Evaluation of Surface Treatments

About the report:

This report describes the installation, evaluation, and performance of surface treatment test sections placed during 1983, 1984, and 1985. The study was initiated because of adhesion problems between asphalt and river gravel in the Fredericksburg District. However, observations by the researchers and complaints from other districts indicated that adhesion problems were also prevalent when crushed stone was used as the cover material. The study was continued through 1985 in order to include crushed stone. The results of this study indicate that the quality of a surface treatment is greatly influenced by the quantity of aggregate used, its cleanliness, the type and gradation of the aggregate, material adhesion, and construction techniques. It was found that some gravels perform better than others, but none perform as well as crushed stone. It was also learned that steel wheel rollers embed aggregate better than rubber tire rollers, but because of the irregular cross sections of so many secondary roads, the two should be used together. The recommendations in this report include the following: material quantities should be determined by a design method; adjustments should be made for road surface characteristics and traffic speeds and volumes; better construction techniques should be employed; river gravels should not be used on roads in traffic groups V and above; and, because of the problems caused by the wide tolerance in gradation on the No.4 screen of the No.8 aggregate used in surface treatments, the gradation should be changed to 12 percent + 12 percent passing the No.4 screen, 2 percent + 2 percent passing the No.8 screen, and 1 percent + 1 percent passing the No. 16 screen.

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