Volume 4, No. 3 Special section:Durability of Concrete Structures edited by Prof. T. Ishida Fracture of Reinforcing Steels in Concrete Structures Damaged by Alkali-Silica Reaction-Field survey, Mechanism and Maintenance-(Invited paper) Toyoaki Miyagawa, Kaoru Seto, Kazunori Sasaki, Yasuhiro Mikata, Kazuhiro Kuzume and Toshikazu Minami Journal of Advanced Concrete Technology, 4(3) 339-355, 2006 Recently, the fracture of reinforcing steels in concrete structures damaged by alkali-silica reaction (ASR) has been discovered in Japan. As long as the reinforcing steels do not get broken due to the expansion caused by ASR, the safety of the structures is considered not to be a serious problem. However, when the confinement of concrete is deteriorated due to the fracture of reinforcing steel bars, it becomes questionable. Therefore, it is important to clarify the mechanism of the fracture of reinforcing steel bars, and to develop the method to detect locations of steel bar fracture and the strengthening methods for concrete structures damaged by ASR. In this paper, firstly, concrete structures damaged by ASR in Kansai area in Japan are introduced to describe the fracture of reinforcing steels. Secondly, results of investigation about fracture mechanism, nondestructive testing methods, repair and strengthening methods for damaged concrete structures are introduced. XRD/Rietveld Analysis of the Hydration and Strength Development of Slag and Limestone Blended Cement Seiichi Hoshino, Kazuo Yamada and Hiroshi Hirao Journal of Advanced Concrete Technology, 4(3) 357-367, 2006 X-ray diffraction (XRD)/Rietveld method was applied to analyze the hydration progress of cement paste prepared with blast furnace slag powder (BFS) and limestone powder (LSP). Rietveld method is able to quantify the amount of amorphous phase as well as crystalline phases. However, in cement paste containing BFS, two kinds of amorphous phases, which are unhydrated BFS and C-S-H, are included and Rietveld method cannot distinguish them. In order to discriminate these tow phases, a selective dissolution method was used to quantify the amount of unhydrated BFS. By combining these two methods, it became possible to quantify the amount of BFS and C-S-H in the hydrated cement.. Analysis results show that BFS accelerates the hydration of C3S, C3A, and especially C4AF. Strength increasing effects of LSP is more eminent in ordinary portland cement (OPC) BFS system than in OPC system. This is attributed to the more amount of calcium aluminate hydrates generation in BFS contained system than in no BFS system. The more calcium aluminate hydrates fill pores and the compressive strength increases. These results show the effectiveness of XRD/Rietveld method as an analysis tool for cement hydration relating to various properties of cement materials. Applications of Electron Probe Microanalyzer for Measurement of Cl Concentration Profile in Concrete Daisuke Mori, Kazuo Yamada, Yoshifumi Hosokawa and Masayoshi Yamamoto Journal of Advanced Concrete Technology, 4(3) 369-383, 2006 Electron probe micro analysis (EPMA) is applied for the quantitative evaluation of Cl ingress into concrete. In order to obtain quantitative data of Cl concentration, the measurement conditions are discussed statistically in detail and an example condition of measurement is introduced. The absolute concentrations of Cl by EPMA are equivalent with wet analysis and the effect of difference of matrix is negligible. By using the difference in chemical compositions between cement paste and aggregate measured by EPMA with a spatial resolution of 100 mm, it is possible to discriminate paste part in concrete. Because Cl penetrates into concrete through paste part, Cl concentration profile obtained by EPMA is effective for the estimation of apparent Cl diffusion coefficient, Da. The absolute Cl concentrations by EPMA are confirmed by comparing with traditional slicing and grinding methods. Based on the measurement results, Da of various concrete mixtures are calculated and the estimation is shown equivalent with conventional methods. Estimation of Chloride Diffusion Coefficient of Concrete Using Mineral Admixtures Tatsuhiko Saeki, Kenji Sasaki and Kenta Shinada Journal of Advanced Concrete Technology, 4(3) 385-394, 2006 It is well known that mineral admixtures, such as granulated blast-furnace slag and fly ash, control the ingress of chloride ions into concrete. However, the effects of the qualities and the replacement ratios of these admixtures on the diffusivity of chloride ions are not clear. Moreove r, the micro-structure of concrete is changed due to carbonation and change in micro-structure affects mass transfer in concrete. This effect on chloride diffusivity of concrete using mineral admixtures has not been clarified sufficiently. Therefore, in this study, the chloride ion diffusion coefficients of mortar specimens containing mineral admixtures were measured, and the influences of the kinds of mineral admixtures, replacement ratios and carbonation on chloride diffusion coefficient were estimated. The relation between micro-structure and diffusion coefficient was studied. Furthermore, the prediction method of the diffusion coefficient was proposed by the use of the amounts and properties of hydration products as parameters. Modeling of Calcium Leaching from Cement Hydrates Coupled with Micro-Pore Formation Kenichiro Nakarai, Tetsuya Ishida and Koichi Maekawa Journal of Advanced Concrete Technology, 4(3) 395-407, 2006 A computational system for predicting the long-term degradation of cement hydrates due to calcium leaching is presented. The leaching of calcium ions from hardened cement hydrates is simulated as the multi-phase equilibrium of calcium in solid and liquid phases and their transport is formulated on the basis of thermodynamics. The time-dependent properties of cement hydrates associated with hydration, pore-structure development, and moisture transport are evaluated by integrating calcium leaching and statistical models of chemo-physics. The proposed model delivers reasonable predictions of calcium leaching in high-performance concrete with a low water-to-cement ratio as self-curing takes place. Influence of Surface Energy on Compressive Strength of Concrete under Static and Dynamic Loading Hiromichi Matsushita and Kouzou Onoue Journal of Advanced Concrete Technology, 4(3) 409-421, 2006 To clarify the compressive static and fatigue strength of concrete immersed in various liquids, experimental studies were conducted. The influence of the surface tension of immersion liquid on static and fatigue strength of concrete were examined based on the knowledge that (1) the fracture process of concrete at the macro scale is the result of generation and propagation of internal microcracks, (2) strain energy is partially released as surface energy when microcracks are formed, and (3) the magnitude of the surface energy between a solid and a liquid is affected by the surface tension of the liquid. The results indicate that the larger the surface tension of the immersion liquid, the smaller the static and fatigue strength of concrete, and that these are characterized by a linear relationship. It also became clear that the fatigue of concrete in air hardly matters whereas special attention should be given to the fatigue of concrete in the case of concrete structures that are frequently immersed in liquid with a larger surface tension than water, such as marine structures. Influence of Shrinkage-Reducing Admixtures on Early-Age Properties of Cement Pastes Dale P. Bentz Journal of Advanced Concrete Technology, 4(3) 423-429, 2006 Because most shrinkage-reducing admixtures (SRAs) significantly reduce the surface tension of a cement paste pore solution, they will naturally influence all physical properties and processes that are dependent in some way on surface tension. Such properties include internal relative humidity, capillary stresses, and freezing point depression, all via the Kelvin equation and its variants (Kelvin-Laplace, Gibbs-Thomson). Processes that will thus be strongly influenced by the presence of SRAs include drying, autogenous stress and strain development, and freezing. In this paper, experimental measurements of these processes in cement pastes and mortars with and without SRA additions will be presented in light of the Kelvin equation. The experimental measurements that are applied to early-age specimens include x-ray absorption measurements to quantify drying profiles, bulk mass loss measurements, measurements of internal relative humidity, assessments of autogenous deformation under sealed curing conditions, and low temperature calorimetry scans to quantify freezable water content. The results indicate that SRAs can provide benefits in several new applications beyond their conventional usage to reduce drying shrinkage. Concrete or FRP Jacketing of Columns with Lap Splices for Seismic Rehabilitation Stathis Bousias, Alexis-Loukas Spathis and Michael N. Fardis Journal of Advanced Concrete Technology, 4(3) 431-444, 2006 Seismic rehabilitation of rectangular columns having corner deformed bars lap-spliced at floor levels through RC-jacketing or CFRP-wrapping, is experimentally studied. In three unretrofitted columns deformation capacity and energy dissipation drops fast with lap length below 45 bar-diameters. Three columns are cyclically tested after concrete jacketing of their full length and another nine after CFRP-wrapping of the lap splice and plastic hinge region. Five CFRP layers are more effective than two, but the improvement is not major. The positive effect of FRP-wrapping on flexural resistance, ultimate deformation and energy dissipation decreases, when lap length is reduced. There is a limit to the improvement due to FRP-wrapping: if lapping is as short as 15 bar-diameters, its adverse effects on force capacity and energy dissipation cannot be sufficiently removed by FRP-wrapping. Overall, RC-jacketing is more effective than FRP-wrapping for the improvement of the deformation capacity of columns with 15 bar-diameter lapping. Three-Dimensional Fatigue Simulation of RC Slabs under Traveling Wheel-Type Loads Koichi Maekawa, Esayas Gebreyouhannes, Tetsuya Mishima and Xuehui An Journal of Advanced Concrete Technology, 4(3) 445-457, 2006 A direct path-integral scheme with fatigue constitutive models for concrete tension, compression and rough crack shear is used to predict the life-cycle of RC slabs. The three-dimensional fatigue analysis successfully predicts the characteristic mode of failure under moving loads as well as in the case of fixed-point pulsation in shear. Importantly, drastically shortened fatigue life under traveling wheel-type loads is mechanically demonstrated by implementing a constitutive model of cracked concrete using a direct path-integral method of fatigue damage simulation. A sensitivity study is carried out to clarify the influence of shear transfer decay and compression fatigue on RC slab performance. The effect of boundary conditions on fatigue life is also investigated. Technical Report Flexural Behaviour of Reinforced Lightweight Concrete Beams Made with Oil Palm Shell (OPS) Delsye C. L . Teo, Md. Abdul Mannan and John V. Kurian Journal of Advanced Concrete Technology, 4(3) 459-468, 2006 This paper presents an investigation on the flexural behaviour of reinforced concrete beams produced from oil palm shell (OPS) aggregates. Utilising OPS in concrete production not only solves the problem of disposing this solid waste but also helps conserve natural resources. A total of 6 under-reinforced beams with varying reinforcement ratios (0.52% to 3.90%) were fabricated and tested. Data presented include the deflection characteristics, cracking behaviour, ductility indices and end-rotations. The investigation revealed that the flexural behaviour of reinforced OPS concrete beams was comparable to that of other lightweight concretes and the experimental results compare reasonably well with the current Codes of Practice. It was observed that beams with low reinforcement ratios satisfied all the serviceability requirements as per BS 8110. [PDF:354k]