The incorporation of high performance superplasticizers in concrete is one of the most effective and economic technological methods for achieving sustainable development in the concrete industry. Conventional polyelectrolyte-type superplasticizers have some defects, e.g. poor dispersibility, large slump loss, increasing the shrinkage of concrete and pollution when being manufactured. Although the new generation of comb-like polycarboxylate superplasticizers has remarkable benefits in practice, it also has the shortcoming of low saturation dosage. In this study, based on adsorption-dispersion mechanism of dispersant and polyampholyte solution theory, a new class of amphoteric comb-like copolymer superplasticizer (PACP) was designed and synthesized. The effects of PACP on water reduction, setting, compressive strength, hydration and pore structure were investigated systematically. Results show that PACP can be dosed in small amounts to obtain a water reduction up to 45%. The addition of PACP also does not retard cement hydration and significantly increases the compressive strength of hardened concrete at early and ultimate stages. Moreover, PACP can further improve the rate of heat evolution, delays the time to reach the highest hydration temperature and refines the pore structure of hardened cement paste markedly, leading to decreases of porosity and average pore size.
The second development of ABAQUS is implemented to simulate the initiation, propagation processes of flaws in brittle materials under compressive loading (in the paper ‘flaw’ means ‘the initial crack’, and ‘crack’ means ‘the branch crack’), by which the propagation paths and the corresponding stress intensity factors of the branch crack can be calculated. Further more the experiment is carried out to verify the validity of the above numerical method. By the numerical method, the propagation processes of open flaws and close flaws are simulated, and the comparative analysis of propagation characteristics between the open flaw and the close flaw is carried out. The results show the obvious difference in the propagation characteristics between open flaws and close flaws with the same initial flaw length and angle. Firstly, compared with the close flaw, the branch crack of the open flaw grows along a more obviously curvilinear path, and the propagation path gradually approaches to a line, which passes through the middle point of the open flaw and parallel to the maximum principal stress. Secondly in the early stage of the crack propagation, the stress intensity factors of the branch crack of the open flaw are greater than of the close flaw, but with the further propagation of the branch cracks, the stress intensity factors of the branch crack of the open flaw will be less than of the close flaw. Additionally, according to the close flaw, with the decrease of the friction coefficients, the curve characteristics of the crack propagation paths become more obvious. Therefore, it is noteworthy that the wing crack of the close flaw can be regard as the straight line if the friction coefficient of the flaw surface is very small. The above differences of the propagation characteristics between the open flaws and the close flaw show that the two flaws should be distinguished strictly in the fracture analysis.
This paper proposes an improved HYT (IHYT) approach to achieve better load balance among substructures for better efficiency of the parallel substructure method. In the IHYT method, the matrix ordering method in SPOOLES, which provides the estimated statistics of numerical workload and nonzero entries of the matrix, are employed for predicting the workload of each sub-mesh, and used as the basis for tuning the element weights to embed the workload prediction phase. In addition, a partitioning kernel–JOSTLE, which can slightly tune the partitioning result from the last iteration and is good for the convergence of iterations, are employed as the partitioning kernel. The numerical experiments show that the IHYT further achieves better load balance of substructure condensation and leads to better efficiency of the parallel substructure method than HYT approach.
The stress field around the tip of the blunt crack in rock-type materials under compressive loading is analyzed, and the relation of the stress field is set up. Compared to the stress field of the ideal mathematic crack, the effect on the distribution of the stress field by the thickness or the curvature radius of the blunt crack is considered. Based on the stress field, the two-parameter fracture criterion for the blunt cracks under compressive loading is set up. The two parameters in the criterion are related to the material property, and can be determined by the experiments or theoretical analysis. By the fracture model in the paper, the fracture analysis of the blunt crack under compression are carried out, and the theoretical results are in concordance with the experimental results, which shows the fracture criteria in the paper is available to the fracture analysis of the blunt crack.
Abstract. For the bridge temporary structures, the present mainstream calculation method is based on dialog box data entry or command flow technology, in view of their insurmountable defects, a new calculation method based on graphic flow technology is presented and implemented in this paper. The comprehensive solving process of bridge temporary structure is planed and decomposed into a series of easily implemented sub-steps, their calculation models can be described by a group of independent and cooperative function graphic object types, in which global or local structure features, construction specifications, dynamics characteristics, engineering experience, intention expression, expert solving plan and other comprehensive application knowledge can be expressed easily. By creating, operating and deducting these function graphic objects, the solving sub-steps can be easily implemented. As a result , the comprehensive solving process for bridge temporary structure based on engineering features can be realized , and the simplification and high efficiency of solving process are achieved. The new method is also can be applied to other complex engineering structure fields, development practice shows its broad application prospect and development space.
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