Volume 8, No. 3 On Durability of SHCC Gideon P.A.G.van Zijl and Folker H. Wittmann Journal of Advanced Concrete Technology, 8(3) 261-271, 2010 Strain-hardening cement-based composites (SHCC) resist increased tensile stress after first crack formation, over a significant range of tensile strain. This increased strength and strain capacity is achieved by effective crack bridging by fibres, across multiple cracks of widths in the micro-range. Whether the crack width limitation translates into increased durability through retardation of ingress of moisture, gas and other deleterious matter, is scrutinised in this paper. This is done by evaluation of recent test results from several laboratories internationally. The question whether these small crack widths are maintained under sustained, cyclic or other load paths is also addressed, concluding that the crack widths are not independent of the loading path. This contribution summarises the State-of-the-Art report prepared in the period 2005 to 2009 by RILEM TC 208-HFC, Subcommittee 2: Durability of SHCC. The potential of the comparatively new composite material becomes obvious, yet it is clearly outlined that further research is necessary before we fully understand the basic mechanisms underlying durability of SHCC. The JSCE Recommendation for design of SHCC (HPFRCC) structural elements is a useful tool but it should be complemented by a recommendation on service life design in the future. Carbonation of γ-Ca2SiO4 and the Mechanism of Vaterite Formation Tsuyoshi Saito, Etsuo Sakai, Minoru Morioka and Nobuaki Otsuki Journal of Advanced Concrete Technology, 8(3) 273-280, 2010 The carbonation of γ-Ca2SiO4 ( γ-C2S) and mechanism of vaterite formation have been investigated by evaluating the crystal structure of both γ-C2S and vaterite. The samples used were autoclaved calcium silicate hydrate hardening bodies prepared from Ordinary Portland Cement (OPC), γ-C2S and α-quartz and then subjected to accelerated carbonation. The ratio of OPC to γ-C2S was varied. Ca²+ in both γ-C2S and vaterite was found to be coordinated to six O²-. In addition, both γ-C2S and vaterite have similar atomic arrangement of O²- and Ca²+ and Ca-O bond distance. Therefore, it is proposed that vaterite mainly formes from γ-C2S via topotactic reaction during accelerated carbonation. Influence of Patch Repair Material on Electrochemical Desalination of Concrete Hiroshi Minagawa and Makoto Hisada Journal of Advanced Concrete Technology, 8(3) 281-290, 2010 This study experimentally examined the influence of patch repair materials on the electrochemical desalination method for reinforced concrete. The experimental parameters are the electric resistivity and the repair area ratio of patch repair materials. The evaluation items were the amount of desalination and the current density distribution at the surface of rebar. In addition, an assessment method to estimate the amount of desalination by using core samples obtained from an existing member was proposed. As a result of the experiment, the current density at the surface of rebar increased near the boundary between the patch repair material and the concrete, also the distribution depended on the electrical resistivity and the repair area ratio of patch repair materials. Moreover, the amount of the desalination increased as the electric resistivity of patch repair materials increased. Optimum Surface Protection System with Silane Type Water Repellents Akira Hosoda, Yashinori Matsuda and Kaoru Kobayashi Journal of Advanced Concrete Technology, 8(3) 291-302, 2010 To establish an optimum surface protection system with silane type water repellents, experimental investigations were conducted for 2 kinds of water repellents which had shown good water absorption controlling effect in the exposure test in an actual structure by the authors. For concretes with 4 kinds of mix proportions (35%, 42%, 50%, 65%), the effects of the age of the application of water repellents and the effects of the curing conditions before and after the application on penetration depth and on water absorption controlling effect were investigated. Furthermore, the specimens used for water absorption tests were subjected to weathering test to examine the durability of water absorption controlling effect. In dry concrete, both water repellents showed good water absorption controlling effect. We should apply the water repellents in earlier age to obtain better water absorption controlling effect, however, we proposed that water repellents should be applied not in too early age for low W/C concrete. The authors think that penetration depth of at least 1-2mm should be secured. Penetration depth and water absorption controlling effect was affected by curing conditions before and after the application. When the specimens with water repellents were subjected to the weathering test with Xenon arc lamp for 98days (equivalent to 2.8 years in Tokyo), no degradation of water repellent layer was observed. Considering the experimental results in this study, an optimum surface protection system for newly constructed structures was proposed. Effect of Detailing of Web Reinforcement on the Behavior of Bottle-Shaped Struts. Dipak Kumar Sahoo, Murali Sagar Varma Sagi, Bhupinder Singh and Pradeep Bhargava Journal of Advanced Concrete Technology, 8(3) 303-314, 2010 The effect of detailing of web reinforcement as per current design codes on the strength and serviceability behavior of bottle-shaped struts has been experimentally investigated, particularly in the context of codal minimum reinforcement requirements, by testing eleven scaled deep beams. The experimentally obtained efficiency factors of the bottle-shaped struts besides being significantly higher than the values given in the ACI 318-08 were also found to be sensitive to the amount of web reinforcement. The minimum web reinforcement requirements specified in current design codes were found to be adequate for controlling service load crack widths and the unreinforced bottle-shaped struts allowed in the ACI code were observed to violate the maximum crack width requirements. It has been shown that the transformation equation in the ACI code does not accurately represent the relationship between the strut efficiency factor and the amount of transverse reinforcement whereas the corrected version of the equation shows a clear dependence of the former on the latter. Smeared-Crack Modeling of R/ECC Membranes Incorporating an Explicit Shear Transfer Model Benny Suryanto, Kohei Nagai and Koichi Maekawa Journal of Advanced Concrete Technology, 8(3) 315-326, 2010 This paper presents the verification of analytical modeling for reinforced Engineered Cementitious Composite (R/ECC) in the context of a smeared, fixed crack approach. Verification is provided through analyses of six R/ECC panels subjected to pure shear. The analysis results demonstrate that the proposed models are capable of replicating various responses of the panels well, provided that tensile property of the ECC is calibrated against those obtained from the panel tests. This includes load-deformation responses, the magnitudes and directions of principal stress and principal strain, and failure modes. The results also demonstrate the possibility of representing the average interface shear transfer in the ECC with an explicit smeared model. Finally, this paper includes predictions of shear capacity of R/ECC panels with a wide range of reinforcement ratios and discussions regarding factors influencing shear strength. New Renovation Method for Jetty Structure Using High Durability Concrete Form Cured with CO2 Gas Kenzo Watanabe, Kosuke Yokozeki and Noboru Sakata Journal of Advanced Concrete Technology, 8(3) 327-336, 2010 Studies on reduction of life cycle cost and rationalized construction methods were carried out with emphasis on renovation of slab of jetty structure. Results of comparison of various kinds of renovation methods with the focus on slab of jetty structure in service revealed that a construction method using pre-cast concrete form with exceptionally enhanced durability was ideal. Analytical and experimental studies were carried out on durability design related to renovation methods, and test construction using new renovation method was implemented. Durability was verified after studies over the years, and a rational renovation method was proposed. Fluorescence Characteristic Analysis for Discriminating Fibers in Cementitious Composites Bang Yeong Lee, Taemin Kim and Yun Yon Kim Journal of Advanced Concrete Technology, 8(3) 337-344, 2010 This paper investigated the fluorescence properties of Polyvinyl Alcohol (PVA) fibers, Polyethylene Terephthalate (PET) fibers, Polyethylene (PE) fibers, and a matrix by using a spectrofluorometer. Optimal excitation and emission filters were also proposed to discriminate each synthetic fiber in the hybrid Strain Hardening Cementitious Composite (SHCC) by a multispectral fluorescence-imaging model and a Linear Discriminant Analysis (LDA). The experimental test results showed that the PVA fiber, PET fiber, and PE fiber used in the hybrid SHCC had a unique fluorescence characteristic with a peak. On the other hand, the matrix hardly showed any fluorescence intensity. The optimal excitation and emission filters of a multispectral imaging system for fiber detecting the hybrid SHCC are presented here as continuous forms. The selective optimum excitation and emission wavelengths that showed maximum relative transmission are 360-389 nm, 400-445 nm, 360-390 nm, and 360-389 nm for the PVA-PET, PVA-PE, PET-PE, and PVA-PET-PE fiber reinforced cementitious composites, respectively.