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CONTENTS
Volume 7, Number 1, February 2010
 

Abstract
A simplified method, developed from the softened strut-and-tie model, for determining the mid-span deflection of deep beams at ultimate state is proposed. The mid-span deflection and shear strength predictions of the proposed model are compared with the experimental data collected from 70 simply supported reinforced concrete deep beams, loaded with concentrated loads located at a distance a from an end reaction. The comparison shows that the proposed model can accurately predict the mid-span deflection and shear strength of deep beams with different shear span-to-depth ratios, different concrete strengths, and different horizontal and vertical hoops.

Key Words
deep beams; reinforced concrete; deflection; shear strength.

Address
Wen-Yao Lu: Dept. of Interior Design, China University of Technology, Taipei, Taiwan 11695, R.O.C.
Shyh-Jiann Hwang: Dept. of Civil Engineering, National Taiwan University, Taipei, Taiwan 10617, R.O.C.
Ing-Jaung Lin: Dept. of Construction Engineering, National Taiwan University of Science and Technology, Taipei, Taiwan 10672, R.O.C.

Abstract
This research aimed to investigate the influence of high-volume mineral admixtures (MAs), i.e., fly ash and slag, on the hydration characteristics and microstructures of cement pastes. Degree of cement hydration was quantified by the loss-on-ignition technique and degree of pozzolanic reaction was determined by a selective dissolution method. The influence of MAs on the pore structure of paste was measured by mercury intrusion porosimetry. The results showed that the hydration properties of the blended pastes were a function of water to binder ratio, cement replacement level by MAs, and curing age. Pastes containing fly ash exhibited strongly reduced early strength, especially for mix with 45% fly ash. Moreover, at a similar cement replacement level, slag incorporated cement paste showed higher degrees of cement hydration and pozzolanic reaction than that of fly ash incorporated cement paste. Thus, the present study demonstrates that high substitution rates of slag for cement result in better effects on the short- and long-term hydration properties of cement pastes.

Key Words
cement paste; mineral admixtures; hydration; microstructures.

Address
Chao-Wei Tang: Dept. of Civil Engineering & Engineering Informatics, Cheng-Shiu University, No. 840, Chengcing Road, Niaosong Township, Kaohsiung County, Taiwan, R.O.C.

Abstract
The system of pores of autoclaved aerated concrete (AAC) is described by the so-called cherry-pit model, a random system of partially interpenetrating spheres. For the simulation of fracture processes, the solid phase is approximated by an irregular spatial network of beams obtained by means of the so-called radical tessellation with respect to the pore spheres. FE calculations using standard software (ANSYS) yield the strain energies of the beams. These energies are used as fracture criterion according to which highly loaded beams are considered as broken and are removed from the network. The paper investigates the relationship between mean fracture strength and microstructure for structures close to real AAC samples and virtual structures with particular geometrical properties.

Key Words
porous material; spherical pores; fracture strength; equivalent network; FE simulation; strain energy.

Address
I. Kadashevich: Otto-von-Guericke-Universitat Magdeburg, Institut fur Experimentelle Physik, Leipziger Str. 44, 39120 Magdeburg, Germany
D. Stoyan: TU Bergakademie Freiberg, Institut fur Stochastik, 09596 Freiberg, Germany

Abstract
Dredged silt from reservoirs in southern Taiwan was sintered to make lightweight aggregates (LWA), which were then used to produce high-performance lightweight aggregate concrete (HPLWC). The HPLWC was manufactured using different amounts of mixing water (140, 150, and 160 kg/m3) and LWA of different particle densities (700, 1100, and 1500 kg/m3) at different W/b ratios (0.28, 0.32, and 0.4). Results show that the lightweight aggregates of dredged silt taken in southern Taiwan perform better than the general lightweight aggregates. In addition, the HPLWC possessed high workability with a slump of 230-270 mm, and a slump flow of 450-610 mm, high compressive strength of over 40 MPa after 28 days of curing, good strength efficiency of cement exceeding 0.1MPa/kg/m3, low thermal conductivity of 0.4-0.8 kcal/mhoC, shrinkage of less than 4.8

Key Words
dredged silt; high-performance lightweight aggregate concrete (HPLWC); workability; durability.

Address
H.Y. Wang and Y.N. Sheen: Dept. of Civil Engineering, National Kaohsiung University of Applied Sciences,Kaohsiung, Taiwan, R.O.C.
M.F. Hung: Dept. of Civil Engineering, De-Lin Institute of Technology, Taipei, Taiwan, R.O.C.

Abstract
We present the shape determination method of 3-D reinforcement corrosion based on observed temperature on concrete surface. The non-destructive testing for reinforcement corrosion in concrete using a heat image on concrete surface have been proposed by Oshita. The position of the reinforcement of corrosion or the cavity can be found using that method. However, the size of those defects can not be precisely measured based on the heat image. We therefore proposed the numerical determination system of the shape for the reinforcement corrosion using the observed temperature on the concrete surface. The adjoint variable method is introduced to formulate the shape determination problem, and the finite element method is employed to simulate the heat transfer problem. Some numerical experiments and the examination for the number of the observation points are shown in this paper.

Key Words
reinforcement corrosion; observed temperature on concrete surface; shape determination problem; adjoint variable method; finite element method.

Address
Takahiko Kurahashi: Dept. of Mechanical Engineering, Nagaoka University of Technology, 1603-1 Kamitomioka-cho, Nagaoka-shi, Niigata, 940-2188, Japan
Hideki Oshita: Dept. of Civil Engineering, Chuo University, 1-13-27 Kasuga, Bunkyou-ku, Tokyo, 112-8551, Japan

Abstract
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Key Words
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Address
Jianzhong Lai: Dept. of Materials Science and Engineering, Nanjing University of Science and Technology, Nanjing 210094, China
Wei Sun: College of Materials Science and Engineering, Southeast University, Nanjing 211189, China


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