High pH nature of concrete microstructure can lead to chemical interaction between reactive silica in aggregate and alkali species in pore solution. As a result, alkali silica gel is rendered which can cause distress in hardened concrete. However, the consequence of silica dissolution is not only the gel formation and damage in cement paste, but also significant weakening of the reactive aggregate itself. In this study, three highly reactive, well-documented concrete aggregates were investigated. The aim was to characterize the micromechanical and -morphological alterations of the aggregates under aggressive alkaline solution by means of microscopy and nano-indentation techniques. It was found that silica dissolution alters micromorphology of the reactive aggregates and reduces elastic modulus and hardness values significantly.
A new inspection technique that uses near-infrared spectroscopy is focused on as a method for detecting the chloride ion content in concrete structures. The authors have been working to confirm the possibility of estimating comparatively easily the chloride content in concrete without chemical analysis and in a short time on site. In this study, mortar specimens deteriorated by the combination of chloride attack and carbonation were prepared for investigating the method of evaluating the chloride ion content in mortar with the near-infrared spectroscopic technique. As a result, it was found that the chloride ion content in a carbonated mortar specimen can be evaluated with a method similar to that used to detect deterioration due solely to chloride attack.
The effect of loading on chloride penetration into concrete is evaluated in this study. It is found that the chloride penetration rates for OPC concrete and blast furnace slag BFS concrete under the tensile stress were increased by 29% and 77%, respectively. The diffusion coefficient of BFS concrete was lower than that of conventional concrete without BFS, no loads and stress states. Under tensile stress, the diffusion coefficient for BFS and plain concrete showed higher values with increasing stress. The influence of specific surface area on the diffusion coefficient was investigated. As a result, the larger the specific surface areas of BFS are the lower diffusion coefficients. This tendency was more pronounced under the high stress conditions. The diffusion coefficient was found to decline with increases in the ratio of substituted BFS. This result was the same even under the tensile stress conditions. The chloride penetration depth was distributed uniformly when no stress was applied. However, in the case of tensile loading, the diffusion depth was not distributed uniformly, and showed prominent characteristics. This result indicates that analysis using average values of chloride penetration depth is not proper under load conditions.
In this paper the response of composite structural elements cast against thin-walled stay-in-place (SiP) formwork elements made of Textile Reinforced Concrete (TRC) is experimentally investigated and analytically approached. TRC comprises an innovative composite material consisting of fabric meshes made of long fibre yarns (e.g carbon, glass, aramid or basalt) arranged in at least two (typically orthogonal) directions and embedded in a cementitious fine-grained matrix. Two types of reinforced concrete specimens were considered: the first one included 22 beam-type specimens incorporating flat TRC formworks, whereas the second included 11 prismatic column-type specimens cast into permanent precast TRC shafts. Moment and deflection values at first-crack, steel yielding (where applicable) and ultimate for the beam-type specimens were analytically derived based on a proposed simplified approximation of strain distribution across a fibre roving. Based on the results of this study SiP TRC formwork elements comprise an attractive system for hybrid construction practices.
Ultra High Performance-Strain Hardening Cementitious Composites (UHP-SHCC) are a composite material comprising a cement-based matrix and short fibers with outstanding mechanical and protective performance. Surface protection repair using a thin layer of UHP-SHCC to extend the service life of concrete structures has been proposed, and surface protec-tion performance associated with both a durable matrix and multiple fine cracks is required. This paper presents an ex-ample of decreased cracking ability and decreased strain capacity in UHP-SHCC specimens of a practical size. Note that, the small size dumbbell-shaped UHP-SHCC specimen can exhibit a large number of cracks and higher strain capacity. Also, this paper assesses the usage of a small amount of steel reinforcement in order to enhance the crack distribution and strain capacity of practical size UHP-SHCC specimens in tension. Practical-size specimen dimensions (cross sectional size: 200 x 50mm), which are similar to the typical size used for surface protection repair applications (depth of 30 to 70 mm), were selected in this study. Different reinforcement ratios ranging from 0.3% to 1.2% were used to evaluate the effect of the reinforcement ratio on the specimens' strain capacity and crack distribution.
This paper discusses the pre- and post cracking behavior and tensile response of concrete panels subjected to axial tension. The main objective of this investigation is to study the stress-strain relationship of thick reinforced concrete plates, taking into consideration the effect of the steel reinforcement in both directions, as the thick concrete panels are well used in offshore concrete structures and nuclear power plant construction. A theoretical model for predicting the cracking behavior, which includes the crack spacing and width of reinforced concrete panels under axial loading at any given loading stage, is developed. In this theoretical model, the main parameters that influence the cracking behavior of concrete in both directions are considered. The behavior of two-way reinforced concrete plate is analyzed with consideration of the effect of concrete tensile strength, reinforcement ratio, bar diameter and spacing in both longitudinal and transverse directions.
Lateral-load resisting systems of many low-rise reinforced concrete (RC) buildings are composed of members that may be vulnerable to pre-emptive shear failures, depending on whether their shear strengths are sufficient to develop their flexural strengths (referred to as dual lateral-load resisting system, subsequently); therefore the buildings have a lateral strength associated with the strengths of the components, and the component strengths may be governed by both shear and flexure (the component strengths are referred to as shear and flexural strengths, subsequently). At present there is no effective ways to assess the component strength and ductility of a RC building having a dual lateral-load resisting system. This paper presents a method for determining required shear and flexural strengths associated with structural damage states for various levels of earthquake demand of low-rise RC buildings having a dual lateral-load resisting system. The interaction curves of the required strengths are derived for various ductility ratios based on nonlinear dynamic analyses of the single-degree-of-freedom system. The structural damage states of RC buildings controlled by both shear and flexure are evaluated in terms of the ductility ratio by the procedure outlined by the Japanese Standard. The proposed method predicts reasonably well damage sustained by actual buildings during an earthquake. The proposed method can be used to develop performance-based seismic evaluation and rehabilitation procedures of low-rise RC buildings having a dual lateral-load resisting system.
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