• Journal of the Korea Concrete Institute
• /
• v.16 no.6 s.84
• /
• pp.875-881
• /
• 2004

The quality of recycled aggregate is affected by original concrete strength and the manufacturing process of recycled aggregates. In this study, the porosity of old and new mortar, and the compressive strength of concrete were investigated to examine the influence of recycled aggregate on the concrete. Six kinds of recycled coarse aggregates were produced from concrete blocks of differing strength levels (A:60. 1MPa, B:41.7MPa, C:25.5MPa). Original concrete strength and the bond mortar of recycled aggregate influences the pore structures of both old and new mortar. The pore size distribution of old mortar was found to be greatly affected by age, and the reduction of the porosity of bond mortar on low strength recycled aggregate increased at a greater rate than that of bond mortar on high strength recycled aggregate. The pore size distribution of new mortar in recycled aggregate concrete changed in comparison with that of new mortar in virgin aggregate concrete. The total porosity of new mortar using B level recycled aggregates was smaller than that of new mortar with A, and C level recycled aggregates. Moreover, the compressive strength of recycled aggregate concrete was found to have been affected by original concrete strength. The compressive strength of concrete only changed slightly in the porosity of new mortar over $15\%$, but increased rapidly in the porosity of new mortar fewer than $15\%$.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2001.11a
• /
• pp.433-438
• /
• 2001

In recent years, the construction methods of precast prestressed concrete beam bridges by using tendon have been increasingly proposed. The properties of flexural tensile strength between precast prestressed concrete beam and cast-in-place concrete is an important factor that affects the structural performance. This paper aims at evaluating the tensile strength between old and new concrete. Tensile strength gain, with age after placing new concrete was evaluated. Test results show that the tensile strength between old and new concrete is much smaller than that of monolithic concrete. Also, it is shown that the curing condition of concrete has the tremendous effect on tensile strength.

• Structural Engineering and Mechanics
• /
• v.38 no.4
• /
• pp.503-516
• /
• 2011

Uncertainty in concrete properties, including concrete modulus of elasticity and modulus of rupture, are predicted by developing a microstructural homogenization model. The homogenization model is developed by analyzing a concrete representative volume element (RVE) using the finite element (FE) method. The concrete RVE considers concrete as a three phase composite material including: cement paste, aggregate and interfacial transition zone (ITZ). The homogenization model allows for considering two sources of variability in concrete, randomly dispersed aggregates in the concrete matrix and uncertain mechanical properties of composite phases of concrete. Using the proposed homogenization technique, the uncertainty in concrete modulus of elasticity and modulus of rupture (described by numerical cumulative probability density function) are determined. Deflection uncertainty of reinforced concrete (RC) beams, propagated from uncertainties in concrete properties, is quantified using Monte Carlo (MC) simulation. Cracked plane frame analysis is used to account for tension stiffening in concrete. Concrete homogenization enables a unique opportunity to bridge the gap between concrete materials and structural modeling, which is necessary for realistic serviceability prediction.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2004.05a
• /
• pp.746-749
• /
• 2004

A new-type of FRP-concrete composite bridge deck system is proposed and its behaviors are experimentally studied. The new-typedeck consists of FRP as a permanent form and main tension resisting member and concrete as a compression resisting member. A suitable bonding method such as silica coating is applied to the interface between FRP and concrete to ensure composite behavior. The proposed deck system uses the box-shape FRP member, while a typical FRP-concrete composite deck uses the I-shape FRP member. Theproposed deck system has inherent advantages of a FRP-concrete composite deck like corrosion free and easy construction. The new-type deck shows the equal performances compared to a previous one, and has the advantage of reducing self-weight. In this study, the static tests on 3-span FRP-concrete decks in full scale are carried out, so that load-displacement relation, stress distribution, failure mode and design criteria are analyzed. The test results show that the deflection design criterion (L/800, L: span length) is satisfied at the service load state. No concrete tensile crack occurs in the negative moment region above the main girder, regardless of no tensile reinforcement at upper concrete portion.

• Computers and Concrete
• /
• v.3 no.2_3
• /
• pp.91-102
• /
• 2006

To place concrete overlays has become a standard application in the strengthening and rehabilitation of concrete structures such as bridges, tunnels, parking decks and industrial buildings. In general, connectors are used to ensure a monolithic behavior of the two concrete layers. Within the framework of the development of a new connector wedge splitting tests and shear tests were performed, in addition nonlinear finite element analyses were applied to investigate the load transfer behavior of the connectors for different prototypes. The numerical simulation results were compared to experimental data. The computed load-displacement curve demonstrates good correspondence with the curves obtained in the experiments, and the experimental crack patterns are reasonably simulated by the computed crack propagation. Both numerical and experimental investigations on the wedge splitting test and on the shear test served as basis for the development of new type of connectors.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.29 no.3
• /
• pp.230-234
• /
• 2009

As concrete ages, the surrounding environment is expected to have growing influences on the concrete. As all the impacts of the environment cannot be considered in the strength-estimating model of a nondestructive concrete test, the increase in concrete age leads to growing uncertainty in the strength-estimating model. Therefore, the variation of the model error increases. It is necessary to include those impacts in the probability model of concrete strength attained from the nondestructive tests so as to build a more accurate reliability model for structural performance evaluation. This paper reviews and categorizes the existing strength-estimating statistical models of nondestructive concrete test, and suggests a new form of the strength-estimating statistical models to properly reflect the model uncertainty due to aging of the concrete. This new form of the statistical models will lay foundation for more accurate structural performance evaluation.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2002.05a
• /
• pp.349-354
• /
• 2002

Significant improvements in bond strength between new and existing concrete can be achieved through the modification of the new concrete by latex modification. But, no test method has been adopted as a standard to measure the bond strength between the concrete used to repair and the substrate being repaired. The performance of old and the new concrete construction depends upon bond strength between old and the new concrete. Current adhesion strength measurement method ignores the effect of stress concentration by shape of specimens. Therefore, this research calculates stress concentration coefficient using finite element analysis and direction tensile strength test (pull-off test). The result shows that the required core depth is 2.5cm. Elastic modulus and overlay thickness do not influence in stress concentration.

• Computers and Concrete
• /
• v.7 no.2
• /
• pp.87-102
• /
• 2010

This paper discusses new capabilities developed for the Virtual Penetration Laboratory (VPL) software package to address the challenges of determining Penetration Resistance (PR) equations for concrete materials. Specifically, the paper introduces a three-invariant concrete constitutive model recently developed by the authors. The Advanced Fundamental Concrete (AFC) model was developed to provide a fast-running predictive model to simulate the behavior of concrete and other high-strength geologic materials. The Continuous Evolutionary Algorithms (CEA) automatic fitting algorithms used to fit the new model are discussed, and then examples are presented to demonstrate the effectiveness of the new AFC model. Finally, the AFC model in conjunction with the VPL software package is used to develop a PR equation for a concrete material.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2001.11a
• /
• pp.1109-1114
• /
• 2001

This paper describes an attempt to develop a new truss model for reinforced concrete beams failing in shear based on a rational behavioral model. The key idea incorporated with truss model is the internal force state factor which is able to express global state of internal force flow in cracked reinforced concrete beams subjected to shear and bending. A new truss model using internal force state factor may provide a comprehensive result of shear strength in reinforced concrete beams without web reinforcement.

• Steel and Composite Structures
• /
• v.28 no.5
• /
• pp.527-539
• /
• 2018

The use of reinforced concrete (RC) shear wall with concrete filled steel tube (CFST) columns and steel fiber reinforced concrete (SFRC) shear wall has aroused widespread attention in recent years. A new shear wall, named SFRC shear wall with CFST columns, is proposed in this paper, which makes use of CFST column and SFRC shear wall. Six SFRC shear wall with CFST columns specimens were tested under cyclic loading. The effects of test parameters including steel fiber volume fraction and concrete strength on the failure mode, strength, ductility, rigidity and dissipated energy of shear wall specimens were investigated. The results showed that all tested shear wall specimens exhibited a distinct shear failure mode. Steel fibers could effectively control the crack width and improve the distribution of cracks. The load carrying and energy dissipation capacities of specimens increased with the increase of steel fiber volume fraction and concrete strength, whilst the ductility of specimens increased with the increase of steel fiber volume fraction and the decrease of concrete strength.