ACPA Directs Research to Improve Dowel Specifications
ACPA and the National Concrete Consortium have been working to develop specifications that can be used by manufacturers and agencies to guide the development and implementation of more efficient and durable dowels for concrete pavement.
Current AASHTO M254 and T253 specifications were developed decades ago and are directly applicable only to 1.25-in. diameter epoxy-coated steel dowels. Industry innovations featuring different materials and structural shapes, along with different dowel coatings, have driven the need for specifications that can quantify the potential performance benefits of these new and improved products.
One key component of dowel specifications is their ability to evaluate the structural behavior of joints containing different dowel products. It has been recognized that a new test was needed to evaluate dowel groups rather than single dowels because different dowels could have different optimal installation configurations due to differences in size, shape, and component materials and these could not be adequately evaluated using a single-dowel test. This led to a proposal to modify the current T253 structural test to include a four-foot-wide test specimen with dowel groups in each joint (rather than the single dowel in each joint for the current T253 test).
The different specimen configuration required different loading (a simulated 9000-lb wheel load at the slab corner instead of the original 4000-lb distributed load). The different loading configuration and specimen shape meant that joint deflections would be different than in the original T253 test, even if 1.25-in. diameter epoxy-coated steel dowels were used. Analytical models were used to estimate the joint deflections for both test protocols using the standard epoxy-coated dowel, but testing was needed to validate and calibrate those analytical models for “real-world” conditions.
This testing was accomplished at CTLGroup last week under ACPA supervision and with funding provided by CP Tech Center. Data from these tests are being compiled and analyzed for incorporation in a new set of “universal” dowel specifications that are built on the current AASHTO M254 and T253 specifications.
The new specifications have been developed with the input of various NCC member agencies, ACPA staff (national and chapter/state) and dowel manufacturers. We anticipate the new specifications will be released for wider review and comment early this summer, with possible promotion for AASHTO adoption soon afterward. (Special thanks to Mark Snyder, Ph.D., P.E., for compiling this report.)