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A 5-year study of newly constructed pavements showed that a reduction in in situ air voids occurred both within and between wheelpaths for highways with an average daily traffic (ADT) load of less than 10,000 vehicles. Regardless of the level of voids immediately after construction, mixtures in the upper 65 mm (2.5 in.) within the wheelpath indicated a reduction in voids by 3 to 5 percent (e.g., from 10 to 6 percent voids), and by between 2 to 4 percent between the wheelpaths. Because only limited densification occurred below this depth for lower–traffic-volume facilities, reducing the mix design level of air voids from 4 percent to 2 percent for the lower lifts was suggested so that lower initial voids could be obtained during construction. An evaluation of older pavements indicated that moisture damage to the lower pavement layers was typical; thus, a change in mix design procedures might also help improve durability by increasing the film thickness. Pavements with high traffic volumes (>50,000 ADT) consistently indicated an increase in voids over time in the upper lift [40 mm (1.5 in.)], little change in the middle 65 mm (2.5 in.), and a decrease in the bottom 65 mm (2.5 in.). The hypothesis suggested to explain these findings was that a loss of material in the upper lifts was occurring, most probably due to moisture damage as the upper, more permeable wear course, commonly used in Minnesota, allowed water trapping at the wear and binder course (i.e., less permeable) interface. A further investigation of in situ void changes on an interstate indicated that for a pavement constructed with the same fine gradation in all lifts, traffic compacted the mixtures in a manner similar to that in low-volume roads. When the initial in situ voids increased from around 7 percent to nearly 10 percent, the influence of traffic on the densification was substantially increased. Content Note: This is the author’s version of a work that was accepted for publication in the Transportation Research Record: Journal of the Transportation Research Board, Issue Number: 1575, Publisher: Transportation Research Board ISSN: 0361-1981. The final version can be found at https://doi.org/10.3141/1575-01.

The objective of this investigation was to evaluate the use of a reduced structure thickness for the passing lane, (left lane) on four lane roadways. The design lane, right lane, on these roadways is estimated to carry between 81 and 97 percent of the total one way traffic load. In this report ASAL, Accumulated Standard Axle Load, will be used to replace the term Sigma N18. Present practice is to construct both right and left lanes to the same thicknesses. This results in an overdesign of the left lane.

A number of flexible pavement sections were constructed using limestone aggregate as the base material. As controls for comparison, identical sections were built using gravel base material. Evaluation was based primarily on Benkelman beam deflections. The results indicate that there is not any significant difference in the granular equivalency of the two aggregate types

This report evaluates the effect of cracking, breaking, or shattering PCC pavements before overlay as a means of reducing the amount and severity of reflected cracking. This investigation was expanded from Special Study No. 375, "Evaluation of Variable Thickness of Bituminous Overlay on Cracked PCC Pavement." A report on this study was issued in 1981.

Six methods of floating roadway widening sections over a peat swamp were designed and constructed on a two-lane roadway in 1976. The project location was on T.H. 53 between International Falls and Ray. Peat depths ranged from 8 to 15 feet. The investigation to date has shown that widenings can be floated on peat when fill height and loading rates are controlled. Performance of the sections will be monitored for a period of at least three years.

Several methods of floating widening sections over a peat swamp were designed and constructed on a two-lane roadway in northern Minnesota in 1976. These included the use of corduroy, wood chips and fabric. The study concluded that widening sections can be successfully and economically floated across peat swamps.