Developing a Mixture Design Specification for Flexible Base Construction (0-6621-1)

In the Texas Department of Transportation (TxDOT), flexible base producers typically generate large stockpiles of material exclusively for TxDOT projects. This large "state-only" inventory often maintained by producers, along with time requirements for testing and reduced manpower within TxDOT offices, resulted in this project's investigation into a mixture-design specification for flexible base. The goals of this project are to develop a flexible base specification that reduces TxDOT's burden for sampling and testing, reduces time and space burdens on producers for maintaining TxDOT-only stockpiles, and maintains or improves the quality of the base. To facilitate accomplishing these goals, this project developed a draft quality control/quality assurance (QC/QA) specification for flexible base. Based on a thorough review of background information, sampling and testing placeholders for placement and production aggregate and mixture tests were selected and incorporated into a classical QC/QA format draft specification. While the current draft specification largely uses existing TxDOT test procedures, improvements may be realized by considering the Grace methylene blue method and the use of index tests as surrogates for modulus and permanent deformation properties. The methylene blue method may be able to better control the quantity and amount of fines, while linking index tests to mechanistic properties could enable acceptance testing better linked to design assumptions. The second year of this project will sample and test flexible base quarries around the state to determine material variability that is attainable in the real world without compromising the design strength.