One of the major difficulties in asphalt concrete pavement construction is the control of materials and the subsequent level of payment to contractors for materials not conforming to specifications. The effect of this noncompliance on pavement serviceability is not fully established; however, it frequently results in reduced payments to contractors, which, in turn, causes much controversy between the two parties. Specific mixture properties outside specification tolerance, which are accepted by most agencies through reduced payment include percent compaction, asphalt content, and mix gradation. The reduced payment used normally relies heavily on the experience and judgment of the agencies; therefore, there is often wide disparity in the pay adjustment factors used.

The paper summarizes currently available techniques for estimating the modulus and fatigue life of asphalt mixtures and shows how these, together with existing failure criteria for fatigue and permanent deformation may be used to estimate the effects of changes in compaction on pavement life. Secondly, the results of extensive laboratory tests on asphalt mixtures from three projects in Oregon are reported. Tests were performed to evaluate the effect of mix variations (including density) on mix properties (modulus, fatigue life, and resistance to permanent deformation). Tests were run using both as-compacted and conditioned (vacuum saturated followed by freezing then heat soaking) specimens. The test used throughout was the ASTM Repeated Load Diametral Test (D 4123-82) modified slightly such that fatigue life could be evaluated.

The results of the test program indicated that percent compaction (or void content) was the most significant factor affecting mix performance. An increase in void content is associated with a decrease in modulus, fatigue life, and resistance to permanent deformation.

The result of the study findings was the development of new asphalt concrete compaction specifications for the state of Oregon. Not only does the Oregon Department of Transportation (DOT) now require a higher standard of compaction (91% of American Association of State Highway and Transportation Officials [AASHTO] T209 maximum specific gravity), but they have also spelled out clearly the penalties for not achieving density.