Precast Concrete Components Research Articles

Understanding the role of nano-C-S-H-polycarboxylate composites on compressive strength and frost resistance of Portland-sulfoaluminate cement blended concretes

The use of sulfoaluminate cement (SAC) to improve the early performance of Portland cement (PC)-based materials is well known. However, studies on the properties of PC-SAC blended concretes with nano-C-S-H-polycarboxylate composites (CSH) as accelerator are scarce. In this study, the properties and microstructures of PC-SAC composites containing CSH were investigated. The compressive strength and frost resistance of mortar and concrete were tested. The improvement mechanism of PC-SAC with CSH was evaluated using multiple micro-testing methods. The results showed that adding CSH remarkably improved the early compressive strength of PC-SAC blended concretes within the curing age of 3 d. Moreover, the incorporation of CSH significantly increased the frost resistance of concretes. Specifically, adding 0.6 wt% CSH caused a reduction in the relative dynamic elastic modulus of concretes by 12.68%, 24.85%, and 9.24% after 50, 100, and 150 freeze–thaw cycles, respectively. Furthermore, CSH seeding accelerated PC-SAC hydration to generate more products and optimized the pore structure with a smaller pore size to improve the properties of cement composites. Using CSH to modify PC-SAC concretes contributes to the rapid demolding of precast concrete components and improves the service life of assembled concrete buildings in cold regions.

Distribution Features of Deviation and Determination of a Tolerance Method for Prefabricated Concrete Components

According to the current standards for prefabricated buildings, the dimensional tolerances of components are usually determined by experience, lacking a theoretical basis. This work demonstrates the mathematical distribution of the dimensional deviations of precast concrete components by measuring their three-dimensional dimensions. Utilizing the Kolmogorov–Smirnov test, the cumulative distribution function of dimension deviations was evaluated. In response to the fact that the tolerance division principle of equal upper and lower tolerance thresholds for prefabricated components in existing standards does not match the distribution of actual measured deviations of the components, this paper proposed a method for determining the tolerance values of prefabricated components based on the process capability index. The association between the process capability index and the qualification rate was utilized to determine the process capability index at a specified guarantee rate, which, in turn, determines the tolerance threshold values for various components. The results indicate that the range of unqualified random variables for the dimensional geometric parameters of the prefabricated components did not show a significant difference, with all values between 0.99 and 1.02. The coefficients of geometric parameter variation were all less than 0.0061, and the component dimensional deviation adhered to the normal distribution. By linking the process capability index with the pass rate, a process capability index of 0.55 at a guarantee rate of 90% was determined, along with the tolerance for various components.

Point cloud-based dimensional quality assessment of precast concrete components using deep learning

The dimensional quality of precast concrete (PC) subcomponents (concrete and rebars) should be inspected in advance to ensure assembly quality. Currently, PC components are mainly inspected in a manual manner using tools such as tape measure, which is error-prone and inefficient. This study developed an innovative approach for automatic dimensional quality assessment of PC components using point cloud-based deep learning techniques. The approach consists of 1) a dataset-generating method to automatically create the synthetic dataset of PC components’ point clouds, 2) an enhanced focal loss-based precast concrete component recognition net (PCCR-Net) employing hierarchical feature learning to segment the synthetic point clouds dataset into rebars and concrete (i.e. the synthetic dataset generated is used to train the PCCR-Net), and 3) a quantitative measurement protocol that can estimate the dimensional quality of the segmented concrete and rebars. Experiments were conducted to test the capability of the approach, and the results show that the proposed approach was able to yield satisfactory performance. First, the dataset-generating method can solve the shortage of point cloud datasets in engineering practice. Second, the PCCR-Net segmentation network can simultaneously realize the high-precision identification of various typical PC components, including PC columns, beams, slabs, and walls. Third, the dimension average deviations between experimental results and manual measurements demonstrate that the assessment approach can accurately estimate the dimensions of PC components.

DFMA-oriented modular and parametric design and secondary splitting of vertical PC components

The design and production of assembled buildings are difficult to standardise, which limits their extensive application. In this paper, the design for manufacture and assembly (DFMA) concept is applied to the design of vertical precast concrete (PC) components for assembled buildings. Taking vertical PC components as an example, the rapid modelling and whole life-cycle application of DFMA-oriented PC components for assembled buildings are investigated. Firstly, the modular design method is introduced. By combining parametric design and building information modelling (BIM), we propose a modular, parametric design method and process of PC components based on DFMA. Secondly, the design of standard modules after secondary splitting is introduced for a better DFMA-oriented parametric design of PC components. We explored the secondary development process of DFMA and BIM and the module creation process of the parametric standard based on family templates and DFMA. Thirdly, based on the parametric standard module, the application of the optimised whole life cycle of design, manufacture and assembly of PC components is introduced. Finally, the feasibility of this method is verified by practical cases. The design process for PC components is fast, accurate and standardised. The integrated application of BIM is accelerated, and digital collaboration in assembly construction is strengthened. The study results are conducive to establishing a standardised design and production system for PC components, reducing design costs, improving design efficiency and the comprehensive benefits of assembled buildings.

Development of Fragility Models for Precast Concrete Shear Walls and Columns Connected by Grouted Sleeves

Performance-based seismic design and assessment of precast concrete (PC) structures have been widely studied. Fragility models for PC components have rarely been developed; however, it is a critical foundation for the above-mentioned design and assessment. Hence, this study was focused on developing fragility models for PC shear walls (PCSWs) and columns (PCCs) connected using grouted sleeves. To this end, 46 full-scale PCSWs and 45 full-scale PCCs, connected using grouted sleeves, were collected, and their test results were analyzed. Six damage states (DSs) were recommended based on the typical damage characteristics and with reference to the associated reinforced concrete (RC) components. Subsequently, the fragility models of PCSW and PCC were established for each DS using the drift ratio as the engineering demand parameter. In addition, the influence of the design axial load ratio on the fragility models was revealed. Through the comparison of fragility models between the PC and RC components, differences in parameters and curves of fragility models were quantitatively compared. These study achievements can serve as valuable references for performance-based seismic design and assessment of PC structures connected using grouted sleeves.

Applicability of Using Precast Concrete Components of Gate Posts for the Construction of the Floodgate Which Will Prevent Japan’s Largest Tsunami

Applicability of Using Precast Concrete Components of Gate Posts for the Construction of the Floodgate Which Will Prevent Japan’s Largest Tsunami

The new ACI code for the design of GFRP reinforced concrete

The American Concrete Institute has published ACI 440.11-22, Building Code Requirements for Structural Concrete Reinforced with Glass Fiber-Reinforced Polymer (GFRP) Bars—Code and Commentary. This new code was developed by an American National Standards Institute–approved consensus process and addresses structural systems, members, and connections, including cast-in-place, precast, nonprestressed, and composite concrete construction. ACI 440.11-22 is the first comprehensive building code covering the use of nonmetallic, GFRP reinforcing bars in structural concrete applications. This article provides background on this new code and discusses potential uses for precast concrete components and structures.

Performance of precast concrete bridge piers with grouted sleeve connections against vehicle impact

The bridge failure caused by vehicle impact is a great potential traffic danger. According to the new trend of bridge industrialization construction, this study aims to explore the dynamic behavior and failure modes of precast concrete (PC) piers with grouted sleeve connections against vehicle impact. Finite element (FE) models of PC components under impact loadings are developed and calibrated against experimental tests. Then, the calibrated simulation method of grouted sleeve connection is utilized to establish the numerical model of PC piers subjected to vehicle impact, and a comparative analysis is conducted to distinguish the impact responses of PC piers and reinforced concrete (RC) piers. A curvature-based method is proposed for the damage evaluation of the impacted PC piers. Further, intensive numerical simulations are performed to identify the effectiveness of sleeve location, interface shear strength, tensile strength of grouted sleeve, and axial force on the dynamic behavior of PC piers. The results show that the impact forces of RC and PC piers are almost identical, but the resistance mechanism of PC piers at the base varies from the shear-flexural mechanism to the truss-arch mechanism in the impact process. The proposed curvature-based method could intuitively describe damage details of PC piers, especially local damage. The grouted sleeve enhances the stiffness and capacity of the pier column in the sleeve region, and sleeve defects shall be avoided in the construction stage. The grouted layer would weaken the pier integrity, and thus obvious cracking and sliding are likely to appear at the interface. To some extent, increasing the axial force could improve the impact capacity of PC piers.

Using recycled aggregate concrete at a precast-concrete plant: A multi-criteria company-oriented feasibility study

Numerous test results at laboratory scale confirm the utility of Recycled Aggregate (RA) for the development of concrete that demonstrates durability and adequate in-fresh and mechanical behavior. However, feasibility evaluations of the use of RA in real industrial applications are necessary, before any large-scale industrial application of these products can begin. In this research, the feasibility of producing precast-concrete components containing large amounts of coarse RA at a precast-concrete plant is analyzed. Two Self-Compacting Concretes (SCC) were produced incorporating 0% and 100% coarse RA, respectively, at both laboratory scale (0.08 m3) and industrial scale (2 m3). Work took place at the industrial-scale facilities of a precast-concrete company that was collaborating in this study. Flowability and mechanical behavior were maintained as concrete production volumes increased, and concrete strength even increased after adding coarse RA, due to a careful mix design. However, the durability performance worsened by around 20% when produced at industrial scale, being this worsening higher whether coarse RA was used. A Multi-Criteria Decision-Making (MCDM) analysis, in which the criteria of the precast-concrete company defined the relative importance of each concrete property, showed the feasibility of manufacturing precast-SCC components containing coarse RA for interior usage, whose fundamental requirement is adequate mechanical strength. The results of the MCDM analysis also underlined the lower cost of coarse RA, making its use in SCC components cast with large concrete volumes advisable. Overall, the addition of coarse RA in the precast-concrete industry is recommended in the interests of a greener construction sector.

Study on anti-collision behavior of new precast concrete curb components in a highway tunnel

In order to improve the prefabrication level of highway mountain tunnels, improve the quality of the project, and shorten the construction period, a new type of prefabricated concrete curb member was developed based on an actual project. The production process, construction technical points, and on-site assembly technology are discussed. In addition, a method to calculate the anti-collision performance of the curb components is proposed, that is, the collision force of 850 kN was calculated by the pseudo-static method, and then finite element simulation analysis was used to obtain the stress of the concrete structure and reinforcement. The results show that the reinforcement will not fail, which will ensure the curb component will not undergo brittle fracture. This study provides a reference to improve the prefabrication level of highway tunnels.

Flexural behavior of precast concrete beams in-span assembled with bolt-steel plate joints

The assembly of precast concrete structural components is primarily concentrated at the splicing joints of the components. Wet connections involving additional stirrups and detailing cause casting difficulties and possibly deficient joints. Herein, a new type of precast beam in-span assembled with bolt–steel plate joints (PBSPB) is proposed. A significant unique feature is the discontinuous longitudinal reinforcement in the midspan, where the U-shaped steel plate covers the web and tensile zone of the concrete beam. The steel plates and bolts are used to connect the two assembled short beams to resist both flexure and shear owing to the external effects. To investigate the effects of the steel-plate thickness and span–depth ratio on the flexural behavior of beams, a static behavior test was conducted on six PBSPBs and one cast-in-situ beam. The failure mechanisms of the PBSPBs and cast-in-situ beam were examined and compared with regard to the crack propagation, load–displacement characteristics, and strain responses. All the PBSPBs exhibited excellent performance with limited cracks under identical conditions; only minor damage was observed, which consisted of small amounts of concrete spalling and edge warping of the steel plates. Finite-element analysis (ABAQUS) models of the proposed PBSPBs were developed to verify the ultimate load and damage situations of each specimen, a simplified flexural-capacity calculation formula for the PBSPB was developed, and the theoretical results were consistent with the experimental results. The results indicated that the new precast concrete beams had favorable flexural capacities. The beam with thicker steel plates in the span had a higher strength owing to the higher stiffness. Increasing the span–depth ratio increased the ultimate load and barely affected the failure mechanism.

Experimental Study of Emulative Precast Concrete Beam-to-Column Connections Locally Reinforced by U-Shaped UHPC Shells.

Precast beam–column connections act as vital elements of precast concrete frames. To enhance the resistance to the earthquake-induced damage and environment-induced deterioration of precast beam–column connections, an innovative precast concrete beam-to-column connection locally enhanced by prefabricated ultra-high-performance concrete (UHPC) shells was proposed. For studying the seismic behaviors of these novel connections and the influence caused by the prefabricated UHPC shell length, full-scale precast specimens were experimentally investigated using low-cyclic reversed loading tests. The obtained results were analyzed and discussed, including hysteresis curves, skeleton curves, strength and deformability, performance degradation, energy dissipation capacities, and plastic hinge length. The results reveal that the novel precast concrete beam–column connections with UHPC shells behaved satisfactorily under seismic loadings. The damage in the concrete near the lower part of the beam end is reduced by the prefabricated UHPC shells. The longer prefabricated UHPC shells were more useful for decreasing the damage to the precast concrete components and improved the structural performance. The precast specimen with 600-mm long UHPC shells can achieve a ductility of 4.87 and 4.0% higher strength than the monolithic reference specimen.

Vision-based trajectory monitoring for assembly alignment of precast concrete bridge components

The prefabricated structures are popularly used because of their high efficiency and it is important to ensure their installation quality. The current installation is guided by visual observation and total station, which is inaccurate and time-consuming. This study presents a stereo-vision-based pose measurement technique for guiding the installation to address the problems. The contributions are as follows: 1) A framework of a vision-based 6-DOF pose monitoring system is designed to track the precast member continuously; 2) A two-level adjustment strategy is suggested by transferring the relative pose measurement between the precast member and existing structure to the process to determine the relative relations of two coordinate systems; 3) A robust deep-learning-based ellipse detection method is proposed to identify and classify the artificial targets accurately. The proposed technique is evaluated in both indoor experiments and the construction of an expressway viaduct to demonstrate its accuracy and effectiveness.

Insight into the local C-S-H structure and its evolution mechanism controlled by curing regime and Ca/Si ratio

Calcium silicate hydrate (C-S-H), as the main hydration product in hardened Portland cement, significantly affects its mechanical properties and durability. A profound insight into nanostructured C-S-H is of great significance for tailoring the microstructure and performance of cementitious materials. However, the effect of high temperature and pressure, which is widely adopted in manufacturing precast concrete components, on the microstructural evolution of C-S-H lacks a systematic study. In this study, the structural features of C-S-H with Ca/Si ratios of 0.83, 1.0, and 1.5, synthesised by calcium oxide and fumed silica curing under steam (80 °C) and autoclaving (180 °C, 1 MPa) conditions were investigated, where a room temperature (25 °C) curing was used as a reference. The chemical components, along with structural and morphological features of C-S-H, were characterised at a multi-scale level using X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, nuclear magnetic resonance spectroscopy, scanning electron microscopy, transmission electron microscopy, and N2 adsorption. The results prove that autoclave curing can improve the crystallinity of C-S-H and destroy the gel pores more than steam curing. A flaky tobermorite and fibrous xonotlite at Ca/Si ratios of 0.83 and 1.0, respectively, are characterised as the main structure. Autoclave curing significantly contributes to an increasing degree of polymerisation of C-S-H owing to the interlayer dehydration and crystalline transformation, with Q2 units directly converted to Q3. When the Ca/Si ratio is increased to 1.5, the decalcification of C-S-H caused by carbonisation contributed to a high polymerisation in the C-S-H structure. The rising temperature promotes the formation of C-S-H with a high Ca/Si ratio, thus exhibiting Q1 units. A detailed exploration of the C-S-H structure helps optimise the mixture and fabrication process according to the performance requirements of precast concrete components.

Exploring Key Factors for Contractors in Opening Prefabrication Factories: A Chinese Case Study.

Adoption of prefabrication is essential for improving the urban built environment. However, the existing prefabrication market in China is far from mature. As the stakeholder who conducts construction activities, the contractor is facing a dilemma of lacking steady prefabricated components supply. In this circumstance, a potential solution is that contractors open their own prefabrication factories to guarantee stable component supply. The aim of this research is exploring the key factors for contractors to open prefabrication factories. Firstly, a total of 28 influencing factors were identified from literature. Then, the identified factors were divided into four categories: policy environment, market environment, technological environment, and enterprise internal environment. Through interviews with experienced professionals, a total of 19 factors were selected for future analysis. Based on the 19 factors, a questionnaire was designed and distributed to the experts to rate the degree of mutual influences. The collected data were analyzed using Ucinet6.0 software, and the adjacency matrix and the visual models were established. Finally, through the analysis of node centrality, betweenness centrality, and closeness centrality, the four key influencing factors were determined including mandatory implementation policy, precast concrete component's price, market demand, and contractor's strategic objectives. The results of this study could assist contractors in making decisions of opening their own prefabrication factories toward more sustainable environment.

Shear performance of the interfaces for precast concrete shear wall components by novel preparation method

AbstractFor emulating cast‐in‐place (CIP) precast concrete (PC) shear wall structures in China, the adjacent PC shear wall components are joined by vertical post‐cast concrete. Shear behavior of concrete‐to‐concrete interfaces is critical for structural integrity. A novel preparation method, as cast using bubble film (BF) form, is proposed. Shear performance experiments are conducted to obtain the shear capacity and deformation characteristic of the specimens by the preparation methods of hydro‐demolition (HD), as‐cast by patterned steel plate (PSP) form and BF. Concrete strength and shear reinforcement are also considered. By comparison with reference CIP specimens, HD specimens performs best, followed by BF specimens, and the worst are PSP specimens. The collected shear loads for HD and BF specimens are larger than calculated results under diagonal shear failure, assuring structural integrity. Concrete strength and shear reinforcements have effective influence on interface shear capacity. Shear reinforcements with small diameter and small spacing are recommended.

Study on Complexity of Precast Concrete Components and Its Influence on Production Efficiency

Prefabricated construction has been well recognized for its benefits, including accelerated construction cycle time and improved sustainability. However, low efficiency in the production of precast concrete components due to component and production complexity has not been sufficiently addressed in previous research. This paper explores the complexity of precast concrete components by establishing complexity indices and evaluating their influence on production efficiency. First, referring to research on product complexity in the machinery manufacturing industry, we define the complexity of precast concrete components in the construction industry. Then, based on a literature review, field studies, and expert interviews, we systematically construct the complexity indices of precast concrete components using the three‐stage coding method, Grounded Theory. The overall complexity index system for precast concrete components constructed comprises 16 constituent complexity indices in three dimensions (i.e., structural complexity of the component, production complexity, and management complexity). The relationship between complexity indices and production efficiency is then explored using structural equation model analysis based on the data collected through a questionnaire survey. The results reveal that complexity indices have a significant impact on the production efficiency for precast concrete components, where the number of embedded parts, waiting time in production, operating proficiency of workers, and degree of automation of the production line are found to be the most influential complexity indices. This study provides a foundation upon which production managers improve production efficiency for precast concrete components based on an analysis of their product complexity.

Site Selection of Precast Concrete Component Factory Based on PCA and GIS

In China, with the expansion of the prefabricated construction market, the demand for precast concrete (PC) components is increasing and the construction of production plants to meet this need is expanding. To address the problem of siting PC component plants in China's construction industry, a combination of qualitative and quantitative analysis using principal component analysis (PCA) and geographic information system (GIS) is proposed for their siting. Taking the site selection process of a PC component plant in Wuhan, Hubei Province, China as an example, the diamond model is combined with six dimensions of environmental factors, requirements, regional competition, related and supporting industries, technological innovation and policies and regulations to construct an indicator system for PC component plant site selection. In the preliminary selection stage, PCA was applied to analyze the site selection indexes to obtain the overall score and ranking of each district for the selection of PC component plants in Wuhan, and it was concluded that three districts, namely, Xinzhou, Hannan, and Huangpi, were more suitable for the construction of component plants. In the precise selection stage, based on the availability of data, Hannan was selected among the three areas suitable for site selection for GIS analysis, using the visual‐spatial analysis function of GIS to quantify the four geographical information indicators of environmental factors, and the results showed that Area C in Hannan was the most suitable area. The results show that the method has high accuracy and good applicability.

Hydrological Effects of Prefabricated Permeable Pavements on Parking Lots

Permeable pavements can infiltrate and reduce stormwater runoff in parking lots, but issues around long construction periods and proper maintenance still required proper research and further understanding. The application of precast concrete can help to solve this. In this study, precast concrete components were applied to the design of permeable pavements to form prefabricated permeable pavements. The laboratory study is one of the first to examine the hydrological effect of prefabricated pervious pavements in parking lots. Four kinds of permeable pavements were designed and manufactured. These had different materials (natural sand-gravel, medium sand) which comprised the leveling layer or different assembly forms of precast concrete at the base. Three scenarios of rainfall intensity (0.5, 1, and 2 mm/min) and three rainfall intervals (one, three, and seven days) were simulated using rainfall simulators. The initial runoff time, runoff coefficient, and runoff control rate of each permeable pavement were investigated during the process of simulating. Results showed that the initial runoff time was no earlier than 42 min, the maximum runoff coefficient was 0.52, and the minimum runoff control rate was 47.7% within the rainfall intensity of 2 mm/min. The initial runoff time of each permeable pavement was no earlier than 36 min when the rainfall interval was one day, whereas, the maximum runoff coefficient was 0.64, and the average runoff control rate was 41.5%. The leveling layer material had a greater impact on the hydrological effect of permeable pavements, while the assembly form of precast concrete had no significant effect. Compared with natural sand-gravel, when the leveling layer was medium sand, the runoff generation was advanced by 4.5–7.8 min under different rainfall intensities, and 7–10 min under different rainfall intervals. The maximum runoff coefficient increased with about 14.6% when the rainfall interval was one day. Among four kinds of permeable pavements, the type I permeable pavement had the best runoff regulation performance. The results revealed that all prefabricated permeable pavements used in this study had good runoff control performance, and this design idea proved to be an alternative for the future design of permeable pavements.

Acceptance model of precast concrete components in building construction based on Technology Acceptance Model (TAM) and Technology, Organization, and Environment (TOE) framework

According to the increasing development of prefabrication as a sustainable alternative approach to conventional construction methods, the use of Precast Concrete Components (PCC) has received more attention. This method provides advantages such as improved construction speed, labor productivity, and lower waste of resources. It has also been suggested as an immediate response to the social need of housing demand. However, in some countries, most concrete buildings are still built using traditional methods. Considering the importance of promoting the use of PCC in building construction, this study aims to develop a model based on the Technology Acceptance Model (TAM) and the Technology, Organization, and Environment (TOE) framework to quantitatively investigate the influencing factors on adopting PCC from both individual and organizational perspectives. The proposed model was analyzed with the Partial Least Squares Structural Equation Modeling (PLS-SEM) method. The results showed improving engineers' understanding of PCC's advantages, strengthening the competitive atmosphere between organizations besides government support for builders to use PCC, had the greatest role in adopting this approach. In addition, the indirect effects of perceived risks and costs on PCC adoption through engineers' understanding of the benefits of this method were significant. The moderation effect of civil engineers' experience was also investigated on the relationship between influencing factors and intention to adopt PCC. The findings of this study may help economic and educational policymakers to develop prefabrication using PCC. New insights have also been presented by the current study to conduct more quantitative and qualitative research in the prefabrication context.