Search Results (112)

Alkali-activated building materials have attracted the interest of many researchers due to their low cost and eco-efficiency. Different binders with different chemical compositions can be used for their production, so the reaction mechanism can become complex and the results of studies can vary widely. In this work, several alkali-activated mortars based on marginal by-products as binders, such as high calcium fly ash and ladle furnace slag, are investigated. Their mechanical (flexural and compressive strength, ultrasonic pulse velocity, and modulus of elasticity) and physical (porosity, absorption, specific gravity, and pH) properties were determined. After evaluating the mechanical performance of the mortars, the optimum mixture containing fly ash, which reached 15 MPa under compression at 90 days, was selected for the production of precast compressed slabs. Steel or glass fibers were also incorporated to improve their ductility. To reduce the density of the slabs, 60% of the siliceous sand aggregate was also replaced with recycled polyethylene terephthalate (PET) plastic aggregate. The homogeneity, density, porosity, and capillary absorption of the slabs were measured, as well as their flexural strength and fracture energy. The results showed that alkali activation can be used to improve the mechanical properties of weak secondary binders such as ladle furnace slag and hydrated fly ash. The incorporation of recycled PET aggregates produced slabs that could be classified as lightweight, with similar porosity and capillary absorption values, and over 65% achieved strength compared to the normal weight slabs. Full article

A new concept of a 3D volumetric module, made up of six plane stiffened self-compacting fiber-reinforced concrete (SFRC) panels, is here studied. Experimental campaigns are carried out on SFRC material and on the thin-slab structures used for this modular concept. The high volume of steel fibers (80 kg/m³) used in the formulation of this concrete allow a positive strain hardening to be obtained in the post-cracking regime observed on the bending characterization tests. The high mechanical material characteristics, obtained both in tension and compression, allow a significant decrease in the module slabs’ thickness. The tests carried out on the 7 cm thick slab demonstrate a high load-bearing capacity and ductility under bending loading; this is also the case for shear loading configuration, although without any shear reinforcements. Numerical simulations of the material mechanical tests were conducted using Abaqus code; the results corroborate the experimental findings. Then, simulations were also conducted at the structural level, mainly to evaluate the behavior and the bearing capacity of the thin 3D module stiffened slabs. Finally, knowing that the concrete module truck transport can be a weak point, the decelerations induced during transportation were characterized and the integrity of the largest 3D module was demonstrated. Full article

Cracks and concentrated stresses can develop in precast concrete slabs, depending on the quality of the joints. The open-type joint method was adopted herein to fabricate a full-scale precast concrete slab joint. The open-type joint method features an exposed joint configuration that allows for direct installation of shear connectors without temporary formwork, improving constructability and load transfer efficiency. Full-scale load testing was carried out using a four-point loading experiment, revealing that the precast concrete slab had a yield load of 550 kN and maximum load of 733 kN. A slab using the cast-in-place method was measured to have a yield load of 500 kN and maximum load of 710 kN. A finite element analysis (FEA) model modeled the precast concrete slab, and the displacement and maximum load were analyzed. The FEA showed a maximum error within 7%. Therefore, the FEA results can predict the structural performance of the load–displacement of the precast concrete slab. The support vector regression model predicted key structural performance indicators such as concrete compressive strength, maximum load, displacement, and principal stress. The prediction results indicated that the average error converged within 3%. The prediction results of the SVR model can complement FEA by estimating outcomes without the need for complex modeling. Thus, the precast concrete slab using the open-type joint method was able to achieve structural performance equivalent to that of the slab using the cast-in-place technique. Furthermore, FEA and machine learning will be able to predict the structural performance of precast concrete slabs using the open-type joint method. Full article

Under the impetus of achieving global sustainable development goals, the civil construction industry is accelerating its transition towards high-quality, green, and low-carbon practices. Prefabricated, modular building technology has become a key tool due to its advantages in energy conservation, emission reduction, and shortened construction periods. However, existing research on the seismic performance of prefabricated, modular, reinforced concrete column–beam (RCS) composite structures often focuses on the construction form of beam–column joints, paying less attention to the impact of floor slabs on the seismic performance of joints during earthquakes. This may make joints a weak link in structural systems’ seismic performance. To address this issue, this paper designs a prefabricated, modular RCS composite joint considering the effect of floor slabs and uses the finite element software ABAQUS 2023 to perform a quasi-static analysis of the joint. The reliability of the method is verified through comparisons with the experimental data. This study examines various aspects, including the joint design and the material’s constitutive relationship settings, focusing on the influence of parameters, such as the axial compression ratio and floor slab concrete strength, on the joint seismic performance. It concludes that the seismic performance of the prefabricated, modular RCS composite joints considering the effect of floor slabs is significantly improved. Considering the composite effect of the slabs, the yield loads in the positive and negative directions for node FJD-0 increased by 78.9% and 70.0%, respectively, compared to that of the slab-free node RCSJ3. The ultimate bearing capacities improved by 13.2% and 9.98%, respectively, and the energy dissipation capacity increased by 23%. Additionally, the variation in the axial load ratio has multiple effects on the seismic performance of the joints. Increasing the slab thickness significantly enhances the seismic performance of the joints under positive loading. The bolt pre-tensioning force has a crucial impact on improving the bearing capacity and overall stiffness of the joints. The reinforcement ratio of the slabs has a notable effect on the seismic performance of the joints under negative loading, while the concrete strength of the slabs has a relatively minor impact on the seismic performance of the joints. Therefore, the reasonable design of these parameters can optimize the seismic performance of joints, providing a theoretical basis and recommendations for engineering application and optimization. Full article

The pre-inserted method for precast shear walls involves casting concealed beams at floor slabs between upper and lower structures, with precast concrete supports spaced at intervals. Vertical rebars at the base of upper walls are pre-inserted and anchored in the beams before slab casting. It offers advantages such as convenient construction without the need for grouting, demonstrating broad application prospects and significant promotional value. To evaluate seismic performance, quasi-static cyclic loading tests were conducted on five specimens: three full-scale pre-inserted precast walls and two cast-in-place counterparts. Under increasing lateral displacement, low axial-load specimens failed via tensile fracture of the outermost rebars, while high axial-load specimens failed by concrete crushing in compression. The test results showed that under identical axial-load ratios, the precast walls exhibited comparable bearing capacity, stiffness degradation, and energy dissipation to cast-in-place walls, but superior deformation ductility. The ultimate drift ratios of pre-inserted walls exceeded those of cast-in-place walls by 16.7% (axial-load ratio 0.2) and 22.2% (axial-load ratio 0.4), demonstrating robust seismic performance. Full article

The connection zones between precast concrete composite slabs and composite walls commonly experience severe reinforcement conflicts due to protruding rebars, significantly reducing construction efficiency. To address this, a novel slotted concrete composite slab–composite shear wall (SCS-CW) connection without protruding rebars is proposed in this study. In this novel connection, rectangular slots are introduced at the ends of the precast slabs, and lap-spliced reinforcement is placed within the slots to enable force transfer across the joint region. To investigate the static performance of SCS-CW connections, four groups of connection specimens were designed and fabricated. Using the structural detailing of the connection zone as the variable parameter, the mechanical performance of each specimen group was analyzed. The results show that the specimens demonstrated bending failure behavior. The key failure modes were yielding of the longitudinal reinforcement in the post-cast layer, yielding of the lap-spliced reinforcement, and concrete crushing at the precast slab ends within the plastic hinge zone. Compared to composite slab–composite wall connections with protruding rebars, the SCS-CW connections demonstrated superior ductility and a higher load-carrying capacity, satisfying the design requirements. Additionally, it was revealed that the anchorage length of lap-spliced reinforcement significantly affected the ultimate load-carrying capacity and ductility of SCS-CW connections, thus highlighting anchorage length as a critical design parameter for these connections. This study also presents methods for calculating the flexural bearing capacity and flexural stiffness of SCS-CW connections. Finally, finite element modeling was conducted on the connections to further investigate the influences of the lap-spliced reinforcement quantity, diameter, and anchorage length on the mechanical performance of the connections, and corresponding design recommendations are provided. Full article

To address the research gap in gas blast resistance of composite precast assembled utility tunnels, this study investigates structural damage evolution and the mechanisms influencing parameters through validated numerical simulations. A three-dimensional numerical model, incorporating the Karagozian & Case (K&C) concrete damage model and tie-break contact algorithm, was developed using LS-DYNA. The first validation against composite precast concrete slab explosion tests confirmed the model’s reliability, with displacement peak errors below 10%. The second validation focuses on the blast resistance test conducted on an underground utility tunnel, revealing an error margin of less than 10%. Results indicate that the utility tunnel exhibits a progressive failure mode of “joint cracking-interface damage-midspan cracking” under explosive loads, with stiffness degradation observed in joint regions at a loading pressure of 700 kPa. Increasing the normal strength of the interface to 5 MPa suppresses 90% of interface delamination, whereas completely neglecting interface strength results in a 9.0% increase in midspan displacement. Concrete strength shows minimal impact (<2.5%) on displacement under high loading conditions (≥0.9 MPa), and increasing the reinforcement ratio from 0.44% to 0.56% reduces displacement of the roof slab by 10.5%. These findings of address the research gap in the gas explosion response of composite precast assembled utility tunnels and could have significant implications for enhancing the disaster resistance of urban underground spaces. Full article

Following World War II, the swift economic growth in construction and the soaring demand in urban regions led to the excessive extraction of natural resources like fossil fuels, minerals, forests and land. To tackle significant global challenges, including the consumption of natural resources, air pollution and climate change, radical changes have been suggested over the past decades. As part of this strategic initiative, prioritizing sustainability in construction has emerged as a crucial focus in the design of all projects. In order to identify the most environmentally sustainable reinforced concrete (RC) slab system, this research investigates the carbon emissions associated with various slab systems, including solid, voided slabs and precast floor systems. The results demonstrate that beam and slab floor and solid slabs have the highest embodied carbon due to the significant use of concrete and related materials, whereas voided slabs and two-way joist floors exhibit lower carbon emissions. The results indicate that the two-way joist system is the most environmentally advantageous option. For precast floor systems, post-tensioned concrete and hollow-core slabs demonstrate the lowest embodied carbon levels. This research provides practical recommendations for architects and engineers aimed at enhancing sustainable design methodologies. It emphasizes the importance of incorporating low-carbon materials as well as pioneering flooring technologies in upcoming construction initiatives to support the achievement of global sustainability objectives. Full article

In this study, seven wet joint specimens of contact U-bars are designed in order to evaluate the flexural behavior of the wet joints in precast concrete slabs through four-point bending tests. This study investigates the effects of lap length, wet joint width, and water stop strips on the flexural behavior. The test results show that the ultimate bending capacity of the specimen with a lap length of 240 mm is 13.4% and 17.7% higher than that of the specimens with 160 mm and 80 mm. Water stop strips weaken the ductility of the specimen. The numerical model is established in ABAQUS finite element software and verified by the experimental results. Based on both test outcomes and finite element analysis, this study analyzes the deterioration effect of U-bars on the concrete within wet joints and proposes a calculation formula for flexural bending capacity that accounts for this deterioration. The proposed formula is shown to effectively predict the flexural capacity, since the theoretical predictions and the test results differ by less than 10%. Full article

A precast concrete segmental box-girder bridge (PCSBGB) is one of the most popular styles of Accelerated Bridge Construction (ABC). To address some common challenges (low durability, poor integrity, and construction inconvenience) in PCSBGBs, this paper proposes a precast ultra-high-performance concrete (UHPC) segmental box-girder bridge (PUSBGB). In comparison to conventional PCSBGBs that use three-dimensional prestress, the PUSBGB adopts only one-dimensional (longitudinal) prestress. In addition, the thickness of the bottom/top plate and web of the UHPC box-girder are relatively thin, and as a result, the self-weight is significantly reduced. Considering the fact that the thickness of box-girder is thinner than the NC structure, the shear lag effect and risk of girder cracking may correspondingly increase when a PUSBGB is adopted in a long-span bridge. Thus, it is of essential necessity to explore the flexural behavior of a PUSBGB. In this work, a specimen with a scale (1:4) associated with a field bridge (a 102 m long simply supported PUSBGB with externally unbonded tendons) is fabricated and experimentally investigated. The mechanical behaviors of the PUSBGB are discussed, including the failure mode, the crack distribution pattern, the longitudinal strain of the UHPC plate, and the variation of tendon strain. It is found that in the elastic stage, the top slab of the UHPC box girder exhibits a significant shear lag effect, and this phenomenon is even more obvious after cracking. With the development of the cracks, the effective flange width is decreased (with a minimum value of 0.76), and the second-order effect is kept the same before the dominant crack appears (the reduction factor is around 0.95). Moreover, four existing code equations, e.g., ACI 440, ACI 318, ASSHTO, BS 8100, used to predict the stress in the externally unbonded tendons are examined. Furthermore, a finite element analysis (FEA) of the field bridge is conducted, and the theoretical calculation demonstrates that the flexural resistances of the proposed PUSBGB can comply with the design requirements of Chinese code under the ultimate limit states (ULSs). Full article

This study aims to investigate the bending load-bearing capacity of precast hollow composite slabs composed of ultra-high-performance concrete (UHPC) and Normal Concrete (NC). Through finite element numerical analysis and verification, this study analyzes various key factors influencing the performance of the composite slab, including the wall thickness of the square steel tube, the diameter of transverse reinforcing bars, the thickness of the precast bottom slab, and the strength grade of the concrete. The results indicate that the use of UHPC significantly enhances the bending performance of the composite slab. As the wall thickness of the square steel tube and the strength of UHPC increase, both the yield load and ultimate load capacity of the composite slab show considerable improvement. By conducting an in-depth analysis, this study identifies different stages of the composite slab during the loading process, including the cracking stage, yielding stage, and ultimate stage, thereby providing important foundations for optimizing structural design. Furthermore, a set of bending load-bearing capacity calculation formulas applicable to UHPC-NC precast hollow composite slabs is proposed, offering practical tools and theoretical support for engineering design and analysis. The innovation of this study lies not only in providing a profound understanding of the application of composite materials in architectural design but also in offering feasible solutions to the energy efficiency and safety challenges faced by the construction industry in the future. This research demonstrates the tremendous potential of ultra-high-performance concrete and its combinations in modern architecture, contributing to the sustainable development of construction technology. Full article

Prestressed, precast composite panels are a type of building component that combines prestressing technology with composite materials; but, for most of them, it is difficult to balance structural stress performance and assembly efficiency. This paper proposes a series of novel bidirectional, prestressed, prefabricated, composite slabs, aiming to enhance their bidirectional force characteristics and assembly efficiency. By implanting a kind of specially designed concrete movable core rib with the same geometry as the cavity in the hollow-core slab at medium spacing, the transverse stressing performance of the structure is enhanced without affecting the unidirectional structural performance. Then, in the pre-set transverse apertures, several pieces of unidirectional, prestressed, precast hollow-core slabs that are implanted in the core mold are connected in series with high-strength strands and prestressed; finally, we obtain a bidirectional, prestressed, prefabricated composite slab. Two types of slabs (i.e., 3.3 m × 4.5 m and 4.5 m × 4.5 m) are selected and their mechanical behavior is investigated experimentally and by the finite element method, and the results are in good agreement. The proposed bidirectional, prestressed, precast composite slab not only has better overall bearing performance but also improves the structural stiffness and assembly rate, which can greatly improve the economic benefits and is of great significance for the popularization and application of assembled concrete structures. Full article

In the domain of bridge I-beam joint construction, conventional approaches such as cast-in-place concrete with suspended formwork and ordinary reinforced concrete precast slabs entail numerous limitations. The former features complex procedures, elevated costs, and significant safety risks, while the latter is hindered by the heavy weight of precast slabs, which causes difficulties in transportation and hoisting, inconvenient installation, and high costs. Reactive powder concrete ultra-thin precast slab (RPCUPS) is regarded as a potential solution due to its superior properties. Nevertheless, at present, there is an acute paucity of experience and research regarding the application of RPCUPS in bridge I-beam joints, particularly on a large scale. In a certain actual engineering project, a scheme was proposed to employ RPCUPS with a mere thickness of 20 mm in the bridge I-beam joints. In this scheme, the quantity of slabs is substantial, amounting to over 600,000. This constitutes the research gap and impetus of this study, with the aim of filling the existing knowledge void and providing technical support for engineering endeavors. This research carried out an extensive experimental test to systematically investigate the mechanical properties and safety of RPCUPS. Firstly, the material performance experiments were conducted to determine the manufacturing process of RPCUPS that meets the performance requirements. Subsequently, loading experiments on specimens under multiple working conditions were performed to disclose the cracking load and ultimate load of the two main types of RPCUPS and to analyze the influences of fiber type, mixing type, steel mesh, and slab thickness on the mechanical properties of RPCUPS (keeps the same volume rate of steel in a slab). Key findings encompass the outstanding mechanical properties and high safety factors of RPCUPS under diverse working conditions. Finally, in light of the actual construction environment, safety verification of temporary loading during actual construction was executed to furnish solid technical support for the practical engineering application of RPCUPS. The experimental results indicate that RPCUPS has been successfully applied on a large scale in actual engineering projects, not only without augmenting the cost but also significantly reducing the construction period by approximately five months, conspicuously enhancing the construction efficiency. These discoveries not only validate the feasibility of RPCUPS in bridge I-beam joint construction but also offer valuable references and guidance for similar future projects. Full article

Delays in the installation process of precast concrete (PC) components significantly impact the project execution. However, traditional scheduling and risk assessment methods fail to consider this process complexity and uncertainty adequately. With a systematic approach, this study analyzed complex delay mechanisms in the PC installation of three component types (columns, beams, and slabs) using 1881 observations across five work steps. Specifically, this study used k-means clustering to divide the observations into groups with certain characteristics. These groups were assessed quantitatively using the delay intensity metric. Based on the assessment, this study revealed six severe delay paths for different component types, which may combine to generate severe combinations of delay factors, considering factors such as the component size, wind conditions, worker availability, and installation location. This research contributed to PC construction management by presenting a systematic analysis of delay factors and by proposing specific severe delay paths during PC installation, offering project managers a basis for schedule optimization and risk management. Full article

Ultra-high-performance concrete (UHPC) exhibits significantly higher tensile strength compared to normal concrete (NC). In this paper, the application of UHPC to the precast base plate of composite slabs was proposed, leading to the development of a reinforced truss UHPC-NC composite slab. This approach effectively enhanced the crack resistance of the slab. A finite element model (FEM) for the reinforced truss UHPC-NC composite slab was developed based on the ABAQUS (2016) platform, using appropriate material constitutive relationships for UHPC, NC, and steel reinforcement. The validity of the model was verified through comparison with relevant test results. Subsequently, the effects of parameters such as the cross-sectional area of the upper and lower truss chords, the reinforcement ratio of the precast base plate, the strength grade of the UHPC base plate, and the thickness of the UHPC base plate on the flexural capacity of the UHPC-NC composite slab were investigated. Finally, the equations for calculating the flexural capacity of the UHPC-NC composite slab were proposed. It was found that increasing the cross-sectional area of the lower truss chord improved the flexural capacity and stiffness of such slabs to some extent, though ductility was slightly reduced. On the other hand, increasing the upper chord cross-sectional area had limited impact on the flexural performance. Increasing the reinforcement ratio of the longitudinal reinforcement in the precast base plate significantly enhanced the load-bearing capacity and stiffness but similarly reduced ductility. As the UHPC grade of the precast base plate increased, the cracking load, yield load, and ultimate load of the slab also increased. However, when the UHPC grade exceeded C120, the improvement in flexural capacity became less significant. With an increase in thickness of the precast UHPC base plate, cracking, yield, and ultimate loads also rose, but ductility decreased. When the thickness of UHPC exceeded 60 mm, the increase in flexural capacity became modest. The proposed equations for calculating the flexural capacity of the reinforced truss UHPC-NC composite slab in the normal section agreed well with simulation results, providing theoretical and numerical support for the design and analysis of UHPC-NC composite slabs. Full article