DETERMINATION OF THE CRITICAL THAW-WEAKENED PERIOD IN ASPHALT PAVEMENT STRUCTURES

Abstract

Preliminary results of a soil-temperature monitoring program beneath asphalt-surfaced forest roads in northwest Montana indicate that the critical spring thaw-weakened period of a pavement structure can, in most cases, be identified by temperature alone. At all monitored locations, thawing below the pavement did not commerce until the average soil temperature above a depth of 36 in., excluding the asphalt mat, had risen to approximately 30 deg. F. Initial subpavement thawing was indicated by temperatures above the freezing point of local soilwater as measured at the asphalt-base course interface. Pavement strength values were equal to or greater than those recorded the previous fall when the depth of thaw had progressed to approximately 48 in. below the asphalt mat in areas underlain by nonplastic soils. This relationship was less clear in plastic soils. Utilizing this soil-temperature monitoring program, road managers have the means to forewarn facility users of the possible imposition of vehicle load restrictions. This program provides accurate idenification of the onset of spring thaw weakening and allows an evaluation of the strength recovery as the critical period wanes.