Tack coats are particularly important for a paving process. A tack coat can be defined as a thin layer of bituminous liquid that is applied as an emulsion, cutback, or paving grade asphalt onto an existing asphalt or concrete pavement prior to an overlay and/or between layers of new asphalt paving lifts. A tack coat is applied to promote bonding. Adequate bonding between the pavement lifts and the existing road/milled surface, and an overlay is crucial.
A tack coat allows the completed pavement structure to behave as a single unit rather than independent layers. Without a tack coat, inadequate bonding between layers can result in:
- Delamination
- Slippage and shoving
- Longitudinal wheel path cracking
- Fatigue cracking and
- Rutting
The loss of fatigue life for the new overlay has been shown to be 50% fatigue loss with only 10% bond loss and 60%-75% fatigue loss when no tack coat is utilized.
Using a tack coat is considered a cost-effect assurance to support the pavements design life. Due to the importance of a good-quality tack coat, Blueline Transportation and Road Products developed and manufactures a product known as High Performance Tack Coat- HPTC.
HPTC is a non-tracking tack coat designed with conventional overlays in mind and with higher performance than other tack coat products. The material can be applied in cooler weather and at night and still break within 15 to 30 minutes. This allows the contractor to start paving sooner with less cleanup of equipment at the end of the day. The emulsion is applied in its manufactured form with no dilution required.
As a high performance tack coat HPTC provides:
- Faster drying time
- Better bonding
- Non-tacky
- Better application control – 0.08 to 0.10 gallons per square yard
- Better compaction
- Night paving
The recommended application rates for HPTC is:
| Surface type | Residual Rate (gsy) | App. Bar rate Undiluted (gsy) | App. Bar Rate Diluted 1:1 (gsy) |
| New Asphalt | 0.020-0.045 | 0.030-0.065 | 0.060-0.130 |
| Existing Asphalt | 0.040-0.070 | 0.060-0.105 | 0.120-0.210 |
| Milled Surface | 0.040-0.080 | 0.060-0.120 | 0.120-0.240 |
| Portland Cement Concrete | 0.030-0.050 | 0.045-0.075 | 0.090-0.150 |
For more information on how HPTC can work for your project, please contact a Blueline sales engineer at 503-279-2600.
References:
Johnson, Dave P.E., Tackling tack coats: Answers to common questions
Asphalt Magazine 2015 (Asphalt Institute) http://asphaltmagazine.com/tackling-tack-coats/
TX DOT 2001Â https://pavementinteractive.org/reference-desk/construction/site-preparation/tack-coats/