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CONTENTS
Volume 11, Number 2, February 2013
 

Abstract
The use of rock wool waste, an industrial by-product, in cement-based composites has positive effects on the environment because it reduces the problems associated rock wool disposal. The experiments in this study tested cement-based composites using various rock wool waste contents (10, 20, 30 and 40% by weight of cement) as a partial replacement for Portland cement in mortars. The pozzolanic strength activity test, flow test, compressive strength test, dry shrinkage test, absorption test, initial surface absorption test and scanning electron microscope observations were conducted to evaluate the properties of cement-based composites. Test results demonstrate that the pozzolanic strength activity index for rock wool waste specimens is 103% after 91 days. The inclusion of rock wool waste in cement-based composites decreases its dry shrinkage and initial surface absorption, and increases its compressive strength. These improved properties are the result of the dense structure achieved by the filling effect and pozzolanic reactions of the rock wool waste. The addition of 30% and 10% rock wool wastes to cement is the optimal amount based on the results of compressive strength and initial surface absorption for a w/cm of 0.35 and 0.55, respectively. Therefore, it is feasible to utilize rock wool waste as a partial replacement of cement in cement-based composites.

Key Words
rock wool waste; pozzolanic strength activity index; initial surface absorption test; waste treatment

Address
Wei-Ting Lin: Dept. of Civil Engineering, National Ilan University, 1 Shen-Nong Road, Ilan 26047, Taiwan; nstitute of Nuclear Energy Research, Atomic Energy Council, Executive Yuan, 1000 Wenhua Road, Longtan 32546, Taiwan; An Cheng: Dept. of Civil Engineering, National Ilan University, 1 Shen-Nong Road, Ilan 26047, Taiwan; Ran Huang and Ta-Yuan Han: Dept. of Harbor and River Engineering, National Taiwan Ocean University, 2 Pei-Ning Rd., Keelung 20224, Taiwan; Yuan-Chieh Wu: Institute of Nuclear Energy Research, Atomic Energy Council, Executive Yuan, 1000 Wenhua Road, Longtan
32546, Taiwan

Abstract
This paper investigates the parameters that control the design of Fiber Reinforced Polymer (FRP) reinforced concrete flexural members proportioned following the ACI 440.1R-06. It investigates the critical parameters that control the flexural design, such as the deflection limits, crack limits, flexural capacity, concrete compressive strength, beam span and cross section, and bar diameter, at various Mean-Ambient Temperatures (MAT). The results of this research suggest that the deflection and cracking requirements are the two most controlling limits for FRP reinforced concrete flexural members.

Key Words
GFRP; steel; flexural strength; deflection; cracking; reinforcement ratio

Address
Fares Jnaid and Riyad Aboutaha: Department of Civil and Environmental Engineering, Syracuse University, Syracuse, NY, USA

Abstract
The nonlinear finite element method with eight noded isoparametric quadrilateral element for concrete and two noded element for reinforcement is used for the prediction of the behavior of reinforcement concrete structures. The disturbed state concept (DSC) including the hierarchical single surface (HISS) plasticity model with associated flow rule with modifications is used to characterize the constitutive behavior of concrete both in compression and in tension which is named DSC/HISS-CT. The HISS model is applied to shows the plastic behavior of concrete, and DSC for microcracking, fracture and softening simulations of concrete. It should be noted that the DSC expresses the behavior of a material element as a mixture of two interacting components and can include both softening and stiffening, while the classical damage approach assumes that cracks (damage) induced in a material treated acts as a void, with no strength. The DSC/HISS-CT is a unified model with different mechanism, which expresses the observed behavior in terms of interacting behavior of components; thus the mechanism in the DSC is much different than that of the damage model, which is based on physical cracks which has no strength and interaction with the undamaged part. This is the first time the DSC/HISS-CT model, with the capacity to account for both compression and tension yields, is applied for concrete materials. The DSC model allows also for the characterization of non-associative behavior through the use of disturbance. Elastic perfectly plastic behavior is assumed for modeling of steel reinforcement. The DSC model is validated at two levels: (1) specimen and (2) practical boundary value problem. For the specimen level, the predictions are obtained by the integration of the incremental constitutive relations. The FE procedure with DSC/HISS-CT model is used to obtain predictions for practical boundary value problems. Based on the comparisons between DSC/HISS-CT predictions, test data and ANSYS software predictions, it is found that the model provides highly satisfactory predictions. The model allows computation of microcracking during deformation leading to the fracture and failure; in the model, the critical disturbance, Dc, identifies fracture and failure.

Key Words
Reinforced concrete; cracks; fracture; tension-compression behavior; disturbed state concept; plasticity; finite element analysis; softening behavior; validations

Address
A.H. Akhaveissy: Department of Civil Engineering, Faculty Engineering, Razi University, P.O. Box: 67149–67346, Kermanshah, Iran; C.S. Desai: Department of Civil Engineering and Engineering Mechanics, University of Arizona, Tucson, AZ 85721, U.S.A.; D. Mostofinejad: Department of Civil Engineering, Isfahan University of Technology, Isfahan-Iran; A. Vafai: Department of Civil Engineering, Sharif University of Technology, Tehran-Iran

Abstract
The complete stress-strain behavior of steel fiber reinforced concrete in compression is needed for the analysis and design of structures. An experimental investigation was carried out to generate the complete stress-strain curve of high-performance steel fiber reinforced concrete (HPSFRC) with a strength range of 52–80 MPa. The variation in concrete strength was achieved by varying the water-to-cementitious materials ratio of 0.40-0.25 and steel fiber content (Vf = 0.5, 1.0 and 1.5% with l/d = 80 and 55) in terms of fiber reinforcing parameter, at 10% silica fume replacement. The effects of these parameters on the shape of stress-strain curves are presented. Based on the test data, a simple model is proposed to generate the complete stress-strain relationship for HPSFRC. The proposed model has been found to give good correlation with the stress-strain curves generated experimentally. Inclusion of fibers into HPC improved the ductility considerably. Equations to quantify the effect of fibers on compressive strength, strain at peak stress and toughness of concrete in terms of fiber reinforcing index are also proposed, which predicted the test data quite accurately. Compressive strength prediction model was validated with the strength data of earlier researchers with an absolute variation of 2.1%.

Key Words
compressive strength; high-performance concrete; crimped steel fiber; fiber reinforcing index; stress-strain curve; toughness; modeling

Address
P. Ramadoss: Department of Civil Engineering, Pondicherry Engineering College, Puducherry-605014, India; K. Nagamani: Structural Engineering Division, Anna University, Chennai-600 025, India

Abstract
One of the major benefits of the pre-stressed concrete pavements is the omission of tension in concrete that results in a reduction of cracks in the concrete slabs. Therefore, the life of the pavement is increased as the thickness of the slabs is reduced. One of the most important issues in dealing with the prestressed concrete pavement is determination of the magnitude of the pre-stress. Three dimensional finite element analyses are conducted in this research to study the pre-stress under various load (Boeing 777) and thermal gradient combinations. The model was also analyzed under temperature gradients without the presence of traffic loading and the induced stresses were compared with those from theoretical relationships. It was seen that the theoretical relationships result in conservative values for the stress.

Key Words
thermal stress; pre stressed concrete pavement; finite element

Address
Fereidoon Moghadas Nejad and Sepehr Ghafari: Department of Civil and Environmental Engineering, Amirkabir University of Technology, Tehran, Iran; Shahriar Afandizadeh: Department of Civil and Environmental Engineering, University of Science and Technology, Tehran, Iran


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