About the project:

There have been considerable research efforts conducted, in recent years, at local and national levels to investigate the effect of material characteristics as well as design techniques on the performance of chip seals. In addition, with the advancement of technology, new materials and additives have been introduced into the construction market with the goal of enhancing the performance of chip seals. Despite these advances, and the long history of chip seal use on its roadway network, the Virginia Department of Transportation (VDOT) has not undertaken a thorough review of its chip seal practices in more than 25 years. The objective of this research study will be to evaluate VDOT’s single layer (single layer and modified single layer) chip seal practices from a materials characterization and design perspective.

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About the project:

Mass concrete elements are usually heavily reinforced and subject to large thermal change as the concrete cures.  The definition of mass concrete is generally based on the minimum dimension of the element but is more complicated because of the many factors involved.  High heat retention in mass concrete causes differential and high temperatures that can result in detrimental cracks.  In some applications of mass concrete, high strengths or early strengths are needed, requiring increases in cementitious material contents beyond the usual low amount of cementitious materials needed in mass concrete to keep the temperature from rising too high during cement hydration.  Typically, concretes with regular consistency measured by slump test are used in mass concrete elements.  However, congestion of the reinforcement in the element combined typically with geometric and placement constraints require concretes with high flow rates, as in self-consolidating concrete (SCC).  Such concretes generally have high cementitious material contents for flowability and stability.  There is a conflict in the amount of cementitious materials between mass concrete which requires low cementitious contents to control temperature rise and the use of high cementitious contents for early or high strengths and high workability.  The cementitious material contents include supplementary cementitious materials, fly ash and slag cement, for durability and to reduce portland cement contents for temperature control. The objective of this study is to investigate and optimize mass concrete mixtures with regards to temperature control and high workability.  Also, the definition of mass concrete will be refined in ways that are helpful to VDOT in taking precautions to avoid problems that can arise during placement and curing.

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About the project:

The Virginia Department of Transportation (VDOT) is operating a variable speed limit (VSL) system on I-95 northbound between mileposts 115 and 130, south of Fredericksburg.  The goal of the VSL system is to improve both safety and operations on this congested section of highway by encouraging speed harmonization, more uniform speed selection, dampening the effects of shockwaves, and providing advance warning of congestion. This project will continue the evaluation of the safety and operational impacts of the VSL system to determine benefits during the first year of operations.  Performance measures will include changes in crashes, travel time reliability, delay, throughput, and speed compliance.  The overall benefit-cost ratio of the system will be examined as well.

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Co-Principal Investigators

About the project:

The Virginia Department of Transportation (VDOT) currently requires the use of the Indirect Tensile Cracking Test (IDT-CT) as specified in ASTM D8225-19 in its Balanced Mix Design (BMD) specification to assess the cracking susceptibility of dense-graded asphalt surface mixtures (SM) with “A” (PG64S-22) and “D”(PG64H-22) designations (i.e., 0 to 3 million equivalent single axle load [ESAL] range for A mixtures and 3 to 10 million ESAL range for D mixtures). A current performance criterion requiring a minimum cracking tolerance (CT) index of 70 was recommended to alleviate the cracking susceptibility of the asphalt mixtures based on extensive mixture testing. This CT index was determined based on testing of compacted specimens from reheated plant-produced asphalt mixtures. Although the current cracking testing protocol and its threshold value (i.e., CT index of 70) in VDOT’s BMD specification is indicative of the cracking performance of asphalt mixtures, it does not account for how the performance of asphalt mixtures throughout the service life is affected by oxidative aging (i.e., as it experiences long-term aging). Thus, laboratory evaluation of the long-term oxidative aging characteristics of asphalt mixtures is essential to ensure that the asphalt mixtures within the pavement structures continue to perform adequately throughout their service life. The objective of this research is twofold: (I) to develop practical long-term aging protocols for asphalt SMs with A and D designations that can be used in mix design verification and production of asphalt mixtures for quality control and acceptance purposes; and (II) to develop preliminary performance criteria for CT index for the to-be-developed long-term aging protocols. 

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