Search Results (41)

Reinforced concrete (RC) structures are susceptible to crack initiation and propagation during service, making accurate numerical simulation of crack behavior essential for assessing structural durability and safety. Current numerical approaches for simulating concrete cracking include smeared/continuum approaches, extended finite element method (XFEM), phase-field methods, and meso-mechanical models. In particular, smeared/continuum approaches (e.g., smeared crack and plastic-damage models such as CDP) indirectly reflect cracking through diffusive damage fields without providing explicit geometric information on crack locations and propagation paths. The XFEM module in commercial software is further restricted to first-order elements and encounters difficulties in simulating multi-crack propagation. These limitations indicate that further development of complementary crack-simulation frameworks is warranted. To this end, this paper presents a cracking simulation framework for RC members within the theoretical framework of the Specified Stress Method, adopting an adaptive degree-of-freedom strategy to balance computational accuracy and efficiency. The method introduces inelastic strain as an additional unknown and establishes a variational principle and the corresponding virtual work equation. Concrete cracking is described by specifying the stress on the crack plane to zero, so that the crack-surface stress remains zero after cracking, thereby avoiding the issue of damage reversibility and improving computational convergence. The method requires neither a predefined crack path nor remeshing after cracking. Unlike smeared/continuum approaches that rely on diffusive damage fields, the crack propagation paths, distribution characteristics, and evolution of multiple cracks are characterized through the spatial distribution of cracked integration points within the finite element mesh. In the present implementation, crack initiation is governed by the maximum tensile stress criterion, and a linear elastic constitutive model is adopted for concrete as a deliberate simplification to establish and verify the core computational mechanism of the framework. The proposed method was examined through three numerical examples. First, comparison with theoretical solutions confirmed the algorithm’s correctness in simulating cracking in heterogeneous RC tension members. Second, comparison with experimental results demonstrated qualitatively consistent crack propagation trends and load–displacement responses for RC beams under mixed-mode cracking; the calculated ultimate load of the plain concrete beam is lower than the experimental value, which is attributable to the use of the maximum tensile stress criterion without fracture energy considerations, and certain crack morphology deviations are observed due to the neglect of reinforcement–concrete bond-slip. Third, a multi-crack simulation of an under-reinforced RC beam showed that, whereas the XFEM module in ABAQUS captures only a single dominant crack near the mid-span, the proposed algorithm predicts multiple distributed cracking zones on both sides of the mid-span, qualitatively consistent with the typical flexural cracking behavior of under-reinforced RC beams; the algorithm also supports second-order elements (e.g., C3D20R) unavailable in the ABAQUS XFEM implementation. While the method is still in an exploratory stage, these results confirm the feasibility and potential of the Specified Stress Method as a complementary framework for RC cracking simulation, providing a basis for further development. Full article

To accurately predict temperature rise due to the concrete hydration heat released from the #0 segment of a continuous concrete girder bridge at an early construction stage for structural design purposes, researchers proposed an approach incorporating empirical predictive formulae with a preliminary numerical analysis. However, due to the uniqueness of the structural geometry and material in each engineering case and the limited data shared by the whole engineering community, no universal predictive empirical model for temperature rise due to hydration heat has yet been identified for practical use that can be applied to a variety of different projects. Moreover, the preliminary numerical analyses are usually based on questionable assumptions and simplifications of the physical truth, the accuracy of which also requires further validation. To this end, the present research measured the time-varying temperature samples of early age massive concrete in the #0 segment of Huangsha Harbor Bridge (a twin-deck three-span continuous concrete box girder bridge located in Jiangsu Province, China) and examined the accuracy of the predictive empirical models formulated by other researchers and the usability of a numerical modal established on a commercial finite element (FE) platform by comparing the corresponding results with the data from the present field measurements. The results suggest that the empirical formulae proposed can generally effectively describe the actual temperature distribution patterns related to the thermal issue, but they are characterized by inferior usability in some cases. In addition, the present comparison also indicates that the actual maximum temperature rise can be correctly predicted by the preliminary FE analysis in most cases. Full article

The Copenhagen 10-step method is a set of policies that originated in the 1950s to reduce vehicle traffic in Copenhagen, which was heavily impacted by traffic. These policies are incorporated into a different dynamic on a global scale every day and are adopted while maintaining relevance. These policies, advocated in the context of climate change and carbon emission targets, as well as livability and health-focused urbanization, justice, and accessibility in transportation, are criticized for potentially negatively affecting low-income groups and commercializing urban transformation. Furthermore, they require adaptation because their applicability is seen as limited in terms of localization. In this context, the adaptability of the method to different social and spatial contexts has become a critical research topic, particularly in local studies, where application is more important and the order of implementation becomes of great importance. Within the scope of this study, a Copenhagen 10-step prioritization study was conducted specifically for the Küçükçekmece Kanarya Neighborhood, where low-to-middle socioeconomic groups live, and which has been declared a risky area in terms of building stock. Accordingly, a two-phase study was conducted. In the first phase, transportation and planning experts were asked to prioritize the 10 steps, and the timing of each implementation was determined based on the resulting ranking. In the second phase, accessibility analyses for the region were conducted using GIS (Geographical Information Systems)-based spatial data, such as accessibility, slope, and the distribution of urban facilities. Subsequently, these two phases were combined to create a simple prioritization framework for the areas of greatest concern in Kanarya, as well as for urban renewal, transportation, and government investment plans. According to the SWARA results, increasing bicycle use (C10) was the most important criterion at 17.2%, followed by making the bicycle the primary mode of transportation (C9) at 13.8% and adapting the city to seasonal changes (C8) at 11.5%. This study, which is significant for its focus on a specific region at the local implementation level, presents a straightforward model—based on concrete findings—for prioritizing sustainable transportation and urbanization policies in socioeconomically vulnerable areas. In doing so, it contributes to aligning theoretical approaches with practical field applications. Full article

The clinker grinding stage in Portland cement production is highly energy-intensive, primarily due to particle agglomeration and intensified interparticle attractive forces that hinder efficient comminution. Grinding aids (GAs) are routinely employed to mitigate these issues, enhancing grinding efficiency and improving cement performance. However, the undesirable side effects associated with conventional GAs on cementitious systems have spurred interest in modification strategies that can concurrently optimize grinding efficiency and final product quality. In this study, widely used commercial GAs, triisopropanolamine (TIPA), diisopropanolamine (DEIPA), and diethylene glycol (DEG), were chemically modified via esterification with organic acids of different carbon chain lengths. Cement specimens incorporating these modified GAs were produced at two dosages (0.05% and 0.1% by mass of clinker + gypsum), resulting in 24 distinct Portland cement formulations alongside a control mix. The influence of modification on grinding efficiency, particle size distribution (PSD), and powder flowability was investigated. Furthermore, scanning electron microscopy (SEM) was utilized to analyze particle morphology and concrete microstructural characteristics with powder flow behavior. The results indicate that organic acid modification not only facilitates achieving target fineness with lower energy consumption but also markedly improves both the PSD profile and the powder’s flow properties. Specifically, hexanoic acid-modified TIPA and DEIPA, along with propanoic acid-modified DEG, delivered the most favorable outcomes across the evaluated parameters. These findings underscore the potential of developing next-generation, modified GAs that simultaneously enhance energy efficiency and powder handling in cement grinding operations. Full article

The use of cementless concrete (geopolymer concrete (GPC)) incorporating fly ash and bundled steel fibers to produce full-scale precast concrete pipes is an economical, viable and sustainable solution for sewer infrastructure for decreasing the overall carbon impacts. This research explores the mechanical behavior of precast full-scale pipes (450 mm inner diameter) incorporating cementless concrete and bundled steel fibers. The GPC mixture was produced by completely substituting cement with fly ash generated by the local coal power plant. The bundled steel fibers were locally manufactured from long wires. The proportions investigated of the bundled steel fibers in the GPC pipes were 20 and 40 kg/m³. A total of six full-scale GPC pipes and two conventional cement concrete pipes were cast in a commercial precast pipe unit. The crushing strength under external load was evaluated using the three-edge bearing test (TEBT) on the pipes without fibers, showing comparable cracking and ultimate loads of GPC pipes and conventional cement concrete pipes. Both types of pipes satisfied the strength requirement of ASTM C76 class III. The use of bundled steel fibers in GPC pipes improved the cracking and ultimate loads by 18% and 22%, respectively, when 40 kg/m³ of bundled steel fibers were added. This upgraded the ASTM C76 strength class from class III to IV due to the improved crack resistance and ultimate load. Conventional cement concrete pipes and GPC pipes exhibited similar cracks at the critical regions (springlines, invert and crown). However, GPC pipes with bundled steel fibers showed a well distributed pattern of multiple secondary cracks along the longitudinal axis of the pipes. The final failure was governed by the flexure action and radial tension in the tested pipes. The economic analysis of cement concrete and GPC pipes showed comparable costs. However, the incorporation of fibers increased the cost of GPC pipes due to the limited local availability of proprietary fibers. This study highlights a new horizon of GPC for the manufacturing of sustainable and economical precast pipes as an environmentally friendly substitute to conventional cement concrete pipes for sustainable sewer infrastructure and adds novelty to the current state-of-the-art knowledge. Full article

The contribution of members of the agri-food system to achieving the Sustainable Development Goals is a key element in the global transition to sustainable development. The use of sustainable management systems supports the development of an integrated approach with a spirit of continuous improvement. Such organization is based on risk-management tools that are applied to multiple stakeholders, e.g., those responsible for product quality, occupational health and safety, and environmental impact, thus enabling better global performance. In this review, the term “ethical food systems” is used in our discussion of the concrete methods that can be used to endorse fairness and concern across the food chain. This comprises safeguarding equitable access to nutritious foods, defending animal welfare, assisting ecologically accountable production, and addressing social and labor justice within supply chains. Ethical factors also include transparency, cultural respect, and intergenerational responsibility. Consequently, the objective of this review is to address how these ethical values can be implemented within a One Health framework, predominantly by assimilating plant-based diets, developing governance tools, and resolving nutritional insecurity. Within the One Health framework, decoding ethical principles into practice necessitates a set of concrete interventions: (i) raising awareness of animal rights; (ii) distributing nutritional and environmental knowledge; (iii) endorsing plant-based food research, commercialization, and consumption; (iv) development of social inclusion and positive recognition of vegan/vegetarian identity. At the same time, it should be noted that this perspective represents only one side of the coin, as many populations continue to consume meat and rely on animal proteins for their nutritional value; thus, the role and benefits of meat and other animal-derived foods must also be recognized and discussed. This operational definition provides a foundation for asking how ethical perspectives can be applied. A case study from Africa shows the implementation of a sustainable and healthy future through the One Health approach. Full article

Textile-reinforced concrete (TRC) is an alternative class of mechanical reinforcement for cement composites. The biaxial braided reinforcement structure in composite materials with diverse cross-sectional shapes offers high adaptability, torsional stability, and resistance to damage. In general, 3D textile reinforcements improve the mechanical properties of composites compared to 2D reinforcements. This study aimed to verify reinforcement behavior by comparing multidimensional braided textiles, 2D (one- and two-layer) reinforcements, and 3D reinforcement in composite cementitious boards. Experimental tests were performed to evaluate the effect of textile structures on cementitious composites using four-point bending tests, porosity measurements, and crack patterns. All textiles showed sufficient space between yarns, allowing the matrix (a commercial formulation) to infiltrate and influence the composite mechanical properties. All composites presented ductility behavior. The two layers of 2D textile composites displayed thicker cracks, influenced by shear forces. Three-dimensional textiles exhibited superior values in four-point bending tests for modulus of rupture (7.4 ± 0.5 MPa) and specific energy (5.7 ± 0.3 kJ/m²). No delamination or debonding failure was observed in the boards after the bending tests. The 3D textile structure offers a larger contact area with the cementitious matrix and creates a continuous network, enabling more uniform force distribution in all directions. Full article

Historic districts, as important spatial units that carry urban cultural memory and everyday social life, play a crucial role in shaping residents’ spatial identity, emotional attachment, and perceptual experience. Although quantitative research on built environments and perception has advanced considerably in recent years, the mechanisms through which perception is formed in historic districts, particularly the nonlinear threshold effects and perceptual trade-off patterns that arise under conditions of high-density and mixed land use, remain insufficiently examined. To address this gap, this study develops an analytical framework that integrates spatial attributes with multidimensional subjective perceptions. Focusing on six historic districts in central Shanghai, the study combines micro-scale environmental indicators extracted from street-view imagery, POI data, and public perceptual evaluations and employs an XGBoost model to identify the nonlinear response patterns, threshold effects, and perceptual trade-offs across seven perceptual dimensions. The results show that natural elements such as visual greenery and sky openness generate significant threshold-based enhancement effects, and once reaching a certain level of visibility, they substantially increase positive perceptions including beauty, safety, and cleanliness. By contrast, commercial and traffic-related facilities exhibit dual and competing perceptual influences. Moderate densities enhance liveliness, whereas high concentrations tend to induce perceptual fatigue and intensify negative emotional responses. Overall, perceptual quality in historic districts does not arise from linear accumulation but is shaped by dynamic perceptual trade-offs among natural features, functional elements, and cultural symbolism. Overall, the study reveals the coupling mechanism between spatial renewal and perceptual experience amid the pressures of urban modernization. It also demonstrates that increasing visible greenery (e.g., planting street trees, incorporating micro-green spaces, improving façade greening), enhancing street openness (e.g., optimizing view corridors, reducing visual obstruction, implementing moderate setback adjustments), guiding a moderate mix and spatial distribution of commercial and service functions, and strengthening the perceptibility of cultural landscape elements (e.g., façade restoration, streetscape coordination, and improved signage systems) are concrete and effective planning and design actions for improving landscape quality and enhancing the experiential quality of historic districts. Full article

This study investigates an alternative methodology for incorporating polymeric and steel fibers into concrete. Conventional reinforcement approaches often require complex application techniques and face industrial limitations. In contrast, the present work evaluates the use of short, discontinuous fibers—commercial polypropylene fibers (PFRC), polypropylene fiber braid (PFBRC) and steel fibers (SFRC)—which enable improved dispersion, ease of mixing and potential mechanical benefits. The fibers were randomly oriented and evenly distributed within the cementitious matrix. Mechanical performance was assessed through four-point bending tests combined with displacement measurements, acoustic emission analysis and uniaxial compression tests, while scanning electron microscopy (SEM) confirmed fiber–matrix interaction and fragment retention. The results demonstrated significant improvements, with compressive strength exceeding that of unreinforced concrete, while hybrid fiber systems provided enhanced crack resistance and post-cracking stability. Overall, the findings highlight that the integration of discontinuous fibers may provide tangible mechanical advantages, potentially outweighing the structural benefits of continuous reinforcing bars in applications requiring high strength and reliable mechanical performance. Full article

Conventional characterization of ultrasonic testing (UT) transducers primarily focuses on determining centre frequency and usable bandwidth. However, the relative amplitude distribution across different frequency components—particularly in low-frequency transducers used for civil engineering applications—remains largely overlooked. This paper introduces a comprehensive methodology to assess the influence of transducer coupling and specimen geometry on ultrasonic pulse velocity signals. The novel approach combines high-frequency laser Doppler vibrometry, real-time photoelastic imaging, and computer simulations using commercial semi-analytical wave-propagation software. The methodology is applied to the characterization of a 250 kHz UT transducer, with particular emphasis on how coupling with a solid test medium alters its frequency response. A glass specimen with an acoustic impedance comparable to that of concrete is used to simulate practical testing conditions. Vibration patterns recorded at the distal end of the specimen are analysed through computer simulations and validated experimentally using a novel photoelastic system capable of capturing wave–specimen interactions at ultrasonic frequencies in real time. The findings offer valuable insights into frequency-dependent signal behaviour and transducer–medium interactions, providing practical guidance for the design and optimization of UT inspections in concrete and other highly attenuative materials commonly encountered in civil engineering. Full article

Lumped plasticity models available in commercial software offer a limited resolution of damage distribution along structural members. This study presents an open-source workflow that combines force-based fiber elements in OpenSeesPy with automated 3D post-processing for visualizing distributed plasticity in reinforced concrete piles. A 60 cm diameter pile subjected to monotonic lateral loading is analyzed using both SAP2000’s default plastic hinges and OpenSeesPy fiber sections (Concrete02/Steel02). Although the fiber model incurs a runtime approximately 2.5 times greater, it captures the gradual spread of yielding and deterioration with improved fidelity. The presented workflow includes Python routines for interactive stress–strain visualization, facilitating the identification of critical sections and verification of strain limits. This approach offers a computationally feasible alternative for performance-based analysis with enhanced insight into member-level behavior. Because the entire workflow—from model definition through post-processing—is fully scripted in Python, any change to geometry, materials, or loading can be re-run in seconds, dramatically reducing the time taken to execute sensitivity analyses. Full article

This study examines the pore structure and distribution in 3D printed and cast foamed concrete using protein-based and synthetic foaming agents alongside various stabilizing additives. In 3D printed samples, pores are irregular and flattened due to mechanical forces during printing, whereas cast samples display uniform, spherical pores from homogeneous foam distribution. Samples containing the CA stabilizer show higher apparent densities (up to 2.05 g/cm³ for printed samples), correlating with lower water absorption. Protein-based foaming agents (PS) produce smaller, more evenly distributed pores, while synthetic agents (AS) result in larger, less uniform pores. Stabilizers significantly influence pore characteristics: commercial stabilizers yield smaller, more uniform pores, while recycled industrial oil (UO) leads to larger, more variable pores. Protein-based agents improve structural stability and reduce water absorption through uniform pore distributions, while synthetic agents lower density and increase water absorption. The highest sorption values were observed in samples with AS without stabilizer (1.7 kg/m²h¹/²) and AS and UO (1.6 kg/m²h¹/²) in a vertical orientation, with the horizontal orientation of sample AS and UO achieving a peak value of 2.0 kg/m²h¹/². Moreover, stabilization using UO resulted in higher sorption coefficients than stabilization with CA. High porosity in M1 resulted in low strength (0.2 MPa bending, 0.1 MPa perpendicular compression), while M5 showed superior performance (11.5 MPa perpendicular compression). PS-foamed samples (M4, M6) with uniform pores had the highest strengths, with M6 achieving 3.8 MPa bending and 10.3 MPa perpendicular compression. Perpendicular compression (M5: 11.5 MPa) was up to three times stronger than parallel compression due to weak interlayer bonds in 3D printing. Full article

Developing environmentally friendly bulk materials capable of easily and thoroughly removing trace amounts of dye pollutants from water to rapidly obtain clean water has always been a goal pursued by researchers. Herein, a green material with a 3D architecture and with strong underwater rebounding and fatigue resistance ability was prepared by means of the assembly of biopolymer chitosan (CS) and natural caraganate fibers (CKFs) under freezing conditions. The CKFs can randomly and uniformly distribute in the lamellar structure formed during the freezing process of CS and CKFs, playing a role similar to that of “steel bars” in concrete, thus providing longitudinal support for the 3D-architecture material. The 2D layers formed by CS and CKFs as the main basic units can provide the material with a higher strength. The 3D-architecture material can bear the compressive force of a weight underwater for multiple cycles, meeting the requirements for water purification. The underwater compression test shows that the 3D-architecture material can quickly rebound to its original shape after removing the stress. This 3D-architecture material can be used to purify dye-containing water. When its dosage is 3 g/L, the material can remove 99.65% of the Congo Red (CR) in a 50 mg/L dye solution. The adsorption performance of the 3D architecture adsorbent for CR removal in actual water samples (i.e., tap water, seawater) is superior than that of commercial activated carbon. Due to its porous block characteristics, this material can be used for the continuous and efficient treatment of wastewater containing trace amounts of CR dye to obtain pure clean water, meaning that it has great potential for the effective purification of dye wastewater. Full article

This research was conducted to analyse the possibility of using raw, untreated recycled tyre fibres as an effective concrete reinforcement according to circular economy principles. The aim of the article was also to develop a method for dispensing tire fibres on a real scale. Additional treatment and homogenisation of recycled steel fibres entail higher energy consumption, emissions of greenhouse gases, and increased costs. However, obtaining durable and safe concrete effectively reinforced with steel fibres is critical. Finding a balance between environmental friendliness and product durability is a circular economic challenge. Reference concrete with commercial steel fibres (15 kg/m³) and two concretes containing various quantities of non-treated, raw tyre recycled fibres (25 kg/m³ and 45 kg/m³) were industrially produced. Tests were carried out on the properties of the concrete mixture and hardened concrete, such as compressive strength, flexural strength, splitting strength, modulus of elasticity, residual flexural tensile strength, and fibre distribution in concrete. Tests revealed that increasing the amount of raw tyre fibres disturbs the structure and causes air entrainment and the formation of fibre clusters. Smaller quantities of raw tyre fibres turn out an effective concrete reinforcement. The use of non-treated tyre fibres as concrete reinforcement is possible but requires more stringent control of the concrete parameters. Implementation tests on an industrial scale are a novelty in this study, presenting an analysis of the possible dispensing of tyre fibres in a ready-mixed concrete production plant and testing the characteristics of manufactured concrete. Full article

In order to achieve low-carbon optimization in the intelligent mix ratio design of concrete materials, this work first constructs a concrete mix ratio database and performs a statistical characteristics analysis. Secondly, it employs a standard back propagation (BP) and a genetic algorithm-improved BP (GA-BP) to predict the concrete mix ratio. The NSGA-II algorithm is then used to optimize the mix ratio. Finally, the method’s accuracy is validated through experiments. The study’s results indicate that the statistical characteristics of the concrete mix ratio data show a wide distribution range and good representativeness. Compared to the standard BP, the fitting accuracies of each GA-BP set are improved by 4.9%, 0.3%, 16.7%, and 4.6%, respectively. According to the Fast Non-Dominated Sorting Genetic Algorithm II (NSGA-II) optimization for meeting C50 concrete strength requirements, the optimal concrete mix ratio is as follows: cement 331.3 kg/m³, sand 639.4 kg/m³, stone 1039 kg/m³, fly ash 56 kg/m³, water 153 kg/m³, and water-reducing agent 0.632 kg/m³. The 28-day compressive strength, material cost, and carbon emissions show relative errors of 2.1%, 0.6%, and 2.9%, respectively. Compared with commercial concrete of the same strength grade, costs and carbon emissions are reduced by 7.2% and 15.9%, respectively. The methodology used in this study not only significantly improves the accuracy of concrete design but also considers the carbon emissions involved in the concrete preparation process, reflecting the strength, economic, and environmental impacts of material design. Practitioners are encouraged to explore integrated low-carbon research that spans from material selection to structural optimization. Full article