Volume 7, No. 1 Effectiveness of Polycarboxylate Superplasticizers in Ultra-High Strength Concrete: The Importance of PCE Compatibility with Silica Fume Johann Plank, Christof Schroefl, Mirko Gruber, Matthias Lesti and Roland Sieber Journal of Advanced Concrete Technology, 7(1) 5-12, 2009 Methacrylate ester as well as allylether based polycarboxylates (PCEs) were synthesized to plasticize pastes of cement and silica fume having a water/cement ratio of 0.22. Methacrylate ester copolymers were found to disperse cement well, whereas allylether copolymers are more effective with silica fume. Mechanistic investigations revealed that in cement pore solution, the surface charge of silica fume becomes positive by adsorption of Ca2+ onto negatively charged silanolate groups present on the silica surface. This way, polycarboxylate copolymers adsorb to and disperse silica fume grains. Thus, mixtures of both copolymers were tested in cement-silica fume pastes. These blends provide significantly better dispersion than using only one polymer. Apparently, the surfaces of hydrating cement (here mainly ettringite) and silica fume are quite different with respect to their chemical composition. Therefore, PCEs with different molecular architectures are required to provide maximum coordination with calcium atoms present on these surfaces. Relation between the shape of silica fume and the fluidity of cement paste at low water to powder ratios Etsuo Sakai, Yasuo Kakinuma, Kenji Sakamoto and Masaki Daimon Journal of Advanced Concrete Technology, 7(1) 13-20, 2009 The effect of the properties of silica fume on the fluidity of ultra high strength cement paste (UHCP) using a polycarboxylate based superplasticizer, silica fume, and low heat Portland cement was investigated. As the quantity of superplasticizer was increased, the flow curve of UHCP changed from Bingham flow to pseudo-plastic flow to Newtonian flow. Also, the effect of silica fume on the fluidity of UHCP was large, in particular the effect on the shape of powder particles smaller than 0.3 mm was large. It is suggested that this is due to the agglomeration structure, the packing state, and the ball bearing effect of the paste due to the shape of the silica fume. Mechanical Properties and Durability of Normal and Water Reduced High Strength Grade 60 Concrete Containing Rice Husk Ash Hilmi Bin Mahmud, Muhammad Fakhar Abdul Malik, Rahaimi Abdul Kahar, Muhammad Fauzi Mohd Zain and Sudharshan Naidu Raman Journal of Advanced Concrete Technology, 7(1) 21-30, 2009 This paper reports an investigation on the strength properties, a time dependent property as well as durability characteristics of normal and water reduced high strength concrete (WRHSC), with or without rice husk ash (RHA), designed to produce Grade 60 at 28 days. RHA was ﾔaddedﾕ or ﾔreplacedﾕ at/by 5% - 20% of the cement content. A PCE superplasticizer was added to all mixes to provide workability in the range of 150 ﾐ 200 mm slump. Based on the initial trial mixes, four high strength concrete mixes were selected for further tests on mechanical properties, drying shrinkage and durability. Incorporation of RHA increases the strength of concrete, reduces the drying shrinkage and improves the durability of concrete, when compared to conventional OPC concrete. Macro-cell Corrosion in Reinforcement of Concrete under Non-homogeneous Chloride Environment Ominda Nanayakkara and Yoshitaka Kato Journal of Advanced Concrete Technology, 7(1) 31-40, 2009 This research study was carried out to identify the behavior of macro-cell corrosion when the concrete specimens are subject to the effect of homogeneous and non-homogeneous chloride environments. Periodic macro-cell corrosion currents were measured using a divided ferrous steel bar. Results show that macro-cell corrosion can be observed even when the surrounding chloride environment is homogenous. When the chloride environment is non-homogeneous, a higher macro-cell corrosion activity was observed in the vicinity of different chloride contents. Macro-cell corrosion activity becomes more rapid when the chloride content difference is increased. It was also observed that the macro-cell anodic and cathodic reactions periodically change their status from anodic to cathodic or cathodic to anodic. It is proposed that the time dependent variation of macro-cell corrosion is occurred due to the variation of oxygen and moisture concentrations by ongoing corrosion process which is briefly explained in this paper. Temperature Dependency of Chloride Induced Corrosion in Concrete Nobuaki Otsuki, Marish S. Madlangbayan, Takahiro Nishida, Tsuyoshi Saito and Melito A. Baccay Journal of Advanced Concrete Technology, 7(1) 41-50, 2009 Maintenance of reinforced concrete is a major concern around the world. In particular, special attention is now given to chloride induced corrosion which is considered as one of the most serious causes of concrete deterioration. Since corrosion is an electrochemical process, the influence of temperature on the deterioration of reinforced concrete should be considered. From these backgrounds, the objective of this study is to investigate the influence of temperature on the deterioration process of chloride induced corrosion in reinforced concrete. The results show that the rates of diffusion of substances and corrosion of steel bars rise with the increase in temperature and these phenomena was explained by Arrhenius theory using the concept of activation energy. Use of Slurry Infiltrated Fiber Concrete in RC Corner Connections Subjected To Opening Moments Mohammed A. Elnono, Hamed M. Salem, Ahmed M. Farahat and Ashraf H. Elzanaty Journal of Advanced Concrete Technology, 7(1) 51-59, 2009 The use of Slurry Infiltrated Fiber Concrete (SIFCON) in reinforced concrete corner connections subjected to opening bending moments has been experimentally investigated. An experimental program has been carried out, in which fifteen specimens have been tested; six reinforced concrete joints, one fiber reinforced concrete joint, and eight SIFCON joints. Different reinforcing barsﾕ details and different volume of fraction of fibers (Vf) have been investigated. It was found that, in all the RC specimens, the joints failed before reaching the capacity of the connecting members. There was also a significant difference in the different jointsﾕ efficiency due to the variety of the reinforcement details. The use of SIFCON in the joints increased both the joints capacity and ductility. The enhancement of the joint capacity and ductility could reach as high as 66% and 173%, respectively. This is attributed to the ability of the high volume of fibers to effectively bridge the cracks and retard the compression failure of the diagonal struts in the joints. The increase in the amount of fibers was proven to directly enhance the behavior of the SIFCON joints. In joints with Vf=6% and 8%, the joint capacity exceeded the connecting membersﾕ capacity leading to failure in the members before the joints, which is an advantageous requirement of the design. Tension stiffening model for numerical analysis of RC structures by using bond-slip relationship Sam-Young Noh Journal of Advanced Concrete Technology, 7(1) 61-78, 2009 In this paper a tension stiffening model based on the bond-slip relationship is introduced and adopted in a finite multi-layered shell element formulation for surface structure analysis. The tension stiffening effect evaluated at the meso-level is taken into account in the constitutive law of reinforcement for the macro-level by defining a crack element at the Gauss point. The crack element is iteratively analyzed by means of a step-by-step integration, which allows application of any complicated bond laws. To define the crack element, a crack spacing model considers the crack formation grade. As a relevant factor in this tension stiffening concept, the reinforcement cracking stress may be evaluated by taking the fractile value of the concrete tensile strength. Through several simulations, the validity of the concept is systematically investigated under monotonic and cyclic loading. The analysis under cyclic loading shows the effect of the re-contact of the crack flanks. The numerical examples demonstrate the applicability of the applied reinforced concrete model with a tension stiffening effect.. Experimental Investigation on Shear Cracking Behavior in Reinforced Concrete Beams with Shear Reinforcement Mohamed Zakaria, Tamon Ueda, Zhimin Wu and Liang Meng Journal of Advanced Concrete Technology, 7(1) 79-96, 2009 This paper presents an experimental investigation to clarify shear cracking behavior of reinforced concrete beams. The effects of the various influential parameters on the spacing between shear cracks and the relationship between shear crack width and stirrup strain at the intersection with shear cracks were carefully investigated. It was found that shear crack width proportionally increases with both the strain of shear reinforcement and with the spacing between shear cracks. Greater diagonal crack spacings were found in larger beams and hence resulted in wider shear crack width. The test results also revealed that shear reinforcement characteristics (side concrete cover to stirrup, stirrup spacing and/or stirrup configuration) and longitudinal reinforcement ratio play a critical role in controlling the diagonal crack spacings and openings. It was illustrated that the distance of shear crack from the crack tip and the intersection with the nearest reinforcement can significantly affect the variation of shear crack width along the same shear crack. Conversely, the loading paths (loading, unloading and reloading paths) show an insignificant effect on shear crack width-stirrup strain relationship. Finally, the experimental results presented are useful information for the development of a rational shear crack displacement prediction method in existing design codes. Composite Strut and Tie Model for Reinforced Concrete Deep Beam Kil-Hee Kim, Woo-Bum Kim, Jin-Man Kim and Sang-Woo Kim Journal of Advanced Concrete Technology, 7(1) 97-109, 2009 Monotonic shear loading tests were conducted on three half-scaled reinforced concrete deep beams with shear span to depth ratios of 0.5 to 0.75. Obtained test result was investigated in detail based on the experimental measurements and the finite element analysis. From these investigations a new macro-model for deep beam was established. This model is composed of two crooked main struts formed between both beam end sections and branched-off sub struts. Compression force induced to main strut balances to the flexural compression and the external shear force. Bond stress of longitudinal reinforcement and tension force of stirrup produces the diagonal compression in the sub strut. Theoretically predicted shear strengths of tested deep beams showed good agreement with experimentally observed shear strengths, where the effective strength of concrete was assumed to be 75 % of cylinder strength. Behavior of Beams Strengthened with Steel Fiber RC Overlays Mohamed M. Ziara Journal of Advanced Concrete Technology, 7(1) 111-121, 2009 Strengthening of reinforced concrete beams using steel fiber reinforced concrete (SFRC) overlays has been investigated in the test program described in this paper. Two methods have been used to connect the overlays to the original beams, i.e. chemical and mechanical bonding. In the chemical bonding, 2-component epoxy resin bonding agent has been used. The mechanical bonding was achieved by welding the stirrups in the overlays to the stirrups in the original beams only near each support. In general, the weld bonded strengthened beams have achieved a better structural behavior in terms of load carrying capacity and failure mode compared to the epoxy bonded beams. The epoxy bonded beams have reached same load and ductility levels obtained from an identical monolithically cast control beam which was included in the test program for comparison purposes. However, at failure separation cracks have occurred at the common interface between the overlays and the original beams. On the other hand, the weld bonded strengthened beams have behaved in a flexural ductile manner and achieved higher load carrying capacity compared to the control beam. The inter-laminar shear failure did not occur in these beams which have acted as a single unit up to the failure. Use of High-Strength Bars for the Seismic Performance of High-Strength Concrete Columns Hassane Ousalem, Hiroto Takatsu, Yuji Ishikawa and Hideki Kimura Journal of Advanced Concrete Technology, 7(1) 123-134, 2009 To accommodate the vertical expansion of high-rise buildings and required large column-spacing, and assure a high structural performance to supporting elements, use of high-strength materials is sought as a solution. Accordingly, an experimental investigation of the effectiveness of veryhigh- strength steel bars in improving the performance of ultra-high-strength concrete columns is described. The concrete of 171 MPa strength contained steel fibers. Two grades of high-strength steel bars were used for longitudinal bars in columns. While the SD685-grade is already used in practice, the SD980-grade is still under development. The 1/4 scaled columns were subjected to high levels of compression and tension, and to cyclic lateral loads with an anti-symmetric double curvature bending. The tested columns proved to be ductile and showed good performances. The maximum recorded lateral strength values were at least 30% and 10% greater than those obtained by using ACI and AIJ equations, respectively. The advantage of using steel fibers was apparent by the limited and narrow cracks even at large lateral drifts. It is also suspected to have an impact on preventing buckling of the longitudinal reinforcement. The SD980-grade bars were found very effective in terms of tension axial strength, delay of crack evolution and shear strength degradation, and to be slightly less effective than the SD685 grade bars in terms of shear strength and energy dissipation. Fundamental Property of Chloride Inhibiting and Low Heat Cement for Marine Concrete Structures Cheolwoo Park, Jongsung Sim and Jongryul Lee Journal of Advanced Concrete Technology, 7(1) 135-142, 2009 As construction of marine concrete structure become more common, durability issues take more important considerations. This study introduces the newly developed chloride inhibiting and low heat cement, which is quaternary blended cement. The primary target application is massive scaled marine concrete structures. The adiabatic temperature rise of the developed cement was about 30% and 28% lower than the ordinary Portland and blast furnace slag cement, respectively. The resistance to chloride ion penetration was much higher compared to the blast furnace slag cement. Based on the guidelines from ASTM C1202 it was considered as very low at 28 days. It can be said that, therefore, the primary purposes of the developed cement was surely accomplished. In addition, the developed chloride inhibiting and low heat cement may satisfy the strength requirement of general purpose marine concrete applications without significant concerns on early age strength. The developed cement can provide sufficient resistance to freezing-thawing attack as long as proper air content is obtained.