Precast Production Research Articles

Scheduling redundancy optimization for precast production to enhance disruption management in prefabricated construction

Redundancy is a highly effective approach for minimizing losses in precast production when faced with inevitable disruptions. However, existing studies have primarily focused on enhancing production redundancy in order to mitigate losses caused by disruptions, without considering the added production costs resulting from decreased efficiency. Besides, the cost-effectiveness of redundancy design may be influenced by the disruption types and their associated risk levels, which has not been thoroughly investigated. In this paper, a redundancy optimization model for precast production is proposed to achieve the trade-off between the redundancy benefits and the additional costs involved. The concept of production scheduling redundancy is firstly defined, and the benefits derived from its implementation are quantified. Additionally, different scenarios with high, moderate, and low occurrence levels of disruptions are designed to optimize the production redundancy in different situations. On this basis, the effectiveness and cost-benefits of redundancy are compared subject to various types and levels of disruptions. Finally, a case study is conducted to illustrate the model. The findings show that the machine breakdown is the most critical disruption in the precast production, and implementing redundancy measures prove to be more cost-effective in situations characterized by higher levels of risk. Besides, the optimal degree of redundancy is related to both the levels and the types of disruptions. The methodology of this paper can provide insights for disruption management in precast production and give full play to the benefits of prefabricated construction.

An optimization model for just-in-time (JIT) delivery of precast components considering 3D loading constraints, real-time road conditions and assembly time

PurposeAlthough extensive research has been conducted on precast production, irregular component loading constraints have received little attention, resulting in limitations for transportation cost optimization. Traditional irregular component loading methods are based on past performance, which frequently wastes vehicle space. Additionally, real-time road conditions, precast component assembly times, and delivery vehicle waiting times due to equipment constraints at the construction site affect transportation time and overall transportation costs. Therefore, this paper aims to provide an optimization model for Just-In-Time (JIT) delivery of precast components considering 3D loading constraints, real-time road conditions and assembly time.Design/methodology/approachIn order to propose a JIT (just-in-time) delivery optimization model, the effects of the sizes of irregular precast components, the assembly time, and the loading methods are considered in the 3D loading constraint model. In addition, for JIT delivery, incorporating real-time road conditions in the transportation process is essential to mitigate delays in the delivery of precast components. The 3D precast component loading problem is solved by using a hybrid genetic algorithm which mixes the genetic algorithm and the simulated annealing algorithm.FindingsA real case study was used to validate the JIT delivery optimization model. The results indicated this study contributes to the optimization of strategies for loading irregular precast components and the reduction of transportation costs by 5.38%.Originality/valueThis study establishes a JIT delivery optimization model with the aim of reducing transportation costs by considering 3D loading constraints, real-time road conditions and assembly time. The irregular precast component is simplified into 3D bounding box and loaded with three-space division heuristic packing algorithm. In addition, the hybrid algorithm mixing the genetic algorithm and the simulated annealing algorithm is to solve the 3D container loading problem, which provides both global search capability and the ability to perform local searching. The JIT delivery optimization model can provide decision-makers with a more comprehensive and economical strategy for loading and transporting irregular precast components.

Group technology empowering optimization of mixed-flow precast production in off-site construction.

Faced with immense pressure to reduce environmental impact, off-site construction (OSC) is considered a sustainable alternative to conventional practices. However, challenged by component diversity and a significant surge in demand, deficient or empirical-based scheduling management struggles to effectively harness the potential of mixed-flow precast production to improve efficiency, instead resulting in environmental impacts, and falling short of expected benefits in OSC projects. Therefore, this study addresses the conflict between efficiency and environmental impact arising from the application of mixed-flow precast production by integrating multi-objective optimization and group technology. A multi-objective optimization framework is proposed, incorporating grouping technology for mixed-flow precast production scheduling and aiming to minimize carbon emissions and reduce tardiness/earliness penalty. The non-dominated sorting genetic algorithm II (NSGA-II), adjusted by adaptive population initialization strategy and group technology, is introduced to solve this problem, striking a balance between sustainability and penalty costs. Through a real-case analysis, the proposed approach demonstrates an average reduction of 37.5% in carbon emissions compared to rule-based scheduling methods, a 30.1% reduction compared to previous research methods, along with over 10% reduction in tardiness/earliness penalty. This study enhances environmental benefits and efficiency from a production scheduling perspective and establishes an automated, practical method, fostering low-cost, high-efficiency green production for construction component enterprises, particularly for small and medium-sized enterprises, thereby promoting sustainable development in the construction industry.

Flowshop scheduling optimization for multi-shift precast production with on-time delivery

With the increasing popularity of prefabricated construction around the world, precast plants face increasingly complex production scenarios. Because it is important for precast components to be delivered on time and assembled according to the planned schedule, it is a common phenomenon to increase production shifts and break the routine production schedule to meet time-pressured orders. But there is still a lack of research on flowshop multi-shift scheduling methods in precast production. To address this issue, a flowshop scheduling optimization model of multi-shift precast production with on-time delivery is established, which is the application in civil engineering. A solution framework and its corresponding optimization processes are designed to avoid a combinatorial explosion of solutions and save solution time, which is contribution in artificial intelligence. The validity of the model is proven using a practical case. The results show that, compared to the conventional scheduling method, the proposed method significantly reduces costs under on-time delivery and stably obtains optimized feasible scheduling schemes.

Production scheduling of prefabricated components considering delivery methods

To address the processing scheduling problem involving multiple molds, components, and floors, we propose the Genetic Grey Wolf Optimizer (GGA) as a means to optimize the production scheduling of components in a production line. This approach combines the Grey Wolf algorithm with the genetic algorithm. Previous methods have overlooked the storage requirements arising from the delivery characteristics of prefabricated components, often resulting in unnecessary storage costs. Intelligent algorithms have been demonstrated to be effective in production scheduling, and thus, to enhance the efficiency of prefabricated component production scheduling, our study presents a model incorporating a production objective function. This model takes into account production resources and delivery characteristics constraints. Subsequently, we develop a hybrid algorithm, combining the grey wolf algorithm with the genetic algorithm, to search for the optimal solution with a minimal storage cost. We validate the model using a case study, and the experimental results demonstrate that GAGWO successfully identifies the best precast production schedule. Furthermore, the precast production plan, considering the delivery method, is found to be reasonable.

Just-in-Time Precast Production Scheduling Using Dominance Rule-Based Genetic Algorithm.

The objective of this study is to provide a model and method to assist fabricators in making appropriate precast production plans, coordinating factories prefabrication and on-site assembly in construction based on the just-in-time (JIT) philosophy. We propose a JIT precast production scheduling model for the precast production of steel box girders in the Hong Kong-Zhuhai-Macau (HZM) bridge construction project. In order to minimize the total early/tardy costs for this JIT scheduling model, we first present a job batching algorithm (JBA) to group series of jobs into several batches. Then, we model the batch cost function as a piecewise linear convex function and derive its optimal solution, which guides us to propose an optimal shifting algorithm (OSA) to locate the optimal starting time of each batch and minimize the batch cost. In order to get the best job sequence for minimizing the total early/tardy costs and improve search efficiency, we introduce a dominance rule for early/tardy scheduling problem and propose a dominance rule-based genetic algorithm (DBGA) embedded with an optimal timing algorithm, which can find the best job sequence as well as the corresponding optimal schedule. The real-world case study of HZM bridge project demonstrates that our proposed model and algorithm can assist construction practitioners to make better decision on precast production scheduling compared to empirical rule in current engineering practice. In addition, numerical studies prove that our proposed algorithm has a better performance on both effectiveness and efficiency due to the dominance rule.

Green optimization for precast production rescheduling based on disruption management

The advancement of prefabricated buildings has become a prominent trend in the construction sector. Disturbance events as a significant obstacle to the production of prefabricated components, restricting the realization of green, efficient, and sustainable advantages in prefabricated construction. This study examines how different disturbance events can affect precast production rescheduling and the selection of rescheduling schemes based on different carbon emissions scenarios. To attain dynamic disruption management while simultaneously considering carbon emissions in production, a three-layer scheduling disruption management model which includes two production lines is established, which seeks to minimize the maximum completion time, the earliness and tardiness penalty, and carbon emissions. Then an improved non-dominated sorting genetic optimization algorithm is devised to tackle the proposed model. Furthermore, two scenarios, specifically increased PC production types and advanced PC due dates, are explored to accurately depict real-life production environments. A case study is subsequently utilized to validate the efficacy of the proposed model. The disruption management rescheduling model result in cost savings of 16.5% and 50%, as well as carbon emissions reductions of 1.5% and 9.1%, respectively. The empirical findings from the case study reveal that both the developed model and the refined algorithm are practical and efficient. This research contributes to the development of rescheduling schemes for prefab manufacturers, addressing both customer satisfaction and demands for green production, ultimately improving overall project performance.

An Implementation of Lean Approach to Achieve Working Time Efficiency in Precast Factory

Question: Can the 5S lean approach using Seiri (Sorting), Seiton (Arranging), Seiso (Cleaning), Seiketsu (Standardizing), and Shitsuke (Sustaining) improve the workflow to achieve efficiency in the working time needed to produce Corrugated Concrete Sheet Pile (CCSP)? Purpose: The aim of this study is to offer modification of work processes by implementing a lean approach using 5S to eliminate waste and improve working time. Research Method: Data were collected by practitioner interview and in-depth observation to obtain a completed understanding work process of the precast production cycle. Then, Bizagi Modeler 2.0 was used to determine the mapping of the production cycle and the total time duration. Process Activity Mapping is used to determine the problems contained in the cycle, especially activities that are NVA. Then, a modification of work processes used a lean approach with 5S concept to eliminate non-value added (NVA) activities and achieve working time efficiency. Findings: Based on the research results, it was found that there were two problems in the CCSP concrete production cycle. The first was the strand cutting activity, delayed since it was performed with a lack of workers. The second was the delivery ready mix was categorized as a delay activity that needs to be eliminated. Both of these problems were addressed with 5S. Seiri is applied by doing a standard operating procedure completed with the number of workers for each work item. At the same time, Seiton concepts are conducted by moving the batching plant. The improvement has resulted in: a decreased execution time of strand cutting from 129.23 minutes down to 64.8 minutes (50%), an elimination of delivery ready-mix as a delay activity (NVA activity) which can save 15.13 minutes of production time, and a shortened working time of concrete bucket loading from 10 minutes to 5 minutes (50%). All the working time savings are obtained in the production cycle. Before the improvement it took 33 days to complete 25 production cycle of CCSP. After the improvements the 25 CCSP production cycle took 31.5 days (4.5% efficiency). Limitations: This study mainly focused on a 5S lean approach with Bizagi Modeler software and Process Activity Mapping method at a precast factory producing CCSP. Implications: This research will provide guidance for applying the 5S lean approach relative to time efficiency in a construction company and can also inspire further research to develop alternative lean approaches. Value for Practitioners: This paper presents the impact of applying the 5S lean approach to minimize wastage in the production cycle in order to achieve time efficiency, with an emphasis on construction supply factories wishing to adopt lean. Keywords: 5S, Bizagi Modeler, Lean Approach, Process Activity mapping, Time Efficiency Paper type: Case Study

IMPROVED EIGHT-PROCESS MODEL OF PRECAST COMPONENT PRODUCTION SCHEDULING CONSIDERING RESOURCE CONSTRAINTS

Reasonable production scheduling plays a vital role in the production of precast component factories. However, previous static scheduling models no longer fit actual production. In particular, some factors will cause errors in the actual delivery time of the components, including the lack or redundancy of processes in the model, resource constraints required by the core processes, and differences in transportation schemes. Moreover, the optimization goal of simply pursuing the minimization of fines from order delivery underestimates companies’ emphases on reputation. Therefore, this study proposes an improved model for precast component production scheduling considering resource constraints. The number of production processes is adjusted to eight, and three resource constraints for mold, steel, and concrete are added. An enterprise decision-making coefficient is introduced into the optimization object function, and the constraints of the transportation scheme are improved. Finally, a real case study is conducted to verify the applicability of the model. Compared with previous models, the developed model fills the gap in considering production resource constraints and enterprise decisions in precast production, can better meet diverse production conditions and business needs of factories for scheduling, and help give full play to the advantages of prefabricated construction.

Value losses and environmental impacts in the construction industry – Tradeoffs or correlates?

Construction activities have significant adverse impacts on the environment which typically include dust and gas emissions, noise pollution, waste generation, water consumption, and air pollution. One step towards a more sustainable construction industry during the production stage is producing precast construction components in manufacturing facilities. However, most precast facilities are not yet able to track value losses such as waste from time and scrap. The main objective of this article is to examine the correlation between those value losses and the environmental impact with Cost Efficiency Accounting - a new measurement method applied to the best of our knowledge for the first time in the construction industry. We collected data on 460 products within a precast production facility and analyzed how the material used (steel, concrete, etc.) correlates with the production times and the complexity of the products. On the basis of these results, we found that high costs are related to negative environmental impacts, but we also discuss implications of the results for improving the environmental and economic performance of the construction industry simultaneously.

Optimized ultra-high-performance concrete horizontally curved bridge superstructure

Horizontally curved bridges have been mostly built with steel plate I-girders or tub girders. In the past 15 years, curved concrete girders have been successfully used in several states, including Nebraska, Colorado, and Flor­ida. This paper addresses the design of curved concrete girder bridges using ultra-high-performance concrete (UHPC) by combining state-of-the-art spliced girder technology and UHPC technology. It also proposes a number of unique features that result in further simplifi­cation of precast concrete production and construction. Critical design criteria are discussed. The system devel­opment of curved UHPC girder bridges and necessary construction steps are elaborated through a numerical example of a three-span bridge, which shows greatly reduced concrete quantities when compared with re­cently constructed curved concrete girders. With UHPC designed as proposed here, horizontally curved bridges are expected to be cost competitive with conventional concrete and more economical than structural steel.

Sustainability Evaluation Using a Life Cycle and Circular Economy Approach in Precast Concrete with Waste Incorporation

Waste valorisation as secondary or alternative raw materials in several sectors products and processes has been an important way to implement a more sustainable and circular way to manage the efficient use of natural resources. This action contributes not only to save natural resources but also to prevent sending large amounts of wastes, some of them dangerous, to landfill disposal, creating a major environmental, economic and social impact. To promote circular economy, this work attempts to demonstrate the environmental gains in a competitive way, by bringing together in an industrial symbiosis action, two large producing sectors (the pulp and paper industry and concrete construction sector), which are also able to consume significant amounts of resources and to generate large amounts of wastes. A sustainability evaluation based on a life cycle and circular approach is presented and discussed using a simple case study performed at real industrial scale. The lime ash waste from the pulp and paper industry is used to replace 100% of the natural filler used in precast concrete production and the impacts and benefits from the technical, environmental, economic and social level were assessed. It was demonstrated that this simple action causes positive impacts in the evaluated dimensions of sustainability without causing any changes in production time and causes no degradation on relevant concrete properties.

Concrete precast rejects – treatment, characterization, and application in new concrete as recycled aggregate

This article evaluates the feasibility of using concrete waste from precast production as recycled aggregate in concrete. The processing of concrete waste employed a jaw-hammer crusher and a sieve, producing three types of Recycled Concrete Aggregate (RCA). After their characterization, RCA was incorporated in two types of concrete used in the precast factory: a flowing concrete (FC), slump 220 mm, employed in columns and beams; and the second one, a no-slump extruded concrete (NSC), used for hollow core slabs. X-Ray diffraction, thermogravimetric analysis and scanning electronic microscopy showed phases from the hydrated cement paste and the original aggregate. Results of mechanical performance showed that RCA did not influence the compressive strength but influenced other properties such as water absorption and modulus of elasticity. Lastly, it was concluded that RCA obtained in the precast factory showed great potential to be used within the factory production process.

Optimized flowshop scheduling for precast production considering process connection and blocking

Precast production scheduling is a key issue in prefabricated construction. Process connection and blocking are two characteristics of the flowshop production of precast components; however, they have received little attention in research on production scheduling, which may prevent actual production from following optimized scheduling schemes. In this study, an optimization model for the production scheduling of precast components was established considering process connection and blocking for minimizing the total penalty cost of earliness and tardiness. A solution for the model was designed and applied to a practical case for validation. The results indicate that the improved scheduling scheme can reduce the penalty cost and facilitate on-time delivery of precast components under two scenarios: tardiness partially allowed and no tardiness allowed. The proposed model and method can help precast plants to improve efficiency and reduce cost in addition to enhancing the practicality of precast production scheduling schemes.

Shear Vibration Equivalent Method for Determining Vibration Frequency of Concrete Prefabrication Production

In order to solve the problem of determining the process parameters caused by the rheological property of concrete in the industrialized vibration compaction production, the shear vibration equivalent method for determining the vibration frequency of concrete prefabrication production is proposed. According to the equivalent effect of shear and vibration, the particle flow interaction theory is used to calculate the rheological parameters of cement paste in the flow field of rotary viscometer under vibration. The mapping relationship between vibration frequency and shear rate can be established when the amplitude is fixed. The apparent viscosity can be used as the evaluation index of the fluidity of concrete mixture in rheology. By studying the critical point of the influence of shear rate on the decrease of apparent viscosity of concrete mixture, the optimal shear rate which can make the apparent viscosity decrease to the limit value is obtained. Combining with the optimal shear rate and the mapping relationship between vibration frequency and shear rate, the optimal vibration frequency of concrete precast production can be determined. This method can be applied to the quantitative determination of vibration frequency in the vibration compaction production of precast concrete components, which is conducive to the improvement of product performance and control of energy consumption cost.

Material Risk Pooling: Strategies for Precast Fabrication

Materials used in precast fabrication are different from those cast in the construction site. When fabricators lack production materials, they have to await the materials until the supplier transports them to the precast fabricator. The primary objective of the study is to enhance on-time delivery with relatively low inventory by leading risk-pooling concept with lateral transshipment strategy. To achieve the goal, this research develops lateral transshipment strategies by considering the characteristics and requirements of precast production. The computer simulation technique is then used to analyze the material risk pooling strategies. The proposed method can be used to analyze optimum transshipment policy for shipping the required materials from manufacturing plants that have surplus to others starving for materials. Risks of late delivery can thus be reduced.

Early age activation of slag concrete for applications in hollowcore slabs

Prestressed hollowcore slabs are potentially critical segments in the construction sequence of a precast concrete structure, in which very early age strength is vital for ensuring factory productivity. Importantly, the construction industry is striving to reduce concrete's carbon footprint by using Portland cement substitutes, particularly using ground granulated blastfurnace slag (GGBS) in Ireland. This paper investigates the early age strength enhancement methods for slag-concrete mixes, in order to address the well-known retarding effects arising from slag's inclusion. The strength enhancement methods, including temperature curing and a novel accelerating admixture, are used to activate the slag in the concrete mixes, with replacement rates up to 50% GGBS. The efficacy of these methods is investigated in relation to establishing the development of compressive strength and modulus of elasticity over time (being relevant to stress transfer), particularly at very early and at later ages for strength compliance. The study demonstrates the potential for using up to 50% GGBS mixes for slab production while still maintaining the strengths sufficient to achieve existing productivity targets in precast concrete production.

Hybrid Rescheduling Optimization Model under Disruptions in Precast Production Considering Real-World Environment

Increased emphasis is currently placed on precast production scheduling due to the upward-trending applications of precast technology. However, existing studies primarily focused on static scheduling, and few of them addressed dynamic rescheduling problems subject to disruptions from individual products without considering constraints in the practical environment. In this paper, a hybrid rescheduling optimization model for precast production is proposed to minimize rescheduling costs and ensure on-time delivery under disruptions of machine breakdown. The rescheduling was first optimized based on the genetic algorithm considering the idle time of multiple production lines, time intervals, and operation characteristics in precast production. Subsequently, the feasibility of potential reschedules was further verified via simulating production uncertainties in a real-world environment to achieve a trade-off between a high service level and profit maximization. Finally, a case study with different realistic scenarios was conducted to prove the superiority of the model in comparison with other methods. This methodology will increase the applicability of rescheduling methods in practice and reduce production costs of components in precast construction.

Just-in-time scheduling for a distributed concrete precast flow shop system

This paper focuses on the distributed concrete precast flow shop scheduling problem to minimize total weighted earliness and tardiness. It is crucial for a precast manufacturer to schedule jobs effectively to meet shipping dates because of tight due date, limited inventory capacity and huge tardiness penalties. In order to respond quickly to customer demands, many concrete precast manufacturers have adopted the distributed-multiple-factory mode in which job assignment and scheduling have to be decided jointly. To solve this problem, through analyzing the characteristics of distributed precast production, we first develop a novel mixed integer nonlinear programming (MINLP) model and then transform it into an effective mixed integer linear programming (MILP) model by linearization techniques. Additionally, since the problem is more complex than the classical distributed flow shop scheduling problem, which is NP-hard in most cases, we propose a hybrid iterated greedy algorithm (HIG) by integrating due date related NEH-based heuristics, problem-specific knowledge, different local search methods, and mechanism of destruction and reconstruction. Subsequently, we propose a hybrid tabu search and iterated greedy (HTS_IG) in which a hybrid tabu search (HTS) is run at first and then an iterated greedy (IG) starts from the best solution obtained by HTS. Aimed at improving search efficiency, some structural properties of the schedules are explored and integrated into the local search steps of HIG and HTS_IG. We also develop a hybrid genetic algorithm and variable neighborhood search (HGA_VNS) and a two-phase heuristic method (TPHM) for comparison. Finally, extensive experiments and deep analysis are conducted on instances with different combination of problem parameters. Computational results show the effectiveness of the MILP model and the proposed algorithms. The computational analysis indicates that, on average, HTS_IG performs best among all the proposed metaheuristics. The effectivenesses of local search based on problem-specific knowledge (PSK) in HIG and HTS_IG are also verified.

Hollowcore slab with alternative cementitious materials for winter conditions

The precast industry, due to its specific early-age strength requirements for hollowcore (HC) slab products, has been reluctant to introduce alternative cementitious materials such as ground granulated blast-furnace slag (GGBS) due to the slower strength development of such materials. This paper reports on a study undertaken at a precast production facility to examine how to overcome the consequences of strength loss due to the replacement of up to 50% of CEM I (42·5R), as usually used in cold weather conditions, with GGBS, for environmental or durability reasons. The GGBS concrete slabs were activated using thermal, chemical and mechanical means to enhance their early-age strength gain. The results were compared at early ages in terms of the temperature profile during curing, cube compressive strengths, load-carrying capacities for transportability requirements, ultimate load and short-term creep. In addition, 28 d densities and strengths were compared for in situ cubes and cores extracted from HC slab samples. The experimental results showed a favourable potential for replacing CEM I (42·5R) cement with up to 50% GGBS in winter without compromising on factory productivity.