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Riding K.A.,Kansas State University | Poole J.L.,CTL Group | Folliard K.J.,University of Texas at Austin | Juenger M.C.G.,University of Texas at Austin | Schindler A.K.,Auburn University
ACI Materials Journal | Year: 2011

Some predictive models for concrete temperature development and strength depend on the application of the Arrhenius equation to characterize the progress of hydration, which in turn requires an apparent activation energy E a value to define the temperature sensitivity of the hydration reactions. Testing to determine Ea can be very time-consuming and expensive. It would be useful to have a model that estimates Ea for a given concrete mixture. To be broadly applied, such a model must account for the variable chemistry of cementitious systems. This paper describes the development of a model for Ea using multi-variate statistics analysis of experimental hydration data from 116 cementitious mixtures. The model was also validated by an independent set of hydration data from six different cementitious mixtures. The model accounts for the effects of cement chemistry, supplementary cementitious materials, and chemical admixtures. Copyright © 2011, American Concrete Institute. All rights reserved. Source

Grasley Z.C.,Texas A&M University | DAmbrosia M.D.,CTL Group
Cement and Concrete Composites | Year: 2011

Passive restrained concrete ring experiments provide enough information to extract useful aging viscoelastic constitutive properties when combined with free drying shrinkage and mass loss experiments. In this paper, analytical techniques are described for deriving a closed-form solution to extract the viscoelastic Young's modulus from solidifying concrete in a restrained concrete ring test. Using limit theorems, approximate closed-form solutions are derived for the non-uniform internal relative humidity (RH), free drying shrinkage, and tangential stress gradients. An example problem demonstrates the utility of the derived solutions and illustrates the effect that viscoelastic relaxation and solidification have on the tangential stress profile in the restrained, drying concrete ring. Both viscoelastic and solidification effects have a significant impact on the predicted stress profile. © 2010 Elsevier Ltd. All rights reserved. Source

When applied appropriately, NDT techniques can be used to test large concrete structures with confidence. NDT causes the least disruption and provides valuable information about the structural condition, beyond that which can be seen by the inspector's eye. Application of each technique must be planned and carefully thought out based on the specific structural geometry, accessibility and evaluation objective. Indepth knowledge and experience of the applied test technique is required to make sound interpretation of collected data. When feasible, trial testing or mock-ups are very beneficial in defining a suitable test program. As power plants age, potential deterioration of concrete infrastructure prompts the need for structural and durable evaluation in association with relicensing applications. Further, when structures fail to perform in accordance with design expectations, investigation into the root cause often includes application of concrete NDT. Application of these technologies in the energy industry is expected to increase in the upcoming years. Source

Li L.,University of Tennessee at Knoxville | Ma Z.,University of Tennessee at Knoxville | Griffey M.E.,University of Tennessee at Knoxville | Oesterle R.G.,CTL Group
Journal of Bridge Engineering | Year: 2010

This paper focuses on an investigation of improved continuous longitudinal joint details for decked precast prestressed concrete girder bridge systems. Precast concrete girders with an integral deck that is cast and prestressed with the girder provide benefits of rapid construction along with improved structural performance and durability. Despite these advantages, use of this type of construction has been limited to isolated regions of the United States. One of the issues limiting more widespread use is a perceived problem with durability of longitudinal joints used to connect adjacent girders. This paper presents the results of a study to assess potential alternate joint details based on constructability, followed by testing of selected details. Seven reinforced concrete beam specimens connected with either lapped headed reinforcement or lapped welded wire reinforcement were tested along with a specimen reinforced by continuous bars for comparison. Test results were evaluated based on flexural capacity, curvature at failure, cracking, deflection, and steel strain. Based on the survey and the experimental program, a headed bar detail with a 152 mm (6 in.) lap length was recommended for replacing the current welded steel connector detail. © 2010 ASCE. Source

Bassam A.,CTL Group | Iranmanesh A.,University of Illinois at Chicago | Ansari F.,University of Illinois at Chicago
Engineering Structures | Year: 2011

Conventional methods for displacement based condition assessment of bridges solely rely on the maximum level of displacements experienced by the piers, and do not take into account the accumulated damage that result from cyclic loading. More advanced approaches take this into account by considering the structural damage as a linear combination of the normalized maximum displacements and hysteretic energy. Computation of the dissipated hysteretic energy requires monitoring of the lateral forces during the seismic events, which are not as practical as monitoring bridge pier deformations. This article reports on the development of a simple damage assessment method that considers the effect of cyclic loading on the state of damage and it is merely based on monitoring the bridge pier deformations. A fiber optic displacement serial array was designed for measuring the crack opening displacement reversals at the plastic hinge areas. © 2011 Elsevier Ltd. Source

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