Key Engineering Materials Vols. 348-349

Abstract: It is well known that PC (polycarboxylate) agent is superior to other agents for the early-strength of concrete. Thus, this study investigates the development of mortar strength using various agents. To prove this, various factors were tested. Furthermore, this study measured compressive strength at the age of 18, 24, 36, 72, and 168 hours and gave a request text TG/DTA to observe minute structures. In addition, this study took pictures of minute structures using an SEM for each agent at the same age. According to the results, mortar using an early-strength PC agents is faster than a general water reducing AE agent, high performance PC agents, and other agents in the acceleration of hydration at the same early age. A TG/DTA test shows that the early-strength PC agents create more hydration products, such as Ca(OH)2, than others at the same age. The degree of pH in each agent is unrelated to the degree of hydration in mortar. An MIP analysis confirms these results. However, other methods are required the exact analysis of micro structures.

Abstract: Recently, Reinforced Concrete(RC) is used in most buildings. However, steel bars in concrete cause corrosion through carbonation. Furthermore, corrosion shortens the life span of RC structures. Therefore, the surface-finishes such as restraint for penetration and diffusion of CO2 were used to lengthen the life span of RC structures. This study attempted to verify the restraining effect on a carbonation job according to the applied surface-finishes using an FEM analysis. This study also evaluated the restraining effect of carbonation on other surface-finishes with the process proposed in this study.

Abstract: In this study, accelerated corrosion tests were conducted on concrete specimens with and without accelerated carbonation beforehand for the purpose of elucidating the effects of carbonation, cover depth, and water-cement ratio (W/C) on the reinforcement corrosion. During testing, the corrosion current between the anode steel and cathode stainless steel was measured to continuously monitor the progress of corrosion throughout the test period, thereby investigating the mechanism of reinforcement corrosion and the relationship between corrosion and crack width, as well as other parameters.

Abstract: A cement which is used in construction and a concrete which is a hydration product of cement is considered anti-environmental materials because of lots of CO2 emission in progress of producing and making them. But a concrete absorbs CO2 gas in atmosphere after hydration and in its lifetime. It is called carbonation. Based on Papadakis’ theses, this research is carried on calculation of the CO2 absorption quantity in concrete. After research, we calculated the CO2 absorption quantity in concrete which has various surface-finishes and we evaluate each surface-finishes the resistance against carbonation.

Abstract: This study investigated the residual strength of aluminum alloy sheet with multiple site damage (MSD) through three types of aluminum specimens test. Aluminum panels with bare collinear constant diameter holes were chosen as specimens. And there were saw cuts at both edges of all the holes. After some constant amplitude tension-tension load cycles, the MSD were found in these specimens since there were multiple fatigue cracks emanating from the saw cuts of holes. The residual strength was recorded as the maximum load when every specimen was subjected to monotonically increasing tensile load until failure occurred. The test results were compared with predicted residual strength results by five different failure prediction criteria that were often used in engineering in order to evaluate the accuracy of these criteria. The failure criteria included: fracture criterion, net ligament loss criterion, ligament yield criterion, CTOA/CTOD criterion and average stress criterion. Ligament yield criterion (Swift criterion) and average stress criterion got more accurate prediction results than other criteria.

Abstract: Full-scale burst test data of high-grade line pipes for high-pressure gas pipelines were referred to, and 3-D elastic-plastic finite element analysis was carried out using the test data for the calculation of fracture parameters. Ductile crack initiation was evaluated by the intersection of a toughness locus and a crack driving force curve, where the toughness locus was indicated by the relationship between the critical equivalent plastic strain and the stress triaxiality, and the crack driving force curve was shown by a history of the equivalent plastic strain and the stress triaxiality at characteristic distance. In addition, ductile crack rapid propagation was assessed by the relationship between the critical CTOA and the global constraint factor, where the critical CTOA remained almost constant because of high constraint.

Abstract: The non-linear crack mechanics (NLCM) is a concept assuring the occurrence of the same phenomena in two cracked bodies under large scale yielding. It has been recognized that NLCM is effective in the cases of plane stress conditions. In this study, it was made clear that NLCM is effective not only in the case of plane stress condition but also in the case of plane strain condition.

Abstract: A multilayer medium consists of compacted soil, gravel and concrete layers. The damage law of multilayer mediums subjected to blast loading is investigated numerically at various charge weights ranging from 1 to 10kg and burying depths ranging from 0 to 150cm. The numerical results indicate that, in order to increase the energy utilization rate of explosives, charges less than 5kg should be placed in the gravel layer to explode, while those more than 5kg placed in the compacted soil layer. By use of dimensional analysis, the formula for damage effect of multilayer mediums subjected to blast loading is consequently derived. Based on regression analysis of the numerical results, the empirical expressions are established for the effects of charge weights and burying depth on the crater radiuses in the concrete layer, the gravel layer and the compacted soil layer. The expressions can be employed to assess the damage effect of charges blasting in multilayer mediums.

Abstract: Due to its importance to the durability assessment of reinforced concrete structures located in a marine or de-icing salt environment, it is essential to determine the chloride diffusivity of concrete. This paper presents a numerical method for predicting the chloride diffusivity of concrete with interfacial cracks. By modeling concrete as a three-phase composite material composed of aggregate, interfacial transition zone and cement paste, a composite circle model with an interfacial crack located on the aggregate surface is constructed. The finite element method is used to solve the composite circle under a given boundary condition and the chloride diffusivity of concrete is then determined numerically. After verifying the numerical method with experimental results obtained from the literature, the effect of interfacial cracks on the chloride diffusivity of concrete is evaluated in a quantitative manner. It is found that the chloride diffusivity of concrete increases with the increase of the subtended angle of interfacial cracks. The paper concludes that the numerical method presented in this paper can predict the chloride diffusivity of concrete with reasonable accuracy.

Abstract: The microbiological influenced corrosion (MIC) behavior of the low alloy steel with or without Zn-rich epoxy coating in the sterilized medium and sulfate-reducing bacteria (SRB) solution was investigated with electrochemical impedance spectroscopy (EIS), scanning electron microscope (SEM) and X-rays diffraction (XRD). Results show that the bacteria in the marine environment affect the corrosion behavior of the ship plate steel and the corrosion resistance of specimen coated with Zn-rich epoxy was improved greatly. The coating protected the test steel effectively in the microbial environment with the cathodic protection in the earlier period and physical barrier protection in the later period.