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 deterioration of SHCC. The JSCE Recommendation for design and construction of high performance fibre-reinforced composites with multiple fine cracks (HPFRCC) is a useful tool but it should be complemented by a similar recommendation on service life design in the future.
The carbonation of γ-Ca2SiO4 (γ-C2S) and mechanism of vaterite formation have been investigated by evaluating the crystal structures 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 arrangements of O2- and Ca2+ and Ca-O bond distances. Therefore, it is proposed that vaterite mainly forms from γ-C2S via a topotactic reaction during accelerated carbonation.
This study experimentally examined the influence of patch repair materials on the electrochemical desalination method for reinforced concrete. The experimental parameters are the electrical resistivity and the repair area ratio of the patch repair materials. The evaluation items were the amount of desalination and the current density distribution at the surface of the rebar. In addition, an assessment method to estimate the amount of desalination by using core samples obtained from an existing member was proposed. Experiment results showed that the current density at the surface of a rebar increased near the boundary between the patch repair material and the concrete, and that the distribution of current density depended on the electrical resistivity and the repair area ratio of the patch repair materials. Moreover, the amount of desalination increased as the electrical resistivity of patch repair materials increased.
To establish an optimum surface protection system with silane type water repellents, experimental investigations were conducted for 2 kinds of water repellents that had shown good water absorption controlling effect in a previous exposure test in an actual structure carried out by the authors. The effects of the age of application of water repellents and the effects of the curing conditions before and after the application on the penetration depth of water repellents and the water absorption controlling effect were investigated for concretes of different mix proportions with four different W/C, of 35%, 42%, 50%, 65%. Furthermore, the specimens used for the water absorption tests were subjected to a weathering test to examine the durability of the water absorption controlling effect. In dry concrete, both water repellents showed a good water absorption controlling effect. While it is generally considered desirable that the water repellents be applied at an early age to obtain a better water absorption controlling effect, the authors propose that water repellents should be applied not too early for low W/C concrete, in order to ensure a penetration depth of at least 1 to 2 mm. The penetration depth and water absorption controlling effect are affected by the curing conditions before and after application of the water repellents. When the specimens with water repellents were subjected to a weathering test using a Xenon arc lamp for 98 days (equivalent to 2.8 years of weathering in Tokyo), no degradation of the water repellent layer was observed. Considering the experimental results in this study, an optimum surface protection system for newly constructed structures is proposed.
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 though 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 a corrected version of the equation shows a clear dependence of the former on the latter.
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 the analysis of six R/ECC panels subjected to pure shear. The 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. These responses include 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 crack-shear transfer in the ECC with an explicit smeared model. Finally, this paper includes predictions of the shear capacity of R/ECC panels with a wide range of reinforcement ratios and concludes with discussions regarding factors influencing shear strength.
Studies on reduction of life cycle cost and rationalized construction methods were carried out with emphasis on the renovation of slabs of jetty structures. The results of a comparison of various kinds of renovation methods with focus on slabs of jetty structures 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 a new renovation method was implemented. Durability was verified after the studies over the years, and a rational renovation method was proposed.
This paper investigated the fluorescence properties of Polyvinyl Alcohol (PVA) fibers, Polyethylene Terephthalate (PET) fibers, Polyethylene (PE) fibers, and a cement-based matrix by using a spectrofluorometer. Optimal excitation and emission filters were also proposed to discriminate each synthetic fiber in the hybrid Engineered Cementitious Composite (ECC) 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 ECC had a unique fluorescence characteristic with a peak. On the other hand, the cement-based matrix showed a little fluorescence intensity. The optimal excitation and emission filters of a multispectral imaging system for detecting fibers in the hybrid ECC 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.
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