Volume 6, No. 3 Concentration and Molecular Weight of Superplasticizer in Pore Water from Hardened Cement Pastes Hideki Fujita, Kazuko Haga, Masahito Shibata and Morihiro Mihara Journal of Advanced Concrete Technology, 6(3) 389-395, 2008 There are concerns about the possible increase in the solubility of radionuclides due to the presence of superplasticizers proposed to be added to cementitious materials in a radioactive waste repository. The concentration and molecular weight of a polycarboxylate type SP in hardened cement pastes has been investigated experimentally in this work. The measurement of total organic carbon in both the pore water extracted from hardened cement pastes by compression and the curing water was performed. A molecular weight of SP in pore water was analyzed to investigate the chemical form. It was found that most SP (more than 90%) remained in the solid phase. Organic substance of a low molecular weight was detected in the pore water by gel permeation chromatography, possibly due to selective absorption of a high molecular weight part of SP.. Quantifying the Effects of Hydration Enhancement and Dilution in Cement Pastes Containing Coarse Glass Powder Narayanan Neithalath Journal of Advanced Concrete Technology, 6(3) 397-408, 2008 Various non-standard filler materials are used in concretes to improve fresh and hardened concrete properties. This paper reports results from investigations on the property development of cement pastes incorporating a coarse glass powder as filler. The characteristics investigated are the degrees of hydration, relative strength development, and heat of hydration. Using a mixing model for non-evaporable water content, it is shown that the incorporation of glass powder results in enhancements in the degrees of hydration of the cement grains in the system. In order to quantify the relative effects of dilution (reduction in cement content, and thus of the hydration products) and increase in degree of cement hydration on the mechanical properties, a strength index is proposed in this paper. Using the strength index, it is shown that the use of coarse glass powder filler is beneficial in pastes with lower water-to-cement ratio (w/c), where a portion of cement remains unhydrated. Increasing glass powder contents are observed to result in increased heat of hydration per unit mass of cement. However, beyond a certain glass powder content, the heat of hydration decreases due to the dominance of the dilution effect. The ultimate heat of hydration obtained from a three parameter model, the cement content, and the ultimate degrees of hydration are used to specify a new parameter termed the total ultimate heat of hydration. It is suggested that the total ultimate heat of hydration per unit volume of paste can be used to compare between mixtures made with different w/c and glass powder contents since this term, as defined in this paper, accounts for both the hydration enhancement and dilution effect from filler addition. Dark Discoloration of Fair-face Concrete Surfaces-Transport and Crystallization in Hardening Concrete Doris Strehlein and Peter Schiessl Journal of Advanced Concrete Technology, 6(3) 409-418, 2008 Especially during outdoor concrete production in winter conditions light-dark discoloration frequently spoil the appearance of fair-face concrete surfaces. At the Centre for Building Materials (cbm) of the Technical University of Munich, the discoloration which occurs in practice is characterized in terms of surface structure, near-surface microstructure and mineralogical composition. By varying the conditions of concrete production and storage, it was possible to simulate the discoloration in the laboratory and thus determine the main factors responsible for the discoloration. By comparing the results of field and laboratory investigations, the transport and crystallisation processes which occur in hardening concrete were derived which lead to discoloration of fair-face concrete surfaces. Mechanisms of Corrosion-Induced Cracks in Concrete at Meso- and Macro-Scales Masayasu Ohtsu and Farid A. K. M. Uddin Journal of Advanced Concrete Technology, 6(3) 419-429, 2008 Following the initiation of corrosion in reinforcement, expansion of corrosion products generates corrosion-induced cracks in concrete. At the meso-scale, accumulation and coalescence of micro-cracks create the fracture process zone. Since nucleation of an individual micro-crack can be detected by acoustic emission (AE) techniques, the moment tensor analysis of AE waves is applied to quantitatively identify cracking kinematics of a location, a crack-type and a crack orientation. At the macro-scale, initiation and extension of the corrosion-induced cracks are analyzed by means of classical fracture mechanics, applying the boundary element method (BEM). The generation of corrosion-induced cracks was simulated in expansion tests on concrete specimens. Kinematical mechanisms of micro-cracks were identified by the SiGMA (Simplified Green's functions for Moment tensor Analysis) analysis. By applying the two-domain BEM analysis, extension of the corrosion-induced crack in an arbitrary direction was analyzed. With respect to the orientations of crack extension, results of the BEM analysis were compared with those of the SiGMA analysis, introducing the normalized stress intensity factors. It is demonstrated that extension of the corrosion-induced crack is governed by the mode-I failure both at the meso-scale and at the macro-scale. Experimental Behaviour of Carbon FRP Reinforced Concrete Beams at Ambient and Elevated Temperatures Muhammad Masood Rafi and Ali Nadjai Journal of Advanced Concrete Technology, 6(3) 431-441, 2008 The applications of fibre reinforced polymer (FRP) bars in buildings can provide a potential market for their use. Since buildings could be exposed to elevated temperatures the behaviour of carbon FRP (CFRP) reinforced concrete (RC) beams is studied at high temperatures and compared with normal temperature behaviour. Steel RC beams were used as control specimens. Failure modes of beams at normal and elevated temperatures were found to be the same. The stiffness of cracked FRP RC was less than steel reinforced concrete at normal temperature whereas FRP reinforced beams were stiffer than steel RC beams at elevated temperatures. Evaluation of Shear Crack Width in I-Shaped Prestressed Reinforced Concrete Beams Sudhira De Silva, Hiroshi Mutsuyoshi and Eakarat Witchukreangkrai Journal of Advanced Concrete Technology, 6(3) 443-458, 2008 Recently, Prestressed Reinforced Concrete (PRC) has been accepted as a reasonable structural member that permits cracking. A PRC member is a visible design alternative to either reinforced concrete (RC) or fully prestressed concrete (PC). In Japan, PRC has been widely used for bridge structures from the economical point of view. The PRC members are generally designed to allow cracking under full service loads. Flexural cracking in PRC beams has been already studied and flexural crack width can be accurately predicated by equations available in the present codes (ACI, CEB-FIP, JSCE etc.). On the other hand, shear cracking behavior in PRC members have barely been understood. The objective of the present study is, therefore, to experimentally explore the shear cracking behavior of PRC beams. Three I-shaped RC and four I-shaped PRC beams were tested under four-point monotonic loading. The experimental program was carried out focusing on the influence of prestressing force, side concrete cover, stirrup spacing, bond characteristics of stirrup and the amount of longitudinal reinforcement on shear crack width. The study revealed that the prestressing force significantly reduced shear crack width in PRC beams as compared to RC beams. In addition, an equation was proposed to calculate shear crack width in RC and PRC members. The proposed formula for shear crack width shows better correlation between calculated values and experimental data than the other formulae. Global RC Structural Damage Index Based on the Assessment of Local Material Damage Sofiane Amziane and Jean Francois Dube Journal of Advanced Concrete Technology, 6(3) 459-468, 2008 Building construction is subjected to service loadings, and sometimes to accidental loadings such as earthquakes inducing severe degradation. Consequently, the evaluation of reinforced concrete structure damage gives adequate help to decide whether or not a structure should be replaced or repaired. This study presents an original way to estimate the state of damage of a construction, using a structural damage index. This index is derived from a local indicator evaluated in critical cross-sections. Comparison between simulations and experimental data give good results in the way to establish the minimum required level for repair. Optimal Maintenance Plan for RC Members by Minimizing Life-Cycle Cost Including Deterioration Risk Due to Carbonation Chien Kuo Chiu, Takafumi Noguchi and Manabu Kanematsu Journal of Advanced Concrete Technology, 6(3) 469-480, 2008 This paper shows deterioration models due to carbonation in consideration of uncertainty to estimate the initiation and the rate of corrosion, and to analyze the structural capacity and serviceability of RC members, i.e. shear capacity, bending strength and width of severe cracking or spalling of columns and beams with corroded reinforcing bars based on simple formulas formed through the past experiments. Then, the failure and severe spalling/cracking probability during earthquakes and the deterioration risk of members in specified years from construction could be evaluated by this method proposed in this paper. In addition, by applying immune algorithm to minimization of life-cycle cost including the deterioration risk, the optimal maintenance plan and semi-optimal solutions with high diversity of reinforced concrete members could also be found in a single analysis and a case study is finally conducted to prove the effectiveness of this system. Probability-Based Maintenance Planning for RC Structures Attacked by Chloride Pakawat Sancharoen, Yoshitaka Kato and Taketo Uomoto Journal of Advanced Concrete Technology, 6(3) 481-495, 2008 In reality, there are many uncertainties relating to the deterioration of reinforced concrete (RC) structure. As a result, actual deterioration degree of structure is found to be not uniform. Currently, various safety factors are considered to cover those uncertainties. This paper proposes a new method for maintenance planning of RC structure that is deteriorated by chloride attack based on probability theory. Prediction models of chloride attack deterioration both of before and after repairing are discussed. Effects of crack and macrocell corrosion were considered to accelerate the deterioration in prediction model. Surface coating, patching repair, cathodic protection, and their combination were considered as repairing options. Moreover, effects of partial and full repair were also considered in the deterioration of repairing system. Actual variation of structural properties, and environmental conditions obtained from inspection program were used directly as input for prediction. By using Monte Carlo simulation, variation of deterioration degree can be predicted. Based on prediction result, repairing and failure cost are determined and used to design the maintenance planning program. Finally, applications of maintenance planning of the actual case studies were given as an example.