Three different kinds of base material of varying base thicknesses were tested at the Washington State University Test Track on Ring #3 during the fall of 1967 and the spring of 1968. Twelve 18-foot test sections consisting of 4.5, 7.0, 9.5 and 12 inches of untreated crushed rock surfacing top course base; 3.0, 5.0, and 7.0 and 9.0 inches of emulsion treated crushed surfacing top course base; and 0.0, 2.0, 3.5 and 5.0 inches of special non-fractured screened aggregate asphalt treated base, covered by a uniform 3.0-inch thick Class "B" asphalt concrete wearing course were tested during this period. This pavement structure was built on a clay-silt subgrade soil.
Instrumentation consisted of moisture tensiometers, strain gages, pressure cells, LVDT gages and thermocouples for measuring moisture, strain, stress, dynamic deflections and temperatures. Benkleman beam readings were taken.
The testing period revealed that the fall failure modes were different from the spring failures. The fall failure pattern started from transverse cracks in the thin sections which developed into alligator cracking patterns. These cracks appeared after a period of cold weather and heavy rains followed by a warming period. It seems that thermal and mechanical loads were responsible for the fall failures on the thin sections. The spring failures were very rapid and sudden and were due to environmental factors which led to saturated subgrade, thus resulting in poor bearing capacity. Punching shear was the failure mode. The thickest sections survived without cracks but developed severe rutting. Examination revealed that these ruts extended into the subgrade and that fatigue cracking was developing on the bottom of the bases.
Comparison of the results with those obtained from Ring# 2, which was similar in base materials and thickness, show that they were similar in many respects. This indicates that the test track is capable of replicating results and is a reliable research instrument.
Equivalencies were developed for the different materials. On this basis the special aggregate asphalt treated base was superior to the emulsion treated and untreated crushed rock bases in that order. These results were comparable to those obtained from test Ring #2.
Maximum values for static and dynamic deflections, strains and stresses for different times and temperatures were developed. The lateral position of the dual tires with respect to the gage severely affected the strain, stresses and deflection values. Temperature also caused variations in the measurements.
Spring instrument readings for static and dynamic deflections, strain and stress show increased values by as much as 2 to 4 times of those obtained in the fall. Spring subgrade conditions probably are responsible for these differences.
Ring #3 series operational time was twice that of Ring #2 and sustained four times the wheel load applications. Construction and testing environmental conditions were superior to those for Ring #2 and hence contributed to the longer test period. This points out that environmental factors are very important in pavement life.
January 12, 2008
Milan Krukar, John C. Cook.
Washington State University. Highway Research Section.
- # of Pages: 156 p., 15,097 KB (PDF)
- Subject: Asphalt cement, Base course (Pavements), Benkelman beam, Circular test tracks, Cracking of asphalt concrete pavements, Deflection, Emulsions, Foundations, Gravel, Load cells, Pavement design, Pavement performance, Shear stress, Strain gages, Tensiometers, Wearing course (Pavements), Wheel loads.
- Keywords: Aggregate, alligator cracking, asphalt concrete, base materials, bearing capacity, Benkleman beam, concrete, dual tires, fatigue cracking, loads, pavement life, pressure, pressure cell, research, soil, strains, stresses, subgrade, temperature, test track. tire, Washington State University.
- Related Publications: Pavement Research at the Washington State University Test Track, Volume One, Experimental Ring No. 1: A Study of Cement Treated and Asphaltic Treated Bases, (WA-RD 15.1).
Pavement Research at the Washington State University Test Track. Volume Two, Experimental Ring No. 2: A Study of Untreated, Emulsion Treated, and Asphaltic-Cement Treated Bases, (WA-RD 15.2).
Pavement Research at the Washington State University Test Track. Volume 4, Experimental Ring No. 4: A Study of Untreated, Sand Asphalt, and Asphalt Concrete Bases, (WA-RD 15.4).
Pavement Research at the Washington State University Test Track. Volume 5, Evaluation and Analysis of Results from Experimental Rings No. 1-4, (WA-RD 15.5).
Pavement Research at the Washington State University Test Track. Volume 6, The Application of the WSU Test Track Data to Flexible Pavement Design, (WA-RD 15.6).
This abstract was last modified April 29, 2008