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•Nano calcium carbonate and ethyl cellulose protective film were coated on polypropylene fibers.•Fiber pullout friction and pH-responsive protective film exposes nano calcium ...carbonate coating once cracked.•Nano calcite facilitates calcium carbonate precipitation and further hydration within cracks.•Autonomic healing performance of cracked mortar is enhanced due to fiber modification.
Fibers can enhance self-healing of concrete by restricting crack propagation and supplying nucleation sites in cracks. To further improve the self-healing effect of fiber concrete, a new strategy of fiber modification for self-healing is proposed herein. In this study, polypropylene (PP) fibers were coated with nano calcium carbonate as nano seedings and ethyl cellulose film as a protective layer. The protective layer can inhibit the interactions of coated nano seedings with cement matrix before cracking. While after mortar mixing and cracking, the protective layer was gradually removed due to shear stress in mixing and friction during fiber pull-out in cracking processes, respectively. With the elimination of the protective layer, the remaining nano calcium carbonate coating at around 5.6 % of fiber mass could be exposed to cracks, thereby accelerating healing product generations by hydration and calcium carbonate precipitation, which was verified by scanning electron microscopic observations, Fourier-transform infrared spectroscopy and thermogravimetry analysis. Owing to the effects of modified fibers, closure of 300–500 μm wide cracks was enhanced and 100 % recovery of water tightness was subsequently achieved.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•A systematical review of 3D printable cementitious materials was conducted.•A multi-level material design (MMD) for development of 3DPCM was proposed.•MMD is illustrated via inter-connected ...pyramids, i.e. material, printing & structure.•Based on MMD, three different levels of material design are reviewed successively.
3D printing, or additive manufacturing, is a technology which adopts layer-by-layer additive deposition process to build three-dimensional objects. Over the past decade, 3D printing has been attracting more and more attention in the building and construction industry. Compared with conventional concrete casting techniques, 3D printing contributes to higher efficiency with freeform construction, greatly reduced labor and much less construction waste. However, 3D printable cementitious materials are different from conventional concrete in terms of rheology, printability, and mechanical performances. This paper aims to systematically bridge the gap between the requirement and research and development of 3D printable cementitious materials to date. Guided by 3D printing process and multi-level design of cementitious materials, the requirements for 3D printable cementitious material at different material development levels are discussed. This paper provides insights for the future development of 3D printable cementitious materials for building and construction by controlling the basic inputs of materials to obtain desired structural performance.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Obstacles can play a prominent role in evacuations from spaces like classrooms. This study investigates the impact of two types of human-obstacle interactions on evacuations, including ...passing-over-obstacles and pushing-obstacles. A modified cellular automata model was adopted which considers the influence of exits and aisles, local density, and personality traits. Calibrated with a real-world evacuation video, this model enabled the simulation of passing-over-obstacle behavior. Parametric analyses were then conducted testing various geometrical layouts and behavioral features in the context of both traditional classrooms and active learning classrooms. Results showed that (1) human-obstacle interaction has a substantial impact on evacuation when exit capacity is less restrictive; (2) the passing-over-obstacle behavior can be advantageous for evacuation efficiency, opposite to the pushing-obstacle behavior; (3) interplay between the two types of interactions is conspicuous when the frequency of pushing-obstacle behavior is high; (4) appropriate geometrical design could make the evacuation process more robust to disadvantageous effects of the pushing-obstacle behavior; (5) proper evacuation management can make the best of pedestrians' advantageous passing-over-obstacle behavior. Accordingly, we propose several strategies for evacuation management practices. This includes setting aisles beside walls, encouraging appropriate passing-over-obstacle behavior in the front of or near the walls in traditional classrooms, discouraging pushing-obstacle behavior and leaving enough space near the exit regions in active learning classrooms.
•Two types of human-obstacle interactions are studied: passing-over obstacles and pushing obstacles.•The proposed model is calibrated with a real-world video, demonstrating good agreement and reproducibility.•The two types of interactions show opposite impacts on evacuation, and their interplay is identified.•Bifurcate effect of each type of interaction is found to depend on the geometrical design.•“Behavior-oriented” strategies on evacuation management are proposed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Factorial design was adopted to evaluate influence of five variables on material rheological properties.•Empirical models were established to predict rheological properties and were verified by ...experiment.•Increased fiber dosage boosts all rheological parameters, while water-to-binder ratio shows opposite trend.•Torque viscosity increases while flow resistance and thixotropy decrease with fly ash-to-cement ratio.•Silica fume-to-cement ratio shows an opposite trend as compared to that of fly ash-to-cement ratio.
3D printable construction materials need to be conveyed through a delivery system whilst possess certain flow resistance to ensure materials can sustain the weight of subsequent layers. To meet these requirements, material rheological properties should be optimized. In this study, factorial design was adopted to evaluate the influences of five variables (water-to-binder ratio, sand-to-binder ratio, fly ash-to-cement ratio, silica fume-to-cement ratio, and dosage of fiber) on material rheological properties (flow resistance, torque viscosity and thixotropy). Empirical models were established to predict rheological properties and were verified by experiment. Results imply that the increment of the dosage of fiber boosts all the rheological parameters, which are declined with the increment of water-to-binder ratio. Torque viscosity raises while flow resistance and thixotropy are decreased with the rise of fly ash-to-cement ratio. Conversely, the influence of silica fume-to-cement ratio shows an opposite trend on rheological properties as compared to that of fly ash-to-cement ratio. Flow resistance and torque viscosity are improved whilst thixotropy is declined if sand-to-binder ratio increases. Different formulations were adopted in printing test for verification and demonstration purpose via a robotic arm printing system in the end.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
In the past decades, incorporating crumb rubber into concrete has attracted attention in the field of building materials due to the properties improvement it brought. In this study, crumb rubber of ...two particle sizes (40CR and 80CR, which have a sieve size of 400 μm and 220μm, respectively) is incorporated into engineering cementitious composite (ECC) material to replace silica sand. Furthermore, three different replacement percentages (0, 15%, 25% by volume) for each crumb rubber size are conducted in this study. The influence of crumb rubber on the ECC is revealed via density, compressive strength, flexural performance, drying shrinkage, restrained shrinkage and environment footprint. The experimental results show that the incorporation of crumb rubber into ECC increases bending deformation capacity, decrease density and compressive strength. While the free drying shrinkage of ECC increases with the addition of crumb rubber, lesser crack number, crack width and cracking tendency were found in the restrained ring test when compared to ECC without crumb rubber. In terms of crumb rubber size, ECC with smaller crumb rubber appear to have lower density and higher bending defamation capacity and shrinkage than those with larger crumb rubber. In addition, incorporating crumb rubber into ECC reduces CO2 emission, thus improve the greenness of ECC to a certain degree.
Knowledge of evacuees' movement dynamics is crucial to building safety design and evacuation management. Although it is recognized that stepwise movement is the fundamental element to construct the ...whole evacuation process, movement pattern and its influencing factors are still not well understood. In this study, we explored the potential of adopting machine learning methods to study evacuees' stepwise movement1 dynamics based on two videos of quasi-emergency evacuation experiments. The movement patterns were categorized through Two-step Cluster Analysis and principal influencing factors were identified through Principal Component Analysis. The relationship between the movement patterns and the principal components were investigated using different modeling methods: traditional method (Multinomial Logit Model, MLM) and machine learning methods (Decision Tree, Support Vector Machine, K-Nearest Neighbor, and Artificial Neural Network). Results from two experimental videos showed reasonable consistency and the main findings are: (1) Distance to the target exit has the most pronounced effect on a single evacuee's stepwise movement pattern. (2) Surrounding evacuees' actions also have significant and complex influence on a single evacuee's stepwise movement pattern. (3) MLM showed comparable prediction accuracy with machine learning methods when the scenario is simple. The superiority of machine learning became apparent when the scenario was more complex, with a maximum enhancement of 13.25% in prediction accuracy. Each machine learning method demonstrated distinct features and advantages in different aspects.
•A less biased analytical methodology is proposed to study movement dynamics from microscopic perspective.•Evacuees' movement patterns during evacuation and principal influencing factors were extracted from two experimental videos.•Classification performances of four machine learning methods and Multinomial Logit Model were compared.•Distance to the target exit and surrounding evacuees' actions can affect individual evacuee's movement pattern.•Surrounding evacuees' direction-changing action negatively influences individual evacuee's evacuation speed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Healable crack widths of cementitious composites are still at micro scale currently, even after specific self-healing agents like bacteria are incorporated. To enlarge the size of healable cracks to ...macro scale (> 1 mm), in-situ gelation strategy was adopted to develop self-sealing concrete herein. This strategy was achieved by encapsulating sodium alginate which could be released then react with calcium ions to in-situ generate calcium alginate hydrogels within cracks. The characteristics of capsules were investigated, and results revealed that these capsules could endure shear stress during mixing of cementitious composites, rupture when composite cracked and subsequently induce in-situ gelation. Owing to the characteristics of capsules, mortar specimens with the capsules obtained self-sealing capacity for macro cracks. The crack sealing of cementitious composites with capsules was further simulated based on the volume growth kinetics of hydrogels and stereology. The simulation results were generally consistent with the experimental results in this study. To sum up, the experimental and modelling explorations suggested a great potential of macro-scale self-sealing of cracks in cementitious composites via in-situ gelation.
This paper studies the photocatalytic performance of graphene-based titanium dioxide (TiO2) on cementitious composites for the decomposition of Escherichia coli (E. coli) under visible light. ...Graphene-based TiO2 was first synthesized through a hydrothermal process. The composites were then evaluated in terms of adsorption capability and degradation of methylene blue dyes. The adsorption test shows a remarkable increase in the amount of dye adsorbed into the composite surface. GO-P25 could adsorb around 60% of the initial dye, while less than 10% of the initial dye was adsorbed by pristine TiO2-P25. The synthesized graphene-based TiO2 significantly enhanced the dye degradation activity (94%) compared to pristine P25 (36%) and Krono (52%), even with the longer irradiation time for P25 and Krono. This led to an increase in reaction rate that was almost 20 times that of P25. Considering the good adsorption capabilities and high photodegradation of dye under visible light for GO-P25, cement-based surfaces containing GO-P25 are expected to be improved for the decomposition of Escherichia coli (E. coli) under visible light. Graphene-based TiO2 on a cement-based surface showed high antibacterial activity with a 77% reduction in number of bacteria compared to a cement-based surface containing pristine TiO2. This study confirms the effectiveness of the composites for disinfection of E. coli under visible light.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
•We investigate fiber reinforcing effect on asphalt binder under low temperature.•Fiber pullout strength can exceed fiber strength due to asphalt coating effect.•Aramid fiber needs longer embedment ...length to develop bond than polyester fiber.•Addition of polyester fiber can greatly enhance failure tensile strain of asphalt.•Fiber reinforced asphalt mains its tensile ductility with decreasing temperature.
This research examines reinforcing effect of different fibers on asphalt binder under low temperature. Laboratory test of multiple-fiber pullout (MFPT) from asphalt matrix was conducted to investigate the influence of fibers (fiber type and embedment length) and matrix (asphalt binder type) on the fiber pullout strength. Furthermore, the influence of fiber (with or without fiber, fiber length and dosage) and matrix (asphalt binder type and temperature) on the tensile properties of fiber reinforced asphalt (FRA) binder was investigated via direct tensile test (DTT). From the MFPT test it was found that fiber pullout strength can actually exceed the fiber strength provided by the manufacturer, presumably due to coating effect of the asphalt on the surface of fibers. Aramid fiber requires much longer embedment length to fully activate its bond with asphalt than the polyester fiber does. From the DTT test it was observed that addition of adequate polyester fiber can greatly enhance the tensile properties of the FRA, particularly in terms of failure tensile strain. While asphalt matrix becomes more brittle when temperature drops, FRA mains its tensile ductility with decreasing temperature, which deserves further investigation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Recognizing the importance of building-specific social impact assessment tools to the achievement of social sustainability of building projects, this study developed a methodological framework for ...social life cycle assessment of buildings through stakeholder-based approach, which includes the following four parts. (1) An assessment framework was proposed considering four stakeholders, including worker, occupant, local community and society, and impact subcategories associated with different social concerns; (2) Indicators were selected for each subcategory based on the assessment objective and data availability. They were categorized into three groups, including quantitative indicators in generic analysis, as well as quantitative and semi-quantitative indicators in site-specific analysis, and corresponding scoring method were provided; (3) Weights among impact subcategories were generated through questionnaire survey based on analytic hierarchy process method, and weights among life-cycle phases were determined considering the possibility to place control as well as level of concern of construction practitioners; (4) The proposed method was applied to a case study comparing two buildings with different construction methods, namely prefabricated prefinished volumetric construction (PPVC) project and semi-prefabrication project. The result suggests that PPVC project outperforms semi-prefabrication one in terms of life-cycle social performance. This is mainly caused by its capability to protect worker's health and safety as well as its contribution to technology development.
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•Propose a method for building-specific social life cycle assessment.•Construct a stakeholder-based assessment framework for building evaluation.•Define three types of indicators with corresponding scoring methods.•Apply this method to compare modular and semi-prefabricated construction projects.•Modular construction project outperforms in life-cycle social performance.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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