New Generation Mix-Designs: Laboratory Testing and Construction of the Apt Test Sections

摘要

Recent changes to the Texas HMA mix-design procedures such as adaption of the higher PG asphalt-binder grades and the Hamburg test have ensured that the mixes routinely used on the Texas highways are not prone to rutting. However, performance concerns have been raised about these mixes, which are now drier, more difficult to compact, and more susceptible to cracking. This is particularly problematic with the dense-graded Type C and D mixes that are widely used throughout the State of Texas. Consequently, several new ideas are under consideration to either modify the existing mix-design criteria (target densities, VMA requirements, etc.) and/or to include new and simpler cracking test procedures. Of primary focus in this research project is the comparative evaluation of the following three mix-design procedures and making recommendations thereof: (1) the modified volumetric mix-design procedure; (2) the Hamburg (rutting) and Overlay (cracking) test based balanced mix-design procedure; and (3) a simplified balanced mix-design procedure with a simpler alternative cracking test. The research methodology and scope of work incorporates extensive literature review of the existing mix-design procedures, laboratory testing, and field validation including accelerated pavement testing (APT) and performance monitoring. This interim report provides a preliminary overview of the mix-designs and laboratory test evaluations of three commonly used Texas mixes (namely Type B, Type C, and Type D) based on the Texas gyratory, volumetric, and balanced mix-design procedures. As well as conducting round-robin tests in six different Texas laboratories to quantify the Overlay test variability and repeatability, the laboratory tests also included comparative evaluation of various cracking tests such as the indirect tension, direct uniaxial tension, and semi-circular bending. HMA mix workability and compactability tests for quantifying the constructability aspects of the mixes were also conducted and are discussed in this report. Construction details of the APT test sections are also discussed in this interim report.