David W Mokarem

Comparing Resilient Modulus and Dynamic Modulus of Hot-Mix Asphalt as Material Properties for Flexible Pavement Design

With the current trend toward developing mechanistic flexible pavement design and the need for more reliable design procedures, accurate characterization of hot-mix asphalt (HMA) properties is needed. Resilient and dynamic modulus tests were performed at five temperatures on two typical mixes used in the Commonwealth of Virginia to compare the test results. The dynamic modulus was measured at six frequencies at each of the testing temperatures, and the resilient modulus test was performed at one loading time. The study found that the size of the specimen statistically affected the measured resilient modulus value. Resilient modulus values obtained in the 100-mm-diameter specimens were higher than those obtained in the 150-mm-diameter specimens at all testing temperatures. No statistical differences were observed in the resilient modulus of the two mixes. However, statistical differences were found in the dynamic modulus of the two mixes. A strong relation between the dynamic modulus test performed at 5 Hz...

Field Investigation of Corrosion-Protection Performance of Bridge Decks Constructed with Epoxy-Coated Reinforcing Steel in Virginia

The corrosion-protection performance of epoxy-coated reinforcing steel (ECR) in three 17-year-old bridge decks in Virginia was assessed. The decks had an upper mat of ECR and a lower mat of bare steel. Surface cracking in the right traffic lane was visually surveyed and 12 cores randomly located in the lowest 12th percentile cover depth in each deck were drilled. The concrete core and the extract ECR were visually inspected. In the concrete moisture content, absorption, percent saturation, carbonation depth, and the effective chloride diffusion constant were measured. In the ECR physical damage, coating thickness, adhesion loss and corrosion at damaged sites, and undercoating corrosion at adhesion test sites were measured. The chloride content of the concrete and carbonation of the ECR trace were determined. Significant coating adhesion loss occurred before the chloride arrived at the bar depth. The debonding of the epoxy is wet debonding, which is predicted by the negative thermodynamic work of adhesion. ECR will extend the service life of only 5 percent of the bridge decks in Virginia. Thus, its use is not cost-effective. Additional decks should be evaluated to confirm the results of this and other studies.

Accuracy of Ground-Penetrating Radar for Estimating Rigid and Flexible Pavement Layer Thicknesses

In this paper, the accuracy of ground-penetrating radar (GPR) for estimating pavement layer thicknesses is studied on the basis of the investigation of 17 pavement sites in Virginia. The considered sites have different types of pavement systems (flexible, continuously reinforced, jointed concretes, and composite) and different ages (0 to 5 years; 10 to 15 years; older than 20 years with a surface less than 10 years; and older than 20 years with a surface older than 10 years). Because of the diversity of the test sections considered, the accuracy of the GPR thicknesses was studied for pavement age for the same type of pavement and against pavement type for sites of the same age category. For flexible pavements, the GPR thickness error was found to increase as the pavements age increased (4.4% error for pavements 0 to 5 years old versus 5.8% error for pavements older than 20 years with surfaces older than 10 years). Moreover, for the same age category, flexible pavements were found to have a relatively hig...

Vacuum Saturated Absorption As Aggregate Durability Indicator

Aggregate durability testing is the subject of this paper. The testing is necessary to achieve a durable concrete by accurately selecting the most durable coarse aggregates. The authors note that the time-consuming and labor-intensive nature of this testing can see both increased efficiency and a reduction in cost by a corresponding reduction in the number of required tests. In exploring this hypothesis, the authors conduct an in-depth study analyzing the aggregate durability testing methods used by the Wisconsin Department of Transportation (WisDOT). Results show that much of the required testing for aggregates having vacuum saturated absorptions (VSAs) of less than 2% could be eliminated. In the case of coarse aggregates having VSAs of less than 2%, several tests (micro-deval, LA abrasion, sodium sulfate soundness, and confined or unconfined freezing and thawing) have been found to be unnecessary.

Development of performance specifications for shrinkage of portland cement concrete

During its service life, concrete experiences volume changes. One of the types of deformation experienced by concrete is shrinkage. There are four main types of shrinkage associated with concrete: plastic, autogenous, carbonation, and drying shrinkage. The volume changes in concrete from shrinkage can lead to the cracking of the concrete. In the case of reinforced concrete, cracks in the cover concrete provide a direct path for chloride ions to reach and corrode the reinforcing steel. The development of concrete drying-shrinkage performance specifications with an associated test procedure was assessed for concrete mixtures purchased by the Virginia Department of Transportation (VDOT). 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 are the ACI 209 Code model, CEB90 Code model, Bazant B3 model, Gardner–Lockman model, and Sakata model. The percentage length change limits for the portland cement concrete mixtures were found to be 0.0300% at 28 days and 0.0400% at 90 days. The CEB90 Code model was judged as the best prediction model for the VDOT portland cement concrete mixtures.

Performance Evaluation of Bonded Concrete Pavement Overlays After 11 Years

Concrete overlays were placed on continuously reinforced concrete (CRC) pavement sections of I-295 near Richmond, Virginia, and I-85 near Petersburg, Virginia. A 2-in. bonded portland cement concrete overlay on I-295 was placed to prevent spalling attributable to improper steel depth of the existing CRC pavement, and a 4-in. bonded portland cement concrete overlay on I-85 was placed to increase the structural capacity of the pavement. The CRC pavements were in reasonably good condition when the overlays were placed. Evaluations of the bonded overlays were conducted immediately after their placement in 1995, in 1999, and in 2006 after 11 years in service. The evaluations included bond strength testing between the overlay and the CRC pavement, chain drag testing to detect delamination between the overlays and the pavement, falling weight deflectometer testing to assess the in situ structural capacity of the bonded overlay pavement sections, permeability testing to determine the permeability conditions of the overlays, and skid resistance testing to check the surface texture conditions. The bonded concrete overlays performed well after 4 and 11 years. The results indicate that bonded overlays extended the life of the existing CRC pavements and are expected to last 20 years or more. The experience gained during 11 years is documented and the use of bonded concrete overlays is recommended where the design life can be realized.

Shrinkage of Latex-Modified and Microsilica Concrete Overlays

Shrinkage performance was examined of Virginia Department of Transportation-approved latex-modified and microsilica concrete overlay mixtures. Research was conducted on both field-sampled and laboratory-fabricated restrained and unrestrained specimens. From crack and delamination surveys of sampled bridge decks and laboratory test results, a shrinkage performance-based specification for the Virginia Department of Transportation was developed. There was no significant difference between the unrestrained shrinkage values of latex-modified and microsilica concrete overlay mixtures for the specified time periods. Restrained microsilica concrete specimens generally cracked earlier and more frequently than restrained latex-modified concrete specimens. However, the bridge deck crack and delamination surveys show that conditions and quality of construction and type and frequency of traffic may have a greater effect on cracking than the overlay material.