Key Engineering Materials Vols. 488-489

Abstract: Since ultra-high performance cementitious composite (UHPCC) exhibits remarkable compressive strength and ductility, its application for structural member provides significant reduction of the section. The use of low water-to-binder ratio and admixtures with high fineness induce large shrinkage strain, leading to the possibility of large occurrence of shrinkage cracks due to the restraints of the form and reinforcing bars. Therefore, this study admixes a combination of expansive and shrinkage reducing agents as a solution to reduce the shrinkage of UHPCC. The eventual appropriateness is computed to evaluate the free shrinkage and restrained shrinkage behaviors. From the test results, the admixing of a combination of expansive and shrinkage reducing agents is seen to achieve a reduction of the free shrinkage by 30% to 50% at 28 days and a reduction of the strain of the external steel by about 19%.

Abstract: Concrete materials with a large number of micro-cracks were defined as inhomogeneous materials. And the mechanical properties of inhomogeneous materials were regarded as high-order deformation gradient dependent. Starting from the nonlocal thermodynamics theory and the hypothesis of total energy equivalence, the gradient-dependent nonlocal damage constitutive models of concrete under freeze-thaw action would be established in this paper.

Abstract: In the present study, the rare earths element YbCl₃ was added into the Zn-epoxy coating, and the MIC behavior of the low alloy steel specimen with YbCl₃-Zn-epoxy coating in the sulfate-reducing bacteria (SRB) solution was investigated and compared with the specimen of Zn-epoxy coating. Experimental results show that both the YbCl₃-Zn-epoxy and Zn-epoxy coating may offer effective protection for the basic low alloy steel. However, the corrosion potential of the specimen with YbCl₃-Zn epoxy coating was obviously higher than the Zn-epoxy coating, suggesting that the YbCl₃-Zn-epoxy coating may offer more favorable protection. Results of X-rays diffraction (XRD) and surface micrographs of specimens show that more sulfides and corrosion products of YbCl₃-Zn-epoxy coating were produced which increased the shielding property of the coating. The mechanism about the effect of YbCl₃-Zn-epoxy coating on MIC behavior was further discussed.

Abstract: The MIC behavior of the ship plate steel specimen with LaCl₃-Zn epoxy coating in the sulfate-reducing bacteria (SRB) solution was investigated in this paper. The variation of corrosion potential over time of different specimens in SRB solution show that the corrosion potential of the specimen with LaCl₃-Zn epoxy coating was obviously higher than the Zn-epoxy coating, suggesting that the LaCl₃-Zn epoxy coating may offer better protection. The variations of lgflg |Z|=4.5 and f_h with time show that the property of anti-infiltration and corrosion resistance of LaCl₃-Zn coating is much better than the ones of Zn-epoxy coating. Results also show that more sulfides and corrosion products of LaCl₃-Zn epoxy coating were produced which increased the shielding property of the coating. The experimental results of XRD and SEM are in good agreement with the ones of E_corr, and EIS, etc. They all show that the LaCl₃-Zn epoxy coating exhibits more favorable corrosion resistance property than the Zn-epoxy coating. It is obvious that coating the ship plate steel with LaCl₃-Zn epoxy is an effective and promising method against the attack of SRB in marine environment.

Abstract: The computational analysis of an all fracture modes (AFM) specimen on mixed-mode I+II+III fracture is presented in this paper. The separated energy release rates (SERRs) along the crack front of the AFM-model are calculated by the modified virtual crack closure integral (MVCCI)-method and the commercially available software ANSYS. A transition model is built by adopting several 3D elements of SOLID45 and one point element of MASS21 in the ANSYS program. Under the related constraint conditions, the separate force and moments are respectively applied on the point element of the transition model, so the corresponding desired reaction forces can be obtained. When the desired loads are superimposed and applied on the AFM-model, the mixed-mode I+II+III fracture can then be achieved. Thereby, the SERR results are calculated. The calculation results show that the facture behavior of G_II and G_III appears complex due to the global deformation and Poisson’s ratio, although the distribution of SEERs G_I is symmetrical with respect to the middle point along the crack front. The total SERRs, G_Tn-values increase along the crack front with the minim value at one corner and the maxim value at the other corner. It can therefore be predicted that the fracture will occur initially at one corner on the crack front of the AFM-specimen in this case.

Abstract: The microbiological influenced corrosion (MIC) behavior of the low alloy steel with granular-Zn-epoxy and flaky-Zn-epoxy coating in the sulfate-reducing bacteria (SRB) solution was investigated with electrochemical impedance spectroscopy (EIS), X-rays diffraction (XRD), scanning electron microscope (SEM) etc. Results show that the protection effect of the flaky-Zn coating specimen is much better than the granular-Zn coating one. The dissolution of zinc is more severe in granular-Zn coating than in flaky-Zn coating when the specimen immersed in the SRB solution. The shielding property of flaky zinc is much higher than granular zinc in the coating. The flaky-Zn coating is much more compact than the granular-Zn coating and therefore the property of anti-infiltration is much better. We may conclude that the flaky-Zn coating exhibited more favorable corrosion resistance property than the granular one.

Abstract: In this paper, the computational predictions of crack initial breakpoint and deflection angles under bend and torsion loading conditions are investigated in conjunction with the modified virtual crack closure integral (MVCCI)-method by using the all fracture modes (AFM) specimen and commercial software ANSYS. The separated strain energy release rates (SERRs) along the crack front are calculated and subsequently converted to the stress intensity factors (SIFs) by using Irwin´s equations. Based on the SIFs results, the crack initiation predictions are presented by the maximum principal stress σ₁^'-criterion. Results show that when the AFM-model under a series of combined proportional bend and torsion loading conditions, asymmetrical stress fields are produced along the crack front. The presented investigation also shows that the maximum principal stress σ₁^'-criterion in conjunction with the MVCCI-method provides a powerful numerical tool for general computational approach to the fracture analysis of complex loading conditions.

Abstract: With progress of the computer technology and numerical simulation method, the numerical simulation of the fracture process of concrete materials has become possible. In this paper, the numerical simulation models of the two types of samples were carried out with the SOLID65 concrete element based on the ANSYS software platform. According to the results, the non-linear characteristic of the concrete material exhibited in the loading process is reflected by the phenomenon that the slope of the later stage shows some reduction in the simulated load - loading point displacement curve. That is to say, the behavior of the appearance and development of cracks can be simulated with SOLID65 concrete element in ANSYS.

Abstract: Ultra-high performance concrete (UHPC) is a new generation of concrete developed through microstructure enhancement techniques for cementitious materials. UHPC exhibits extremely high compressive and flexural strengths exceeding 180 and 30 MPa, respectively, and remarkable durability compared to normal concretes. The fabrication of UHPC requires very low W/B ratio reaching merely 0.2, the use of large quantities of fine binder and superplasticizer without coarse aggregates, and the incorporation of steel micro-fibers. This study investigates the effect of the type of silica fume on the rheological and mechanical properties of UHPC. The adopted silica fume presents various contents of SiO₂ and surface areas. From the experimental results, UHPC using silica fume with 94% of SiO₂ 3% of ZrO₂, and surface area of 80,000 g/cm³ shows better flowability than UHPC using silica fume with 98% of SiO₂ and surface area of 200,000 g/cm³ by lowering the viscosity of the cementitious composites without decreasing the compressive strength. Therefore, the fabrication cost of UHPC can be reduced by smaller dosage of superplasticizer when using silica fume with Zr content .

Abstract: To replace bottom ash for natural sand completely, the mix proportions of bottom ash in concrete was adjusted according to tab density and replacement ratio of polymeric resin/Potland cement(PC) were established. And then testing for slump, setting time, and compressive strength was conducted. According to test results, the compressive strength of concrete using the bottom ash was lower than that of concrete using natural sand (BA0 concrete). But by adjusting the amount of bottom ash in concrete according tab density so that the fine aggregate proportions change 44% to 38%, the compressive strength of concrete using the bottom ash could even be higher than BA0 concrete. And as the polymeric resin content of bottom ash concrete increased, strength would be increased drastically, but proper dispersant should be cooperated with polymeric resin cement with fine bottom ash powders.