Heavy-Duty Flexible Bases: Field Performance and Draft Specifications (0-4358-4)

Traditional Texas flexible bases specified under Item 247 perform well as long as they are kept dry. However, rapid and sudden failures can occur if water enters these bases. The source of the moisture susceptibility problems is the fine clay in these bases. One base in this study contained over 2 percent Smectite, a highly expansive clay mineral. The concept of heavy-duty bases resolves around (a) controlling the type and amount of fine material and (b) requiring a high-strength rock. In project 4358 laboratory and field studies were conducted. The use of heavy-duty bases with fines contents between 5 and 10 percent requires modifications to laboratory testing, design, and field construction procedures. Three TxDOT projects containing bases which met the proposed heavy-duty base specifications were monitored in this study. The long-term benefits of these low-fines bases could not be demonstrated in this short study, as all the applicable sections are new and performing well. However, the oldest section on FM-1810 in the Fort Worth District has higher long-term modulus than the control Item 247 base section. This report includes a draft construction specification (Item 245) for consideration on future heavy-duty base projects. This specification is based on recommendations from Texas district laboratory engineers. Heavy-duty bases will cost more than traditional bases, and they are not required in many areas of west Texas where rainfall is low. However, these bases will be economically viable in many areas of Northwest Texas, especially with the escalating prices of traditional road building materials.