Comparison of Linear Temperature Corrections and Activation Energy Temperature Corrections for Electrical Resistivity Measurements of Concrete
Alex Coyle, Oregon State UniversityShow Abstract
Robert Spragg, SES Group & Associates LLC at Turner-Fairbank Highway Research Center
Armen Amirkhanian, Oregon State University
Prannoy Suraneni, Oregon State University
Jason Weiss, Oregon State University
Electrical resistivity measurements are being increasingly used as measurements for concrete acceptance in practice. It has been shown that these measurements are sensitive to temperature. This paper examines the influence of temperature on electrical resistivity measurements in concrete. Two commonly used approaches for temperature corrections were evaluated: a linear temperature correction approach (α) and an activation energy based temperature correction approach (Ea‑cond). These approaches were compared with each other and their predictive capabilities were assessed using measured data from various concrete mixtures. It was found that for cases of low temperature sensitivity, the predictions obtained with α and with Ea‑cond were very similar. However, the Ea‑cond approach was found to provide more accurate corrections than corrections using α for measurements conducted at lower temperatures and for systems with higher temperature sensitivities. For saturated concrete specimens, both the linear (α) and activation energy (Ea‑cond) approaches are acceptable while the use of Ea‑cond approach provides better predictive capabilities in sealed concrete specimens, especially at low temperatures. Average values for E a‑cond were found to be 22.7 kJ/mol for sealed specimens and 15.8 kJ/mol for saturated specimens, and corresponding average values of α are 2.75 %/°C and 2.00 %/°C, respectively. The saturated values are closer to what may be expected of a pore solution on its own.
Postcrack Performance of Structural Fiber-Reinforced Concrete for Concrete Overlays
Manik Barman, University of Minnesota, Twin CitiesShow Abstract
Bryce Hansen, University of Minnesota, Duluth
Thomas Burnham, Minnesota Department of Transportation
Maria Masten, Minnesota Department of Transportation
Structural fibers are used in thin concrete overlays to enhance their service life. These fibers can improve the post-crack and load transfer performances of thin concrete overlays which can eventually reduce the severity of cracking and joint faulting. However, little guidance is available to the pavement industry on the selection of fibers. Moreover, because of lack of research studies, the currently available design procedures for concrete overlays do not accurately account for the contribution of fibers.
In the current study, the post-crack performances of ten different types of commercially available fibers have been evaluated in terms of residual strength ratio in flexural testing. A total of thirty-one concrete mixes were tested. It was found that the residual strength ratio is highly influenced by the fiber volume fraction, geometry of the fibers (e.g., straight, crimped, embossed, twisted, etc.), aspect ratio (fiber length divided by the effective diameter) and stiffness. This study has developed a correlation between a fiber reinforcement index and the residual strength ratio. Using this correlation, an approximate fiber dosage can be estimated for a target residual strength ratio. Moreover, the findings from this study will be useful when accounting for the post-crack benefits of structural fibers in future thin concrete overlay design procedures.
Performance Evaluation of Concrete Pavement Slab Considering Creep Effect by Finite Element Analysis
Ya Wei, Tsinghua UniversityShow Abstract
Creep, as the intrinsic property of concrete material, will inevitably affect the performance of concrete pavement slabs in the field. However, the creep effect on performances of concrete pavement slabs is far from being fully investigated. In this study, a test set-up is designed to measure the flexural creep of concrete beams exposed to both sealed and drying conditions. The measured flexural creep results are then modeled by the microprestress solidification theory-based creep model which is incorporated into finite element analysis to evaluate numerically the creep effect on the moisture warping deformation, warping stress, and the total stress under traffic load in concrete slabs. It is found that concrete creep has significant effect on slab performance. According to the concrete creep measured in this study, the warping deformation of slabs can be reduced by 7.6%-61.5%, and the warping stress and the total stress can be relaxed by at least 50%. The extents of the creep effect on warping and stress relay on slab size, thickness, and subgrade modulus. This study provides a realistic numerical methodology to the current performance evaluation of concrete slabs in the field, and the effect of concrete creep can not be ignored.
Bridge Substructure Repairs with Self-Consolidating Concrete and Galvanic Anodes
H. Celik Ozyildirim, Virginia Department of TransportationShow Abstract
Stephen Sharp, Virginia Transportation Research Council
Historically, the Virginia Department of Transportation (VDOT) has repaired chloride-contaminated reinforced concrete bridge substructure elements that contain vertical and overhead sections with either shotcrete or a conventional A3 (3,000 psi) or A4 (4,000 psi) concrete. This study investigated using self-consolidating concrete (SCC), which has a high flow rate, bonds well, has low permeability, and provides smooth surfaces, as another option. SCC can be placed in narrow areas and can fit the geometry of the element.
The study also explored the use of galvanic anodes to control corrosion activity in SCC repairs at various locations. In VDOT’s Lynchburg District and Staunton District, SCC repairs were made with and without the use of galvanic anodes. This provided a means for determining the benefit of using the anodes. The needed repair areas were determined by visual observation and sounding.
After 7 years of service, SCC repair areas with and without anodes did not exhibit corrosion activity; small vertical cracks were evident in the SCC but did not affect performance. The anodes provided protection to the steel immediately adjacent to the repair areas. However, they did not protect the more remote unrepaired concrete areas. These unrepaired areas now require additional repairs.
The study recommended that in the future half-cell potential measurements, rather than sounding, be used to identify the needed repair areas. Progression of corrosion demonstrates the necessity of removing all chloride-contaminated concrete adjacent to the reinforcement, as anodes in the repair area will provide protection only in a narrow area around the patch.