Evaluation of design and construction issues of thin HMA overlays.

Details

• Creators:
  Wilson, Bryan ; Scullion, Tom ; Faruk, Abu
• Corporate Creators:
  Texas A&M Transportation Institute
• Corporate Contributors:
  United States. Federal Highway Administration ; Texas. Dept. of Transportation
• Subject/TRT Terms:
  • Hot mix paving mixtures
  • Aggregates
  • Asphalt mixtures
  • Overlays (Pavements)
  • Mix design
  • Friction tests
  • Laboratory tests
  • Evaluation
  • Bond strength (Materials)
  • Permeability
  More +
• Publication/ Report Number:
  FHWA/TX-15/0-6742-1
• Resource Type:
  Tech Report
• Geographical Coverage:
  Texas
• Corporate Publisher:
  Texas A&M Transportation Institute
• Abstract:
  While the overall implementation of thin HMA overlays in Texas has been successful, some issues need to be addressed: ; appropriate blending of SAC A and SAC B aggregate to ensure adequate skid resistance; best practices to achieve adequate bonding ; (surface prep and tack coats); and correct quality assurance test methods to achieve adequate compaction. The purpose of this ; research, therefore, was to address these concerns through laboratory and field testing. In addition, preliminary work to refine a crack ; propagation model for thin overlays was performed. ; Laboratory friction testing considered samples with two gradation types, four aggregates types, and five levels of aggregate ; blending. Samples were polished with simulated traffic in the lab and tested with the dynamic friction tester. Results show the terminal ; polish value for all designs with 100 percent SAC B replacement failed, as had designs with 50 and 75 percent blending of one SAC ; B+ and one marginal SAC B aggregate. SAC B replacement up to 25 percent was acceptable for all aggregates. ; Shear and tensile strength tests were developed to measure interlayer bond strength. A computer model suggested the maximum ; shear stress at a bonded thin-overlay interface is 120 psi. Bond strength tests were performed on laboratory samples made with two ; base mix types, two thin overlay types, 5 tack types (including non-tracking tacks), 3 tack rates, simulated milling, and moisture ; conditioning. Bond strength was most dependent on the mix type being bonded and compaction effort, and less on tack type and tack ; rate. In the tensile strength tests and half the shear tests, non-tracking tacks had higher strengths than samples using CSS-1H or no ; tack. No single non-tracking tack was found to have better performance than others. Variable tack rates of CSS-1H were only ; significant on dense-graded mixes. Low and moderate levels of tack provided the best bond. Milled samples had higher strength than ; unmilled samples in shear. A tack tracking test was developed to discern different non-tracking times during curing. ; Four compaction quality assurance test methods were used on three thin overlay projects. Properties measured were flow time with ; the current TxDOT permeability test, surface dielectric with high-frequency ground penetrating radar, mean profile depth (MPD) with ; the circular-track meter, and bulk density from field cores. Correlations of the tests were strong on a project-by-project basis, but ; generally not good when combining the data sets. Flow Time-MPD, Flow Time-Core Voids, and Surface Dielectric-Core Voids were ; best correlations overall. ; TTI provided support to TxDOT on many new thin overlay demonstration projects, ranging from mix design, performance testing, ; construction method recommendations, and bonding testing. Hand working of on TOM-B project caused problems with mat thickness ; and compaction uniformity. Using tack did not influence bond strength except for one fine-permeable friction course in shear testing. ; Thermal segregation problems were noted on two projects. ; Recommendations are contained in the draft specifications, including aggregate blending guidelines, bond strength testing, micromilling, ; and minimum and maximum flow times for compaction quality control.
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• Format:
  PDF
• Funding:
  Project 0-6742
• Download URL:
  https://rosap.ntl.bts.gov/view/dot/28790/dot_28790_DS1.pdf
• File Type:
  [PDF - 8.26 MB]
• Collection(s):
  US Transportation Collection
• Main Document Checksum:
  urn:sha256:3c7c4fd9d12944ed1c88f71a95c580a6b821d8c7f0ac71206c6c67b0b9149e23