United States Department of Transportation
i
Risk management of low air void asphalt concrete mixtures.
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2013-07-01
[PDF-2.56 MB]
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NTL Classification:NTL-HIGHWAY/ROAD TRANSPORTATION-Pavement Management and Performance;NTL-HIGHWAY/ROAD TRANSPORTATION-Design;
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Abstract:Various forms of asphalt pavement distress, such as rutting, shoving and bleeding, can be attributed, in many cases, to low air voids in
the mixtures during production and placement. The occurrence of low air void contents during plant production may originate as a result
of an accidental increase in binder content or mix fines (or both). When low air voids are encountered during production, the specifying
agency must decide whether to require the material that has already been placed to be removed and replaced or whether it can be left
in place with a reduction in pay. Consequently, the Indiana Department of Transportation (INDOT) initiated this research project to
develop a decision‐support tool for dealing with such events that is based on projected rutting performance of the pavement system.
The study was conducted along three paths. In the first, INDOT sponsored two pavement test sections at the National Center for Asphalt
Technology (NCAT) Test Track. The second path involved testing mixes in the INDOT Accelerated Pavement Testing (APT) Facility. In both
cases, mixtures were produced in local hot mix plants by either increasing the fines content or the binder content. The NCAT test
sections included low void mixes in the surface course only and performance was measured by the progression of rutting. Significant
rutting developed in the low void mixes. The results suggested that removal be considered for mixtures with air voids below 2.75% but
that no pay adjustment was necessary for air voids above this level. However, the NCAT results were limited to one pavement structure,
one set of materials, one climate and low voids in the surface mix only. In the APT, low air void mixtures were placed in either the
surface or the intermediate course and different materials were used. The pavement response (permanent deformation of the top
pavement layers) resulting from repetitive APT wheel passes was measured using a laser based system. Lastly, a simplified mechanistic
analysis, using a software program called QRSS (Quality Related Specification Software) was used in an attempt to simulate the effects of
low void mixtures on pavement performance and service life with different materials in different pavement layers and under different
traffic loads. The results of these efforts were used along with engineering judgment to formulate the desired decision‐support tool.
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