Construction Details and Initial Performance of Two High-Performance Base Sections

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. In Project 0-4358 draft specifications (proposed Item 245) were developed for high-performance flexible base materials. These specifications tighten all existing specifications, place an upper limit of 10 percent on the amount of material passing the No. 200 sieve, and introduce new procedures to ensure that the base is not moisture susceptible. In project 5-4358-01 two TxDOT pavements containing bases that met the proposed high-performance base specifications were constructed. No handling or segregation problems were encountered. The main concern found by the contractors was the use of nuclear density gauges for measuring density. Alternative methods were investigated. The initial field moduli were measured to be 60 ksi. The long-term benefits of these low-fines bases could not be demonstrated in this short project, since all the applicable sections are new and performing well. However performance problems were encountered on a third section constructed on SH 43. In that case the design caused a "bath-tub" effect and water became trapped in the low fines base. Based on this experience a "day-lighting" requirement was placed in the Item 245 specification. High-performance bases will cost more than traditional bases, and they are not needed in many areas of west Texas where rainfall is low. However, these bases will be economically viable in many areas of northeast Texas, especially with the escalating prices of traditional road building materials.