Volume 4, No. 2 Special section:Structure and Performance of Chemical Admixture edited by Prof. E. Sakai New Trends in the Development of Chemical Admixtures in Japan (Invied Paper) Etsuo Sakai, Atsumi Ishida and Akira Ohta Journal of Advanced Concrete Technology, 4(2) 211-223, 2006 This paper describes the history and new trends in the development of chemical admixtures in Japan. PC (polycarboxylic acid)-based agents are the main products in the superplasticizer market. A low-stickiness type PC-based superplasticizer has been developed based on the conventional PC-based superplasticizer. The flowing speed of concrete with low stickiness type PC-based superplasticizer is faster than that with the conventional PC-based superplasticizer. By addition of a new viscosity agent consisting of a mix of anionic and cationic surface active agents, the three dimensional reticulation structures is formed in fresh cement paste and the viscosity of the cement paste can be increased and segregation can be prevented. The hydration of cement in sludge water is controlled by addition of a set-retarder, and the specific surface area of cement does not increase while a large amount of unreacted alite remains in the sludge water. Recycling of concrete at ready mixed concrete plants is possible without adversely influencing the properties of concrete when sludge water with the set-retarder containing gluconate salt is used. The slurry type and powder type calcium aluminate based accelerator (CA) and calciumsulfoaluminate based accelerator (CSA) for shotcrete have been developed. In the case of CA, the final setting time of the mortar is accelerated by increasing the dosage. By adding of CSA, both the initial and final setting times of mortar are shortened with increased dosages. Effect of Chemical Structure on Steric Stabilization of Polycarboxylate-based Superplasticizer Toyoharu Nawa Journal of Advanced Concrete Technology, 4(2) 225-232, 2006 The effects of chemical structures of graft copolymer on cement-dispersing performance were investigated in order to elucidate the fluidizing mechanism of polycarboxylate-based superplasticizer containing graft copolymer with polyethylene oxide graft chains. Graft copolymer with longer graft chains showed better dispersing stability at small amount of adsorption. The adsorption study indicated that the graft chains were stretched as increasing the adsorption density. Thus the thickness of graft chain in copolymer adsorbed on cement particle depends on the average distance between two graft copolymers and the graft chain spacing within copolymers. depending on the geometric feature of copolymer. The modified steric stabilization model incorporating the extension of graft chains due to adsorption can well explain the relationship between the adsorption and the flow of paste containing different graft copolymers. Impact of Molecular Structure on Zeta Potential and Adsorbed Conformation of α-allyl-ω-methoxypolyethylene Glycol - Maleic Anhydride Superplasticizers Johann Plank and Bernhard Sachsenhauser Journal of Advanced Concrete Technology, 4(2) 233-239, 2006 α-Allyl-ω-methoxypolyethylene glycol - maleic anhydride copolymers were synthesized with side chain lengths nEO from 0-130 and characterized by aqueous GPC. A representation of their molecular conformation (e.g. worm-, brush- or star-like polymers) was developed. The amount of polymer adsorbed on cement rapidly decreases with increasing side chain length nEO. Zeta potential measurements using the electroacoustic method in cement paste with w/c = 0.5 indicate that worm-like copolymers with nEO < 7 adsorb flat (ﾒtrainﾓ type) and form a densely packed, thin polymer film. In this case, the adsorbed amount of copolymer is high. For star polymers with nEO > 34, preferred orientation of the polymer main chain is perpendicular to the cement surface (ﾒtailﾓ type). The result is a thick polymer layer, with a second electrochemical double layer on top. For star polymers, the adsorbed amount is low because of the higher surface occupancy of horizontally layered side groups. Fuidity Performances Evaluation of Cement and Superplasticizers Kazuo Yamada, Takumi Sugamata and Hiroshi Nakanishi Journal of Advanced Concrete Technology, 4(2) 241-249, 2006 For durable concrete structures, the first important step is the sound placing of concrete. In order to control the workability of concrete for sound placing, compatibility problems among concrete materials have been a great issue in this decades. Every engineer wants to have some methods to examine the fluidity performance of cement and superplasticizers. In this study, the way to examine the fluidity performance is discussed from the viewpoint of fundamental mechanisms. One important point is the deforming properties of superplasticized concrete. When fresh concrete deform homogeneously, the workability of concrete can be explained by one basic theory of superplasticizer, i.e. proportional correlation of the adsorption amount of superplasticizer per surface area of hydrate to the fluidity. Moreover, the examination of the fluidity performance of cement and superplasticizers should consider the condition of real concrete in the respect of water-to-cement ratio and mixing procedure of materials. Relationships between Rheological Constant of Cement Paste and Fluidity of High-Fluidity Concrete Eiji Maruya, Masashi Osaki and Hideaki Igarashi Journal of Advanced Concrete Technology, 4(2) 251-257, 2006 In order to develop a method for evaluating fluidity of high-fluidity concrete using cement paste, relationships between rheological properties of cement paste and slump flow of the concrete were investigated. Several commercial Portland cements were used. Rheological constants of the cement paste were measured with a rotating viscometer changing the mixing procedure, dosage of a superplasticizer, and the operation conditions of the viscometer. It was found that yield values of cement pastes measured with a parallel-plate type rotating viscometer showed good correlation with slump flows of concretes. Analytical Hydration Model for Filler Rich Self-Compacting Concrete Anne-Mieke Poppe and Geert De Schutter Journal of Advanced Concrete Technology, 4(2) 259-266, 2006 For the realisation of self-compacting concrete, high filler contents are generally added to the cementitious system. In order to avoid problems with excessive heat of hydration during hardening, inert filler materials can be used. Within this research two different filler types are considered: limestone and quartzite filler, and this in combination with different types of Portland cement. Although the mentioned filler material is considered to be inert with respect to cement hydration, experimental research shows that it is interfering with the hydration processes. On the one hand the reaction speed is influenced due to a modified nucleation possibility. On the other hand, the reaction mechanism is also altered due to the presence of the large filler content, with a new hydration peak occuring, especially in the case of limestone filler. Based on isothermal conduction calorimetry on different cement filler systems, an existing hydration model for blended cement is modified for the situation of cement filler systems. Within the degree of hydration based hydration model for the filler rich cementitious systems, the cement powder ratio is an important parameter. The analytical model results in an accurate prediction of the heat of hydration during the hardening process. This was also verified by means of adiabatic hydration tests on concrete. Development of Self-Healing System for Concrete with Selective Heating around Crack Tomoya Nishiwaki, Hirozo Mihashi, Byung-Koog Jang and Kazuaki Miura Journal of Advanced Concrete Technology, 4(2) 267-275, 2006 A fundamental study is carried out to develop a kind of smart concrete that has the self-healing system with heating devices. Self-diagnosis composite is employed as the heating device that can heat up the cracked part of concrete. This heating device and a pipe made with heat-plasticity organic film containing repair agent are embedded in concrete. The film is melted by proper heat. Selective heat around a crack can melt the film to let the repair agent fill up the crack and harden the repair agent in the crack. Three-dimensional thermal analysis and an experimental study is carried out to confirm the proposed method. Tensile Creep of High-Strength Concrete Hans-Wolf Reinhardt and Tassilo Rinder Journal of Advanced Concrete Technology, 4(2) 277-283, 2006 Tensile creep tests on high-strength concrete have been performed. Besides up-to-date creep data which have been generated a new phenomenon has been discovered, i. e. shrinkage of loaded specimens is larger than of non-loaded ones. It seems that this phenomenon is in agreement with Powersﾔ creep theory. Factors Affecting the Carbonation of Railway Rigid-Frame Viaducts Chikara Kawamura, Yukihiro Tanimura, Masamichi Sogabe, Koji Matsuhashi, Tsutomu Sato and Tamon Ueda Journal of Advanced Concrete Technology, 4(2)285-300, 2006 Recent years have seen the promotion of research into the carbonation of concrete. The standard specifications for concrete structures, outlined by the Japan Society of Civil Engineers (JSCE), prescribe a method to verify the durability concerning carbonation. However, as the carbonation rate is largely governed by environmental conditions, it is important to quantitatively assess the effect of these conditions on the carbonation of concrete structures by applying the method to actual structures. To this end, we investigated the factors affecting the progress of carbonation in different members, based on the results of a survey on a rigid-frame railway viaduct that had been in service since its construction several decades before. The study results indicate that the carbonation rate of columns varies with height, and depends on the effects of exposure to rainwater. In contrast, there are comparatively small differences in the carbonation rate at different points on beams or slabs. Time-Dependent Constitutive Model of Solidifying Concrete Based on Thermodynamic State of Moisture in Fine Pores Shingo Asamoto, Tetsuya Ishida and Koichi Maekawa Journal of Advanced Concrete Technology, 4(2) 301-323, 2006 An enhanced multi-chemo-physical model for the time-dependent deformation of concrete is proposed based on thermodynamic state of moisture in micro-pores. The moisture migration mechanism is divided into 1) moisture transport through CSH gel grains and 2) water in motion within the inter-particle spaces of hydrate micro-products. The new kinematic model makes it possible to simulate both long- and short-term concrete creep. An enhanced mechanistic law of stress path dependency is introduced to cope with a wide variety of stress and ambient histories as well. Time-dependency at elevated temperature is also investigated with current high-accuracy thermo-hygro dynamics. The instantaneous plasticity in direct connection with evaporating moisturefrom CSH crystal inter-layers is incorporated into the predictive system. Although some mechanisms remain unverified, drying shrinkage and creep at high temperature are fairly simulated. Computer-Aided Analysis of Reinforced Concrete Using a Refined Nonlinear Strut and Tie Model Approach Hamed M. Salem and Koichi Maekawa Journal of Advanced Concrete Technology, 4(2) 325-336, 2006 This paper presents a computer program for implementing a refined nonlinear strut-tie model approach for the practical design and analysis of disturbed regions in structural concrete. Nonlinear techniques in the selection, analysis and verification processes of a strut and tie model are incorporated in this program to eliminate the limitations of the conventional strut and tie model relating to the behavior and strength predictions of reinforced concrete. For the verification of the proposed model, the model results are compared to the experimental results of one-quarter scale simply supported bottom-loaded deep beams. Analytical results showed a lower bound solution that agreed well with the experimental results. It was concluded that the nonlinear strut and tie model provides more economical design than the conventional strut and tie model. It was also concluded that for higher strength concrete, the strength of struts and nodal zones given by the ACI-318 02 code is overestimated and needs refinement to account for the brittleness of high strength concrete.