Volume 10, No. 1, 2 and 3 Enhanced Model and Simulation of Hydration Process of Blast Furnace Slag in Blended Cement Yao Luan, Tetsuya Ishida, Toyoharu Nawa and Takahiro Sagawa Journal of Advanced Concrete Technology, 10, 1-13, 2012 A hydration model for cementitious materials was applied to slag blended cement. The original model was found to overestimate the hydration degree of slag, and the influence of the slag ratio on the hydration degree not to be well simulated either. The hydration mechanism of slag was investigated, considering the role of calcium hydroxide as activator and the Ca/Si ratio of C-S-H. It is assumed that for low Ca/Si ratio, the C-S-H inner product has a stronger resistance against ion diffusion and thus influences the hydration process significantly. Accordingly an enhanced model for slag hydration is proposed. Finally, the enhanced model is verified by both hydration degree and heat generation tests. Effect of Stirrups on the Shear Failure Mechanism of Deep Beams Yasar Hanifi Gedik, Hikaru Nakamura, Yoshihito Yamamoto, Naoshi Ueda and Minoru Kunieda Journal of Advanced Concrete Technology, 10, 14-30, 2012 The purpose of this study is to clarify the effect of stirrups in deep beams by investigating the shear failure mechanism analytically by using the 3-D Rigid-Body-Spring Model analytical tool. The investigation of the analytical results of the internal stress state and 3-D deformations of deep beams were the key objectives of this study. Firstly, the applicability of the analytical tool on deep beams was confirmed by comparison of analytical and experimental results. Then, the stirrup contribution to load carrying capacity of deep beams was investigated and the shear failure mechanism based on the B and D region concept was clarified analytically. To achieve this, analytical results such as stress distribution, 3-D deformations, crack patterns and strain of stirrups were investigated. Three types of stirrup effect were observed in deep beams. In the a/d= 0.5 case, the peak load increase due to the confinement effect of stirrups. In the a/d=1.0 case, the stirrup contributes to the strut action that leads to an increase in load. In the case of a/d < 1.0, the D region is dominant. On the other hand, the peak load increases significantly with increases of stirrup ratio in the case of a/d > 1.5, in which the truss analogy is dominant rather than the strut action. Microwave Absorption Characteristics of a Carbon-Containing Electrically Conductive Concrete in a Multimode Cavity Brandon Chambers, Christopher A. Pickles and Peter J. Tumidajski Journal of Advanced Concrete Technology, 10, 31-40, 2012 The microwave absorption characteristics of both powdered and rectangular blocks of an electrically conductive concrete were measured and compared to a normal Portland cement concrete in a multimode cavity. The variables investigated were: irradiation time, sample mass and incident power for the powdered samples and sample orientation, water additions and multiple irradiations for the block samples. The results were quantified in terms of the microwave absorption efficiency (ηa). The absorption efficiency of the electrically conductive concrete was significantly higher than the Portland cement control concrete. For both of the concretes, hot spot formation occurred in the vicinity of the corner of the block. For the electrically conductive concrete this phenomenon took place close to the surface and resulted in combustion of the carbon and disintegration of the concrete. For the normal Portland cement concrete, the hot spot formed below the surface where fracturing, degradation and melting occurred. Experimental Damage Identification in Concrete Structure Using Stack Migration Imaging Technology Ying Luo, Ziping Wang and Baiqiang Xu Journal of Advanced Concrete Technology, 10, 41-46, 2012 Stack migration imaging technology (SMIT), an advanced data processing technique typically used in geophysical exploration, was employed for the detection of small cracks inside concrete structures. Ultrasonic transducers were utilized as both actuator and sensor to generate and receive stress waves in the concrete. The wave field reflected from the damage was synthesized at a common reflective point to highlight the effective signals by using multiple transducers. Two concrete specimens with embedded damage were examined using horizontal stacking technology and diffracting scan pre-stack migration technology, respectively. The dimensions and locations of the damage were successfully imaged. Compared with traditional ultrasonic detection, The experimental results show that SMIT offers better damage visualization and allows damage detection from one side of the specimen. An Investigation into the Long-Term Excessive Deflection of PC Viaducts by Using 3D Multi-scale Integrated Analysis Motohiro Ohno, Nobuhiro Chijiwa, Benny Suryanto and Koichi Maekawa Journal of Advanced Concrete Technology, 10, 47-58, 2012 This paper investigates the causes of excessive long-term deflection of PC bridge viaducts by using 3D integrated material-structural analyses to take into account the coupled chemo-physics at various scales from the molecular size of water to the structural members. The excessive deflection observed at site is found to be rooted in the deformation of cement paste stemming from both externally applied loads and internal stresses driven by capillary surface tension and disjoining pressures in micro-pores. Not only the former but also the later effect is focused in the serviceability control of PC viaducts. It is found that the nonlinear, long-term deflection of the bridge viaduct can be approximately separated into the components of deflections provoked by external mechanistic and internal thermodynamic actions, even though each component is nonlinearly associated with the thermodynamic states of moisture in micro-pores of cement hydrates. Autogenous and Drying Shrinkage of Fibre Reinforced High-Performance Concrete Drago Saje, Branko Bandelj, Jakob Šušterši?, Jože Lopati? and Franc Saje Journal of Advanced Concrete Technology, 10, 59-73, 2012 This paper reports the results of laboratory investigations into the time history of the shrinkage of fibre reinforced high-performance concrete with 0.25%, 0.50% and 0.75% by volume of longer IRI 50/30 or shorter IRI 50/16 steel fibres or polypropylene fibres. To allow suitable comparisons, measurements of the shrinkage of a comparable plain concrete were also performed. The results of the measurements of the autogenous shrinkage of the tested composites and of the comparable plain concrete at early and later ages of the specimens are presented. The results of the performed laboratory tests show that the use of steel fibres is more effective for the reduction of early autogenous shrinkage than that of dry polypropylene fibres. For the reduction of later autogenous shrinkage, the polypropylene fibres are almost as effective as the steel fibres. The least drying and total shrinkage of the composites at later ages occur in the case when polypropylene fibres are used. Effects of PFA and GGBS on Early-Ages Engineering Properties of Portland Cement Systems Xiang Ming Zhou, Joel R. Slater, Stuart E. Wavell and Olayinka Oladiran Journal of Advanced Concrete Technology, 10, 74-85, 2012 A comprehensive study is presented on the effects of pulverised fly ash (PFA) and ground granulated blast furnace slag (GGBS) on early-age engineering properties of Portland cement (PC) systems. It has been found that partially replacing PC by PFA or GGBS resulted in longer setting times but better workability with PFA exhibiting more prominent effect than GGBS. As the replacement level increased, the setting of both PFA and GGBS pastes further delayed but workability of concrete was enhanced. PFA concretes exhibited consistently lower compression and splitting tensile strengths than PC ones. As the replacement level increased, strengths decreased. At the replacement level up to 30% by mass, GGBS concrete exhibited higher splitting tensile strength than PC concrete. However, as the replacement level further increased, it developed lower strength than PC concrete up to 21 days. Then, it managed to gain higher splitting tensile strength than PC concrete at the replacement levels up to 70% by mass at 28 days. Both PFA and GGBS can reduce drying shrinkage and the reduction effects became more significant as replacement level increased with GGBS performing better than PFA. Adding fibres into PFA concrete increased its splitting tensile strength and further reduced its drying shrinkage. Effect of the Key Mixture Parameters on Tortuosity and Permeability of Concrete Shamsad Ahmad, Abul Kalam Azad and Kevin F. Loughlin Journal of Advanced Concrete Technology, 10, 86-94, 2012 The primary aim of this paper is to study the effect of key mix parameters on tortuosity and permeability of concrete' s pore system, the two important material properties related to concrete durability. The measurement of tortuosity requires determination of porosity and pore size of concrete. Eighteen different concrete mixes were prepared by varying the levels of the key mix parameters, namely water/cement ratio, cement content and coarse/fine aggregate ratio, and then tested to determine porosity, pore size, tortuosity, and permeability. The experimental data were used to study the effect of the key mix parameters on porosity, tortuosity and permeability of concrete. While all the selected parameters of mix design have some influence on tortuosity of the pore system and permeability, the most dominant one is the water/cement ratio, which can be rated as the single most significant parameter. Test data also show that permeability decreases with increasing tortuosity, but the decrease is marginal with tortuosity of the pore system exceeding a value of 150. A Fuzzy Classification System for Evaluating the Health Condition of Marine Concrete Structures Masoud Dehghani Champiri, S. Hossein Mousavizadegan and Faramarz Moodi Journal of Advanced Concrete Technology, 10, 95-109, 2012 This paper presents a new classification system called the Marine Structure Health index (MSHi). An evaluation model based on the fuzzy Delphi analytic hierarchy process (FDAHP) has been used for estimation of health in marine concrete structures. For this purpose, fifteen types of cracking in concrete, surface distresses, and miscellaneous distresses have initially been investigated and rated. In the MSHi system, a number from 0 to 100 is assigned to the health of a structure. Based on the MSHi classification, the health of a structure is classified into five modes from the view point of distress: very poor, poor, medium, good and very good. Sustainable Concrete made of Construction and Demolition Wastes using Recycled Wastewater in the UAE Mohamed Elchalakani and Elgaali Elgaali Journal of Advanced Concrete Technology, 10, 110-125, 2012 Most of the previous research on the use of recycled materials for concrete examined only the effect of using recycled aggregate in concrete mixes. In this paper, the combined effects of recycled aggregate and recycled water on the strength and durability of recycled concrete are presented and discussed. Three types of mixing water were examined and found to comply with the requirements of EN 1008 and ASTM C94. The test program involved the preparation of a moderate strength concrete made out of recycled water and recycled aggregate obtained from demolition and construction wastes. In the demolition waste series, four mixes of concrete were prepared using different contents of aggregate extracted from demolition waste and recycled water. The effect of the recycled aggregate and recycled water on the axial and flexural strength was found to be moderate but had a significant negative impact on the durability. In the construction waste series, to enhance the durability and to lower the carbon footprint of the recycled concrete mix, the OPC was replaced by GGBS. Four replacement ratios, 60%, 70%, 80%, and 90%, of the OPC were examined. While all the four mixes achieved good strength and durability, the mix with 90% GGBS did not achieve the target strength of 40 MPa even after 56 days. In general, fully recycled concrete mix with 80% GGBS replacement is recommended for any sustainable future construction in the Gulf with an expected carbon footprint of 129.9 kg/m3. Strain Energy Frame Impact Machine (SEFIM) Tuan Kiet Tran and Dong Joo Kim Journal of Advanced Concrete Technology, 10, 126-136, 2012 This paper proposes an innovative Strain Energy Frame Impact Machine (SEFIM) designed to explore direct tensile behavior of High Performance Fiber Reinforced Cementitious Composites (HPFRCC) at high strain rates. The proposed system utilizes an energy frame to store a large amount of elastic strain energy as well as to suddenly generate high rate tensile impact pulse. The prototype of SEFIM demonstrated that the proposed energy frame could store enough elastic strain energy to fail a large-sized tensile specimen at high strain rates in direct tension. The tensile stress versus strain curve of HPFRCC under high rate impact was obtained by using the prototype with the aid of a high speed camera system and dynamic strain gauges attached on the surfaces of the transmitter bar.