The recycled fine-powder (RFP), produced during the recycling process, will induce a serious impact on the environment with improper disposition. A potential green way to reuse RFP is to add it as ...supplementary cementitious material in concrete. The effects of RFP on the hydration, microstructure, shrinkage and mechanical properties of ultra-high performance engineered cementitious composites (UHP-ECC) with different replacement ratios up to 50% were investigated. The hydration kinetics were compared among the different replacement ratios using the isothermal calorimetry, which demonstrated an accelerating effect of RFP to the hydration of UHP-ECC matrix. The phase development was quantified by the thermal gravimetric analysis and proved the pozzolanic effect of RFP. The compressive and tensile properties of UHP-ECCs were obtained at 3, 7 and 28 days, respectively, to trace their development along the curing ages. The addition of RFP significantly reduced the autogenous shrinkage of UHP-ECC. Besides, the single fiber pullout test was investigated to quantify the influence of RFP at the fiber level. The environmental scanned electron microscope analysis was conducted to study the morphology of PE fiber at the fracture surface.
•Up to 50% of cement was replaced by recycled fine powder (RFP) without significant loss in mechanical properties•Effects of RFP on the hydration, microstructure, shrinkage and mechanical properties of UHP-ECC were investigated•A linkage of micro-mechanical scale at the fiber level and to macro-mechanical scale at the composite level was established.
•Total flowtime minimization for the distributed permutation flowshop is addressed.•Three novel heuristics are presented to obtain good results in a few minutes.•Four effective metaheuristics are ...proposed to further improve the quality of solutions.•Problem-specific knowledge and accelerations to evaluate neighboring solutions are explored.•Experimental results show that the presented methods significantly outperform the existing algorithms in the literature.
Distributed permutation flowshop scheduling problem (DPFSP) has become a very active research area in recent years. However, minimizing total flowtime in DPFSP, a very relevant and meaningful objective for today's dynamic manufacturing environment, has not captured much attention so far. In this paper, we address the DPFSP with total flowtime criterion. To suit the needs of different CPU time demands and solution quality, we present three constructive heuristics and four metaheuristics. The constructive heuristics are based on the well-known LR and NEH heuristics. The metaheuristics are based on the high-performing frameworks of discrete artificial bee colony, scatter search, iterated local search, and iterated greedy, which have been applied with great success to closely related scheduling problems. We explore the problem-specific knowledge and accelerations to evaluate neighboring solutions for the considered problem. We introduce advanced and effective technologies like a referenced local search, a strategy to escape from local optima, and an enhanced intensive search method for the presented metaheuristics. A comprehensive computational campaign against the closely related and well performing algorithms in the literature is carried out. The results show that both the presented constructive heuristics and metaheuristics are very effective for solving the DPFSP with total flowtime criterion.
A systematic study of the basic mechanical properties of ultra-high ductility cementitous composites (UHDCC), including the compressive, tensile and shear properties from normal strength to high ...strength were investigated in present research. The compressive strength of cylinder specimens with diameter of 100 mm and height of 200 mm were in the range of 43–115 MPa. The compressive strain corresponding to the peak stress, the Young’s modulus and the Poisson’s ratio were calculated. The tensile properties including the peak stress, the strain capacity and the strain energy were obtained as well as the relationships between the aforementioned parameters and the compressive strength. The peak tensile stress and the strain capacity of UHDCC were ranged from 6.2 MPa to 16.5 MPa, and 8.0% to 11.1%, respectively. Additionally, the shear stress-strain curves and the relationship between the shear strength and the corresponding compressive strength were also established. During the whole loading process of direct tensile and shear tests, the crack patterns were monitored by digital image correlation method.
AbstractThis research developed an ultra-high-performance engineered cementitious composite (UHP-ECC), which combines the properties of strain-hardening, multiple cracking, and high mechanical ...strength. The compressive strength of the UHP-ECC reached 150 MPa at 28 days under standard curing conditions, whereas the tensile strength and strain capacity of the UHP-ECC were 18 MPa and 8%, respectively. Different fiber volumetric ratios and geometries (fiber length and diameter) were used to investigate the influences of fiber-reinforcement parameters on the mechanical and crack-pattern properties of UHP-ECC, including the tensile strength, strain capacity, strain energy, crack number, and crack spacing. It was found that the fiber reinforcement parameters significantly influence both the mechanical properties and crack-patterns of UHP-ECC. Based on the test results, a bilinear tensile stress–strain model was proposed for UHP-ECC and its accuracy was demonstrated through comparisons with the test results.
•The tensile, compressive and flexural behaviors of UHP-ECC were systematically investigated.•UHP-ECC combines the strain-hardening and multiple crack characteristics and the high strength of mortar ...matrix.•Ultra-high-molecular-weight polyethylene (PE) fibers with a high aspect ratio were deployed.•The digital image correlation (DIC) technique was utilized to monitor the crack patterns during the tests.•Scanning electron microscope (SEM) analysis was conducted to understand the microstructure of UHP-ECC.
Ultra-high performance engineered cementitious composites (UHP-ECC), which combines the strain-hardening and multiple crack characteristics and the high strength of mortar matrix, was investigated in this study. The tensile strength and elongation of the UHP-ECC achieved were 20 MPa and 8.7%, respectively. For the production of UHP-ECC, ultra-high-molecular-weight polyethylene (PE) fibers were deployed to reinforce the ultra-high strength mortar while special attention was paid to the mix process to ensure satisfactory fiber dispersion. The tensile stress-strain curves, the compressive strength and elastic modulus, and the flexural behavior of UHP-ECC were investigated to understand its mechanical performance. The digital image correlation (DIC) technique was utilized to monitor the crack patterns of UHP-ECC during the tensile and flexural tests. In addition, Scanning electron microscope (SEM) analysis was conducted to achieve an in-depth understanding of the microstructure of UHP-ECC.
•An ultra-high performance engineered cementitious composites was developed.•Flexural and shear behaviors of reinforced UHP-ECC beams show superior performance than RC beams.•Feasibility of utilizing ...UHP-ECC to largely reduce steel bar in structural member was proved.
The structural behaviors of steel reinforced ultra-high performance engineered cementitious composites (UHP-ECC) beams under bending were experimentally explored and compared to the ordinary reinforced concrete (RC) beams in present research. Two series of beams, reinforced or unreinforced with stirrups, were prepared to study the flexural and shear performance of steel reinforced UHP-ECC (RU) beams. The UHP-ECC was featured with the tensile strength of 16 MPa and the tensile strain capacity around 8%. The steel reinforcement ratios of longitudinal bar for both RU and RC beams were 0.69%, 1.86% and 2.94%, respectively. The crack propagation and the failure mode of RU and RC beams were monitored by digital image correlation (DIC) method. Additionally, the load-displacement relationships, the ductility index values and the component strains including steel bar and UHP-ECC of RU beams were obtained and compared with RC beams. It was found that the RU beams showed superior performance in both load capacity and ductility at the ultimate limit state; while the crack width and deflection at the serviceability limit state of RU beams were much smaller than those of RC beams. The loading capacity of non-steel reinforced UHP-ECC (NU) beams was approaching to the one of RC beams with reinforcement ratio of 1.86%, which indicated the feasibility of utilizing the UHP-ECC to substantially reduce or replace the steel bar in structural members.
This paper proposes a total of nine algorithms to minimize the makespan for the hybrid flowshop scheduling problem with sequence-dependent setup times. The first six algorithms are trajectory-based ...metaheuristics, including three variants of iterated local search and three variants of iterated greedy. The remaining three algorithms are population-based metaheuristics, namely, the improved fruit fly optimization, the improved migrating birds optimization, and the discrete artificial bee colony optimization. We present some advanced and effective technologies, including three mixed neighborhood structures, an enhanced perturbation method, and an enhanced destruction and construction procedure for the trajectory-based metaheuristics. We propose a path-relinking-based cooperative search, a diversity control scheme, and a diversified initialization approach for the improved fruit fly optimization. We calibrate the parameters and operators for the proposed algorithms by means of a design of experiments approach. To evaluate the proposed algorithms, we present several adaptations of other recent well-known meta-heuristics for the problem and conduct a comprehensive set of computational and statistical experiments to demonstrate the effectiveness of the presented algorithms. Among them, the discrete artificial bee colony optimization is the best-performing algorithm and it is able to improve 126 out of the 240 best known solutions for the benchmarks in the literature.
This paper investigates the flexural performance of a series of RC beams externally bonded with carbon fiber-reinforced polymer (CFRP) grid-reinforced engineered cementitious composite (ECC) matrix. ...A total of 15 RC beams, including three control and twelve strengthened, were prepared and tested. The test variables included the longitudinal reinforcement ratio, the strengthening configurations that consisted of different cementitious matrices (ECC versus epoxy mortar), different installation methods (prefabricated versus cast-in-place), and different stiffness of CFRP grids. The test results showed that ECC is an ideal cementitious matrix for the strengthening applications where FRP grids are used as the external reinforcement. The flexural strengthening configuration using the epoxy adhesive to bond prefabricated CFRP grid-reinforced ECC plate proved to be the most efficient solution. For such configuration, the plate-end debonding can be avoided and the mid-span debonding can be almost suppressed. Flexural capacity analysis was conducted and demonstrated that the plane section assumption is valid and the full strength composite action can be nearly achieved for the strengthening system. The average ratio of the predicted peak loads to the experimental ones of the strengthened RC beams was 1.05.
This paper addresses a novel distributed assembly permutation flowshop scheduling problem that has important applications in modern supply chains and manufacturing systems. The problem considers a ...number of identical factories, each one consisting of a flowshop for part-processing plus an assembly line for product-processing. The objective is to minimize the makespan. To suit the needs of different CPU time and solution quality, we present a mixed integer linear model, three constructive heuristics, two variable neighborhood search methods, and an iterated greedy algorithm. Important problem-specific knowledge is obtained to enhance the effectiveness of the algorithms. Accelerations for evaluating solutions are proposed to save computational efforts. The parameters and operators of the algorithms are calibrated and analyzed using a design of experiments. To prove the algorithms, we present a total of 16 adaptations of other well-known and recent heuristics, variable neighborhood search algorithms, and meta-heuristics for the problem and carry out a comprehensive set of computational and statistical experiments with a total of 810 instances. The results show that the proposed algorithms are very effective and efficient to solve the problem under consideration as they outperform the existing methods by a significant margin.
•This is the first study of a distributed assembly permutation flowshop problem.•A total of seven algorithms are presented.•A set of formulas to accelerate the computation are proposed.•The presented algorithms perform much better than 16 algorithms in the literature.
Distributed Permutation Flowshop Scheduling Problem (DPFSP) has become a research hotspot in recent years. However, as a service level objective, the Total Weighted Earliness and Tardiness (TWET) has ...not been addressed so far. Due to the importance of the service level objective in modern industry, we deal with the minimization of the TWET for the DPFSP with due windows . An Iterated Greedy (IG) algorithm, namely IG with Idle Time insertion Evaluation (IGITE), is proposed. In the algorithm, an adapted NEH heuristic with five rules based on the unit earliness weight and unit tardiness weight, the due date, and the smallest slack on the last machine is used to generate an initial solution. Destruction procedure with a dynamic size is provided to enhance the exploration capability of the algorithm. Idle time insertion method is utilized to make the completion time of jobs within the due windows or as close to the due windows as possible. A large number of experiments show that the presented algorithm performs significantly better than the five competing algorithms adapted in the literature. The performance analysis shows that the IGITE is the most appropriate for the DPFSP with due windows among the tested algorithms.
•The first study of distributed permutation flowshop scheduling with due windows.•An effective Iterated Greedy algorithm is proposed.•Three rules are proposed for adapted NEH heuristic to generate initial solution.•Destruction with dynamic size is provided to yield more diverse search areas.•Idle time insertion method is used to complete jobs within or near due windows.
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