THE STATE-OF-THE-PRACTICE IN WYOMING--PART I

This paper outlines state-of-the-practice in Wyoming with regard to protecting pavements from excessive moisture. In the arid climate of Wyoming, with deep-seated water table conditions, it is not an impossible attempt to catch surface water. The plant-mix wearing course is an open-graded asphalt mix, that when properly designed and constructed serves several important purposes: it provides an excellent skid-resistant surface, it provides an internal drainage system to remove surface water in a lateral direction, it provides a seal for the underlying surfacing materials, and it provides a quiet smooth-riding surface section. Wyoming's specifications require that 75% of the aggregate (by weight) retained on the #4 sieve have at least one fractured face and have a maximum wear-grading of 35. A special gradation on construction plans limits the percent passing the #8 sieve to a maximum of 25%. Asphalt mixes are evaluated by the Marshall stability method in conjunction with immersion-compression ratios. Wyoming's plant-mix contains 1.5-4% total air voids, but the plant-mix wearing course contains from 6% to at least 10% total air voids. Immersion-compression ratio gives the most valuable and reliable results when evaluating the effects of water in paving materials. The state's primary deterrent for water in pavement section is a plant-mix wearing course that is a highly asphalted mix. It is intended that the excess asphalt drain down and help to seal off the underlying paving materials. Wyoming's primary concern with regard to rigid pavements is to protect the subgrade soils from water intrusion, particularly swelling soils, with such things as drainage, asphalt membranes, and sealing shoulders.