Browsing by Author "Lane, D. Stephen"
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- Development of Concrete Shrinkage Performance SpecificationsMokarem, David W. (Virginia Tech, 2002-05-01)During its service life, concrete experiences volume changes. One of the types of deformation experienced by concrete is shrinkage. The four main types of shrinkage associated with concrete are plastic, autogeneous, carbonation and drying shrinkage. The volume changes in concrete due to shrinkage can lead to the cracking of the concrete. In the case of reinforced concrete, the cracking may produce a direct path for chloride ions to reach the reinforcing steel. Once chloride ions reach the steel surface, the steel will corrode, which itself can cause cracking, spalling, and delamination of the concrete. The development of concrete shrinkage performance specifications that limit the amount of drying shrinkage for concrete mixtures typically used by the Virginia Department of Transportation (VDOT) were assessed. Five existing shrinkage prediction models were also assessed to determine the accuracy and precision of each model as it pertains to the VDOT mixtures used in this study. The five models assessed were the ACI 209 Code Model, Bazant B3 Model, CEB90 Code Model, Gardner/Lockman Model, and the Sakata Model. The percentage length change limits for the portland cement concrete mixtures were 0.0300 at 28 days, and 0.0400 at 90 days. For the supplemental cementitious material mixtures, the percentage length change limits were 0.0400 at 28 days, and 0.0500 at 90 days. The CEB90 Code model performed best for the portland cement concrete mixtures, while the Gardner/Lockman Model performed best for the supplemental cementitious material mixtures.
- Evaluation of models for predicting (total) creep of prestressed concrete mixturesMeyerson, Richard M.; Weyers, Richard E.; Mokarem, David W.; Lane, D. Stephen (Virginia Center for Transportation Innovation and Research, 2002-09-01)Concrete experiences volume changes throughout its service life. When loaded, concrete experiences an instantaneous recoverable elastic deformation and a slow inelastic deformation called creep. Creep of concrete is composed of two components, basic creep, or deformation under load without moisture loss and drying creep, or deformation under drying conditions only. Deformation of concrete in the absence of applied load is often called shrinkage. The deformation due to creep is attributed to the movement of water between the different phases of the concrete. When an external load is applied, it changes the attraction forces between the cement gel particles. This change in the forces causes an imbalance in the attractive and disjoining forces. However, the imbalance is gradually eliminated by the transfer of moisture into the pores in cases of compression, and away from the pores in cases of tension. Designs typically use one of the two code models to estimate creep and shrinkage strain in concrete, ACI 209 model recommended by the American Concrete Institute or the CEB 90 Eurocode 2 model recommended by the Euro-International Committee. The AASHTO LRFD is based on the ACI 209 model. Three other models are the B3 model, developed by Bazant; the GZ model, developed by Gardner; and the SAK model developed by Sakata. The objectives of this research was the development of performance limits for compressive creep of concrete mixtures used by the Virginia Department of Transportation, specifically concrete mixtures used for prestressed members (A-5 Concrete) and the determination the accuracy and precision of the creep models presented in the literature. The CEB 90 Eurocode 2 model for creep and shrinkage is the most precise and accurate predictor. The total creep strain for the VDOT portland cement concrete mixtures discussed in this study were found to be between 1200 +/- 110 microstrain at 28 days, and 1600 +/- 110 microstrain at 97 days, at a five percent significant level. It is recommended that the CEB 90 model be used in the AASHTO LRFD rather than the ACI 209 model to improve the prediction of prestress loss.
- Evaluation of the MMLS3 for Accelerated Wearing of Asphalt Pavement Mixtures Containing Carbonate AggregatesDruta, Cristian; Wang, Linbing; Lane, D. Stephen (Virginia Transportation Research Council, 2014-06)The purpose of this study was to develop an accelerated wearing protocol for assessing the susceptibility of asphalt surface mixtures to polishing. This was the second phase of the study. The first phase focused on assessing the characteristics of selected carbonate aggregates available in Virginia that are normally classified as “polishing” and thus not considered suitable for use in pavements except for those roads with an average daily traffic of less than 750 vehicles per day. The selection of aggregates used in pavements is critical in producing surfaces that will continue to provide good skid resistance through a lengthy service life. The specifications of the Virginia Department of Transportation (VDOT) call for “non-polishing aggregate” for use in most surface layers. The study was aimed at making use of locally available polishing aggregates that can reduce the cost of asphalt mixtures while maintaining satisfactory wearing and skid characteristics of the pavements. The objectives of the research were (1) to evaluate the polishing/wear features of mixtures containing limestone aggregate in the laboratory using an accelerated method; (2) to compare friction properties of the laboratory-polished specimens with actual pavement friction measurements; and (3) to compare friction properties of mixtures containing carbonate rock or blends with those of mixtures with non-carbonate rocks. The study included three types of aggregates, i.e., limestone, quartzite, and granite, and blends of these aggregates. The surface mixtures studied were conventional SM-9.5 and SM-12.5 mixtures containing various percentages of limestone, limestone recycled asphalt pavement, and limestone-granite/quartzite blends. The suggested test protocol to evaluate the polishing of asphalt concrete specimens prepared in the laboratory was developed using the third-scale model mobile load simulator (MMLS3). The MMLS3 is capable of applying realistic rolling wheel contact stresses similar to those on highways from the moving traffic. The skid resistance, friction, and texture of actual pavement surfaces and laboratory-fabricated specimens were measured after different polishing intervals. Skid resistance and frictional characteristics were measured by the British pendulum tester, dynamic friction tester, and locked-wheel skid tester; the circular texture meter was used to measure surface macrotexture. Results showed that the MMLS3 can be used to simulate traffic wearing of asphalt concrete specimens of different shapes and sizes in the laboratory including core specimens removed from existing pavements and that the BPT is effective in characterizing changes in friction on specimens that are subjected to simulated trafficking via the MMLS3. Further, test specimens should have a high initial macrotexture and mixtures should have good stability so that the wearing effects are focused on the aggregates. The study recommends that the Virginia Center for Transportation Innovation and Research (VCTIR) work with Virginia Tech and VDOT’s western districts to design and conduct an experiment to explore a series of carbonate / non-carbonate aggregate blends for asphalt mixtures and that the mixture gradations be designed to prevent the absence of macrotexture from impacting the ability to measure the “polish” of the coarse aggregate structure of the experimental mixtures. VCTIR should purchase tires with different tread patterns and try them on the MMLS3 to evaluate the polishing rate of specimens in more detail.
- Methods for Assessing the Polishing Characteristics of Coarse Aggregates for Use in Pavement Surface LayersWang, Linbing; Druta, Cristian; Lane, D. Stephen (Virginia Center for Transportation Innovation and Research, 2010-06-01)The predominant aggregate resources located in the western parts of Virginia are carbonate rocks. The mineral components of these rocks tend to be relatively soft and subject to abrasive wear under traffic that leads to a fairly rapid smoothing of the aggregate surface and the surface of pavements containing them. This smoothing or polishing leads to a loss of surface friction and thus skid resistance of the pavement, creating potential safety issues. As a consequence, surface courses of pavements are constructed with nonpolishing aggregates, which in the western districts can mean lengthy transport of materials. With rising economic and environmental costs associated with transportation, increasing the use of locally available materials through improved methods to discern subtle differences in polishing tendencies or blending of polishing with nonpolishing aggregates could translate into significant cost savings. In this study, a suite of carbonate aggregates suspected to show a range of polishing characteristics based on previous studies was selected for evaluation along with several sources currently used as nonpolishing aggregates. The aggregates were examined petrographically, and the carbonate sources were tested for insoluble residue and subjected to a dilute acid etch to form the basis for a tentative classification of polishing susceptibility. The aggregates were tested in the Micro-Deval apparatus using both the standard procedure for coarse aggregates and a cyclical A/P procedure with silica sand devised for this study to examine how the various aggregate types responded when subjected to various degrees of wearing under similar conditions. Following abrasion cycles, 2-D digital aggregate images were obtained and analyzed using specialized software to assess their morphological properties with emphasis on angularity and surface texture. These properties were assessed before and after abrasion to determine the degree and rate of change in surface texture as well as the texture distribution within an aggregate sample. In addition, pictures were taken of the exposed surfaces of three experimental pavement sections in the Virginia Department of Transportation's Bristol District containing carbonate rock as the fine aggregate blended with nonpolishing coarse aggregate to visually assess the effect of traffic in the last 3 years. The carbonate rocks evaluated could be grouped according to polishing and wear tendency based on petrographic characteristics and mass loss in the Micro-Deval tests. Although visual distinctions could be discerned, these differences were not identified statistically by the image analysis program, but factors affecting the program were identified. A second phase of work is proposed that focuses on developing an accelerated pavement wearing protocol for assessing polishing tendencies and evaluating various mixtures of carbonate and nonpolishing aggregates.
- Portable Image Analysis System for Characterizing Aggregate MorphologyWang, Linbing; Lane, D. Stephen; Lu, Yang; Druta, Cristian (Virginia Center for Transportation Innovation and Research, 2008-02-01)In the last decade, the application of image-based evaluation of particle shape, angularity and texture has been widely researched to characterize aggregate morphology. These efforts have been driven by the knowledge that the morphologic characteristics affect the properties and ultimate performance of aggregate mixtures in hot-mixed asphalt, hydraulic cement concrete and bound and unbound pavement layers, yet the lack of rapid, objective, and quantitative methods for assessment have inhibited their application in the engineering process. Developed systems for computer-based imaging and image analysis can cost up to $30-40,000 and are usually not portable to the field. However, recent advances in technology have produced pocket computers having as much processing power as was available in some desktop computers. This project takes advantage of these advances to develop an inexpensive portable image analysis system for characterizing aggregate morphology. The system was developed with an integral pocket computer-high resolution camera but can also use individual components consisting of a digital camera and lap- or desk-top computer. Digital images of aggregate particles are captured with the camera. These images are analyzed within the Matlab software program environment with a macro developed and written for this project that uses Fast Fourier Transform to characterize the particle morphology with respect to three parameters: shape, angularity and texture, based on the particle perimeter (outline or edge). By analyzing a number of particles from a source, it can be characterized with respect to these three parameters. Following development of the analysis program, 10 coarse aggregates from various Virginia sources were analyzed. Particles of each aggregate were randomly chosen so that each group contained the various shapes and textures representative of the source. Three images of each particle were obtained at distances of 2, 3, and 10 in to evaluate the resolution needed for adequate analysis. The reliability of the image processing was assessed by statistically analyzing the shape, angularity, and texture values to determine how the threshold parameter affects the particle edge acquisition. Asymptotic analysis was performed to determine the number of images needed to obtain a statistically stable value for each aggregate parameter. It was determined that images acquired at close range (2 or 3 in) were needed to provide sufficient resolution to adequately characterize the aggregate. It was also found that statistically valid values for aggregate shape, angularity, and texture can be obtained from fifteen particle images of random orientation. It can be concluded that the system can be successfully used to characterize coarse aggregate morphology. It is recommended that the Virginia Department of Transportation's Materials Division begin collecting images of aggregates used statewide and collaborate with the VTRC to perform the characterizations and build the database of aggregate morphologic characteristics. This information, coupled with performance testing of the materials, will provide the basis for incorporating the characterization parameters into specifications and guide material usage in the future.
- Structural load testing and flexure analysis of the Route 701 Bridge in Louisa County, VirginiaCousins, Thomas E.; Lucas, Jeremy L.; Brown, Michael C.; Stephen R. Sharp; Lane, D. Stephen (Virginia Center for Transportation Innovation and Research, 2004-06-01)A continuous slab bridge in Louisa County, Virginia, on Route 701 developed a planar horizontal crack along the length of all three spans. This project was designed to determine if the current load rating of the bridge could be raised and to document the behavior and stiffness of the bridge to serve as a benchmark for possible future tests, which may determine if there is progressive damage attributable to crack growth. These objectives were accomplished through field tests performed in November 2003. One truck (loaded to three different weights) was used to perform static and dynamic tests on the bridge, and the truck was oriented in three test lanes. Vertical displacement gages (deflectometers) attached to the underside of the bridge slab were used to measure deflections during the truck passes. The recorded deflections were analyzed and normalized to document the behavior of the bridge. The values were also compared to estimated design values in accordance with the AASHTO Standard Specifications for Highway Bridges. Under the testing loads, the bridge behaved elastically, and thus raising the load rating of the bridge was considered safe. The deflections and process are presented to allow comparisons with future tests to determine if there is progressive damage to the bridge attributable to crack growth.