% to 6.55% and the deformation decreased by up to 28.98% for the GL36h sample. In addition, the comparison of the plastic moment resistance of each condition was probed, indicating an impactful influence on the plastic stress distribution between all major parts of the composite system. In general, increasing the timber grade resulted in a drop in the plastic moment whereas increasing the concrete strength increased the plastic moment resistance.
Traditional non-destructive evaluation (NDE) methods often suffer from insufficient sensitivity in detecting early-stage microcracks and lack real-time monitoring capability. To overcome these limitations, this study conducted four-point bending fatigue tests on notched beam specimens under loading frequencies of 10 Hz and 15 Hz. During testing, the primary acoustic emission (AE) parameters—amplitude, energy, rise time, and duration—were systematically analyzed. In addition, information entropy was introduced to characterize signal randomness, while the maximum Lyapunov exponent (MLE) was employed to evaluate the chaotic characteristics of crack evolution, thereby revealing the staged damage evolution process. The results showed that amplitude was superior to other parameters in tracking fatigue damage, with its coefficient of variation (CV) remaining below 20%. Its evolution clearly corresponded to the four physical processes: pore compaction (Stage I), microcrack initiation (Stage II), stable propagation of macrocracks (Stage III), and catastrophic failure (Stage IV). Amplitude entropy exhibited distinct fluctuations across different stages, while MLE analysis further revealed the inherent disorder of crack evolution, with its variation validating the characteristics of each damage stage. Based on the coupled entropy–MLE framework, predictive thresholds (entropy > 10, MLE > 0.15, amplitude CV > 10) were proposed. Compared with conventional approaches, this framework enabled earlier identification of metastable crack propagation and effectively reduced false alarm rates. These findings demonstrate that the synergy of entropy and chaos analysis holds significant potential for NDE applications, offering new perspectives and methods for data-driven decision-making in pavement engineering.
Exploring the economic impacts of embodied carbon emissions is significant for achieving sustainable development in construction projects. However, the quantitative assessment of carbon costs in prefabricated buildings remains lacking. Therefore, this study proposes a method to assess the embodied carbon costs of prefabricated building projects. First, this method clarifies the boundary scope of embodied carbon. After obtaining the PCXML bill of quantities through building information modeling (BIM), it quantifies embodied carbon emissions. Then, the corresponding damage carbon costs are calculated through a monetary valuation model (ReCiPe). Finally, interpretation and optimizations are carried out. In the case study of a prefabricated substation, its embodied carbon costs are concentrated in the raw material production stage (74.4%), while using renewable concrete and renewable steel bars can reduce carbon costs by 21.6%. The case results also show that embodied carbon emissions exacerbate human malnutrition, and its carbon cost ranks first among various damages (42.7%). By evaluating the embodied carbon costs of prefabricated substations, this study helps project stakeholders comprehensively understand the external diseconomy of carbon emissions.
Synthesizing alkali-activated materials (AAM) with multi-component feedstock is a promising technology for resource utilization of massive industrial wastes, and there is an urgent need to develop proportional design methods. A thermodynamic modeling assisted design method was proposed for the fly ash (FA)-granulated blast furnace slag (GBFS)-steel slag (SS) AAM, of which the mechanical properties and multi-scale shrinkage were modified by incorporating graphene oxide (GO). The FA/GBFS mass ratio and SS content had a significant effect on the solid–liquid and crystalline phases, consistent to the thermogravimetric analysis and mechanical performances of the AAM. For the optimized FA:GBFS:SS mass ratio of 3:5:2, the mechanical strengths increased with the increment of GO content, then decreased, while the shrinkages at different stages and scales followed the opposite trend. At a GO dosage of 0.01%, the compressive, flexural, and tensile strengths increased by 9.6%, 67.1%, and 135%, respectively, while the chemical, autogenous, and drying shrinkage were reduced by 43.2%, 26.5%, and 46.1%, respectively. These modifications were mainly attributed to the refined pore structure and decreased micro-cracks of AAM through bridging and filling effects of GO, and the increased formation of C(N)-A-S–H gels thanks to the raised nucleation sites by the high specific surface areas of GO.
The lack of periodic safe disposal of silico-manganese wastes poses significant environmental and health risks. Producing each ton of silico-manganese alloy results in more than one ton of slag and 10%–15% fume, which can supplement cement in concrete. This study presents the first critical review of silicomanganese fume (SiMnF) for the synthesis of cementitious composites and evaluation of engineering properties. The review covers the fresh, hardened, and durability characteristics, along with the microstructural development of SiMnF-based Portland cement and alkali-activated products. It also examines the synergistic effects of SiMnF with other supplementary cementitious materials, focusing on rheological and mechanical aspects. The findings indicate that pre-treatment of raw materials and post-treatment of composites are essential for achieving target properties. Optimized dosage of SiMnF, alkaline activator concentration, and curing conditions can provide workable mixes with compressive strengths of up to 50 MPa. A detailed life-cycle assessment was conducted to quantify the environmental impact of SiMnF-based mixtures. Based on identified knowledge gaps, the study proposes a roadmap for future research. This review highlights the strategies for SiMnF from ferroalloy plants to be used in the cement and concrete industries, promoting solid waste management, reducing carbon footprints, and supporting sustainable development towards net-zero emission targets.
To explore the feasibility of recycling industrial waste as building materials, this study developed an environmentally friendly, low-carbon pervious concrete (PC). This study used coal gangue micro-powder (CGMP) and ground granulated blast furnace slag (GGBS) as supplementary cementitious materials to partially replace cement. Coal gangue sand (CGS) was used as fine aggregate, while municipal solid waste incineration slag (MSWI) and natural crushed stone aggregate (NCA) were used as coarse aggregates. The study investigated the effects of single-doping of CGMP (proportions: 10%, 20%, 30%, 40%) and composite doping of CGMP and GGBS (total admixture amount of 30% with CGMP-to-GGBS ratios of 1:1, 1:2, and 2:1) on the compressive, splitting tensile, and flexural strength, permeability, pore structure, and frost resistance of PC. Additionally, carbon dioxide (CO2) emissions and cost analyses were conducted. The results showed that single-doping of CGMP led to a decline in the mechanical properties and a deterioration of the permeability of PC. When the two materials were co-doped at a ratio of 1:2, the specimens exhibited a synergistic improvement in mechanical properties, although the permeability decreased. The 7-day and 28-day compressive strengths were 19.8 MPa and 24.6 MPa, respectively, and the permeability coefficient was 1.9 mm/s. In terms of freeze–thaw resistance, increasing the proportion of GGBS in the composite doping of mineral admixtures could improve frost resistance. Furthermore, the loss rate of compressive strength proved to be the most sensitive indicator of freeze–thaw effects, making it the most suitable parameter for durability assessment. In terms of carbon efficiency, life cycle assessment (LCA) indicates that compared with normal concrete pavement (NCP), the life-cycle carbon emissions per cubic meter of PC pavement prepared by the G10S20 scheme (a composite doping scheme with a total admixture content of 30%, including 10% CGMP and 20% GGBS) are reduced by 14.28% (from 410.148 kg CO2e to 351.577 kg CO2e), and by 14.80% compared with normal pervious concrete pavement (NPCP). In addition, cost analysis confirms that the construction cost of G10S20 pavement is 22.38% lower than that of NCP and 14.46% lower than that of NPCP. This material can effectively alleviate urban waterlogging, mitigate the heat island effect, and has both low-carbon and economic advantages when applied in scenarios such as urban roads, squares, and park ground paving. It thus provides practical evidence for the promotion of sustainable building materials.
This study systematically reviews the utilization of fiber-reinforced recycled ceramic waste concrete, focusing on its mechanical performance and environmental benefits. Ceramic waste replaced coarse and fine aggregates and cementitious materials in concrete mixtures. The results demonstrate that replacing 20% of coarse and 50% of fine aggregates with ceramic waste significantly enhances compressive strength, reaching 32.98 MPa and 35.83 MPa, respectively. Moreover, these replacements reduced carbon emissions during concrete production by 6–250 kg CO₂e/t, depending on the application. Introducing reinforcing fibers, such as carbon and Polyvinyl Alcohol (PVA) fibers, further improved concrete’s crack resistance, frost durability, and toughness under extreme conditions. These findings validate the feasibility of using ceramic waste as a sustainable alternative in construction materials, contributing to performance optimization and carbon reduction. The research offers new insights into eco-friendly concrete development aligned with the sustainable development goals (SDGs).
3D printing offers efficiency and design flexibility in construction, but its sustainability is limited by the carbon footprint of cement-based materials. In this sense, the present study proposes hybrid printable matrices with Portland cement (30%–50%), fine earth (50%–70%), and fly ash (0–10%). Hydration and rheology of pastes were analyzed using isothermal calorimetry, thermogravimetric analysis (TGA), and rheometry, while printable mortars were evaluated using a flow table, cone penetration, and uniaxial compression. Environmental performance was assessed through cradle-to-gate life cycle assessment (LCA). Cone penetration tests showed that increasing earth from 50% to 70% raises the structuration rate from 8.6 to 33.1 Pa/min, enhancing buildability but narrowing the open time. Fly ash mitigated this effect by reducing structuration and extending open time. In compression, increasing the mass fraction of earth from 50% to 70% reduced the strength from 19.2 MPa to 5.6 MPa. The mixture containing 60% earth and 10% fly ash achieved 10.7 MPa, showing improved strength at equivalent cement content. Regarding environmental impacts, the climate change potential decreased from 355.1 kg CO₂eq/m3 (50% earth, 50% cement) to 243.1 kg CO₂eq/m3 (60% earth, 30% cement, and 10% fly ash), 32% lower and below the 500–583 kg CO₂eq/m3 reported in the literature for printable mortars. These findings show the potential of earth–fly ash–cement hybrid matrices for eco-friendly, 3D printable mortars with balanced rheological, mechanical, and environmental performance.
Simultaneous localization and mapping (SLAM) is a crucial technology for construction robots, enabling complex environment mapping and localization at construction sites and facilitating autonomous construction. However, construction sites, particularly those of large public buildings, are characterized by complex spatial structures, time-varying conditions, and dynamic uncertainties. Achieving accurate SLAM in such environments is a highly challenging task for construction robots. In this paper, a SLAM dataset is created specifically for construction sites of large public buildings, and the performance of current mainstream open source 3D light detection and ranging (LiDAR) SLAM algorithms is evaluated. Firstly, an experimental platform for construction robots is established, and a SLAM dataset is generated by collecting data at the construction site of a large public building in Xi’an. Secondly, a simulation environment is developed based on the construction drawings of the ongoing project. A simulation model of the construction robot is created according to the experimental platform, and a SLAM dataset for the simulated construction site environment is compiled by data collection. Finally, comparative experiments involving ten types of open source 3D LiDAR SLAM algorithms are conducted, and the accuracy of SLAM pose estimation and point cloud maps is assessed. The experimental results offer valuable references for SLAM algorithm research for construction robots in construction site environments. Specifically, they reveal the strengths and limitations of existing algorithms under construction-specific challenges, guiding future algorithm optimization. This work not only bridges the gap in construction-oriented SLAM dataset resources but also promotes the practical application of autonomous construction robots in large public building projects.
The excellent mechanical properties of ultra-high performance concrete (UHPC) will reduce the cross-sectional size of UHPC beams, resulting in a decrease in the amount of UHPC and the carbon emission. However, the large amount of cement in UHPC can lead to significant carbon emissions during the production process. Few existing studies have paid attention to the relationship between the mechanical properties of UHPC beams and carbon emissions. In this study, a 30 m prestressed UHPC beam was taken as the research object. Based on the analysis of the actual force, a cross-section and reinforcement scheme considering its mechanical properties was formulated. The influence of material ratio and different design parameters on its bending moment capacity was then analyzed. Additionally, a carbon emission calculation model for the entire life cycle of the UHPC beam was constructed, and the carbon emissions of the 30 m UHPC beam under different material ratios were obtained. On this basis, the carbon strength of UHPC beams was introduced and analyzed. The results show that the structural carbon strength of the 30 m UHPC beam is better when the fiber volume fraction is 2%, the reinforcement ratio is 1.3%, and the UHPC compressive strength is between 140–160 MPa. In addition, a formula for calculating the structural carbon strength of the 30 m UHPC beam with different material ratios was obtained by machine learning. Through the formula, the carbon emissions in the entire life cycle of the 30 m UHPC beam after meeting the requirements of the bending moment capacity can be determined.
This study describes an environmental life cycle assessment (LCA), including an ecotoxicity analysis, of municipal solid waste incinerator bottom ash produced by a Portuguese waste-to-energy power plant. The LCA followed a “cradle-to-gate” (A1-A3) approach of the bottom ash production process itself and compares concrete mixes containing it with those using fly ash or Portland cement. The study uses site-specific data as input in the SimaPro software to evaluate the impacts associated with producing 1 tonne of bulk bottom ash at the plant’s exit gate. The results infer positive outcomes in all categories except natural resources depletion and renewable energy consumption: global warming potential decreased by 20% (–0.18 kg CO2eq) and non-renewable energy demand also improved with a 1 724 MJ reduction. These were attributed to waste treatment, especially recycling steel, aluminium, and ferrous and non-ferrous metals following sorting, which is a prerequisite for bottom ash processing. Applying these results to alkali-activated concrete mixes highlighted a 59% reduction in acidification potential and a 57% reduction in non-renewable energy use, despite a 442% increase in global warming potential compared with mixes using alternative binding agents. In the second part of the study, detailed chemical and biological analyses compared binders in bound and unbound forms. Ecotoxicity-related trials showed a shift from Class IV to Class III, with toxicity units for Daphnia magna decreasing by 89% when substituting cement with alkali-activated bottom ash, thereby demonstrating the material’s technical viability from an environmental hazard perspective.
Construction and demolition waste (CDW) is a low-carbon alternative to natural subgrade aggregates, which can alleviate the pressure of waste accumulation and resource exploitation. This study comprehensively analyzes the engineering properties, particle breakage mechanisms, and deformation behavior under environmental-loading effects of CDW as subgrade filler. CDW has both environmental and mechanical potential: it reduces solid waste landfilling and natural aggregate consumption, and its post-construction settlement after compaction is lower than that of traditional fillers. Even under the worst working conditions (brick aggregates with 96% compaction degree), its California bearing ratio (CBR) still reaches 21.6%. However, it has limitations such as a high abrasion value (up to 41%) and strong heterogeneity, requiring optimization through pretreatment (e.g., ball milling to remove mortar) and gradation control; CDW particle breakage occurs in three modes: fragmentation, abrasion, and grinding. Moderate breakage (controlling the proportion of 5–10 mm particles to 25%–30%) can fill voids and improve shear strength, while excessive breakage leads to strength attenuation. Breakage can be quantified using indices like breakage rate (Bg) and fractal dimension; CDW breakage and deformation are affected by internal and external factors. Among external factors, moisture content exceeding the optimum moisture content (OMC) increases permanent deformation by approximately 20%; each freeze–thaw (FT) cycle reduces the resilient modulus by 15%–25% (the modulus stabilizes after 10 cycles). Deformation of CDW subgrades is controlled by the environment-loading coupling effect, and existing constitutive models cannot fully capture the complex interactive effects of multiple factors.
To address the high construction difficulty and cost resulting from the heavy self-weight of concrete-filled steel tube (CFST) skeletons in the construction of long-span arch bridges, as well as the ineffective utilization of 0–3 mm waste fraction of sintered shale pottery sand —which leads to resource waste and environmental pollution when stockpiled—this study employed an experimental approach combining the close packing and over slurry theories to determine the optimal mix proportion for lightweight ultra-high performance concrete (LUHPC) incorporating 0–3 mm waste fraction of 800/700-grade sintered shale pottery sand. LUHPC exhibited excellent properties. With a volume fraction of 3% straight-round steel fibers, the compressive strength was 147.7 MPa, the tensile strength was 17.4 MPa, and the elastic modulus was 49.9 GPa. All groups achieved a slump flow of at least 220 mm, meeting the requirements for self-compacting. The apparent density ranged from 1.943 to 2.178 g/cm3, 22.2%–30.6% lower than that of ultra-high performance concrete (UHPC). Scanning electron microscope (SEM) analysis showed that the waste fraction of 800-grade sintered shale pottery sand provided better internal curing than that of 700-grade sand, thereby improving its mechanical performance. The addition of irregular steel fibers (end-hooked and wavy) enhanced tensile strength, but reduced flow properties and other mechanical properties. Analyses of carbon emissions and economics indicated that LUHPC with the waste fraction of 700- and 800-grade sintered shale pottery sand reduced emissions by 21.0% and 24.1%, and raw material costs by 42.9% and 45.0%, respectively, compared with conventional UHPC. Finally, a method integrating combined weighting and grey relational analysis was proposed to evaluate multiple performance criteria and select the optimal mix proportion, providing decision support for various engineering applications.
Marble powder (MP) and cement kiln dust (CKD) are important industrial by-products generated in large quantities, both with low recycling rates. Contrary to common utilization practices and research trends—such as using MP in plasters and assessing CKD as a supplementary cementitious material—this paper explores their potential use as inert fillers in self-compacting concrete (SCC). This approach, especially for CKD, offers more efficient recycling routes without compromising strength or durability. SCC mixtures of low environmental and economic cost were produced using MP and CKD as filler powder and metakaolin (MK) as a cement substitute (10% and 20% by mass). Each composition was evaluated for fresh properties, compressive strength, water permeability, and freeze–thaw (F-T) resistance. Mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM) were used to interpret these phenomena. Although CKD incorporation slightly increased strength, it reduced F-T resistance, while MK improved strength, permeability, and micromorphology, enhancing SCC’s durability.
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.