Albert M Bleakley

Improving Properties of Reclaimed Asphalt Pavement for Roadway Base Applications Through Blending and Chemical Stabilization

Finding innovative ways to incorporate reclaimed asphalt pavement (RAP) into highway base course applications will provide both environmental and economic benefits by allowing in situ recycling of material for projects such as widening or shoulder addition. RAP is a well-drained granular material; however, 100% RAP has low bearing strength and creeps under load. The objective of this research is to develop methods to improve RAPs strength while reducing creep to an acceptable level through blending with high-quality crushed-limestone aggregate, by chemical stabilization with asphalt emulsion or portland cement, or both. RAP–aggregate blends with and without chemical stabilization were compacted by the modified Proctor method, cured, and tested for strength and creep. Strength was tested by the limerock bearing ratio (LBR), a variant of the California bearing ratio test. Specimens were tested dry and soaked to evaluate retained strength. One-dimensional creep testing was performed with 7-day oedometer tests. RAP–aggregate blends have the potential to be used successfully as base course material. Blends of RAP with 50% limerock base material attained acceptable LBR strength and creep with the addition of 1% of either asphalt emulsion or cement. Blends of RAP with 75% or more limerock attained close-to-acceptable LBR and low levels of creep without any chemical stabilizer. Significant variability was noted between results with different blends and stabilizing agents. Performance testing should be conducted to establish the suitability of a specific RAP–aggregate blend.

Evaluating Laboratory Compaction Techniques of Reclaimed Asphalt Pavement

Reclaimed asphalt pavement (RAP) is a byproduct of roadway resurfacing. A limited amount of RAP can be recycled into new hot-mix asphalt; the rest is stockpiled. Some states allow the use of RAP–aggregate blends as base course material. Because of RAPs low strength and susceptibility to creep deformation, the Florida Department of Transportation (DOT) excludes RAP from being used as pavement base course for high-traffic areas. The research objective was to determine whether the strength characteristics of RAP could be improved through compaction and thereby make its base suitable in high-traffic areas. Modified Proctor, vibratory, and gyratory compaction data were compared. Four RAP sources were used. Specimens compacted by the three methods were tested with the limerock bearing ratio (LBR), unconfined compressive strength, and indirect split tensile strength. LBR is Floridas variation of the California bearing ratio. Specimens were compacted to either a density or a compaction energy level. Vibratory compaction produced the lowest densities and strengths. Modified Proctor produced higher densities and strengths than vibratory, but the LBR strengths for all RAP types were consistently below Florida DOT standards. Gyratory compaction produced the highest densities and strengths. Gyratory RAP specimens were two to four times as strong as modified Proctor specimens at the same density. The compaction method did not have as significant an effect on creep, although gyratory-compacted samples produced less creep than modified Proctor–compacted samples.

Strength and Creep Characteristics of Reclaimed Asphalt Pavement-Sand Blend Backfill in Mechanically Stabilized Earth Walls

Using reclaimed asphalt pavement (RAP) as a backfill for mechanically stabilized earth (MSE) walls provides both environmental and economic benefits by allowing in situ recycling for road widening projects. RAP, a well-drained granular material, has lower reinforcing strip pullout strength than A-3 sand and creeps under constant load. The objective of this research was to determine whether blending RAP with A-3 sand would improve RAPs performance in MSE applications. Laboratory specimens of 100% RAP, 100% A-3 sand, and 50% RAP–50% sand blends were compacted by the modified Proctor method and tested for vertical creep with one-dimensional oedometer compression tests at three stress levels to simulate different depths behind an MSE wall. Large-scale test pit testing was performed to determine reinforcing strip ultimate lateral pullout strength; pullout creep at 25%, 50%, and 75% of ultimate pullout; and vertical creep at the three overburden stress levels used in laboratory testing. RAP–sand blends had higher density, friction factors, and pullout strength and developed ultimate pullout strength at lower displacements than either 100% sand or 100% RAP. The RAP–sand blends exhibited more horizontal and vertical creep than 100% sand but significantly less creep than 100% RAP.