Impact of fines content on resilient modulus reduction of base courses during thawing

Abstract

"Resilient modulus (MR) of base course material is an important material input for pavement design. In Alaska, due to distinctiveness of local climate, material source, fines content and groundwater level, resilient properties of D-1 granular base course materials are significantly affected by seasonal changes. The presence of fines (P₂₀₀) affects frost susceptibility of base materials and controls the aggregates' ability to support vehicular load, especially during the spring-thaw period. To systematically evaluate the impact of fines content on the resilient properties of D-1 base course materials with varied fines content, gradation, moisture content and temperature during thawing and provide regression coefficients ki which are required for the flexible pavement design, a laboratory investigation was conducted on D-1 materials from Northern, Central, and Southeast Regions of Alaska Department of Transportation and Public Facilities (AKDOT & PF) at different temperatures, moisture and fines contents. MR data were determined by conducting repeated triaxial tests on D-1 materials with fines content ranging from 3.15% to 10% and moisture content from optimum moisture contents (OMC) -2% to OMC+0.7%, respectively. For MR tests at subfreezing temperatures, a frost heave cell was designed and fabricated for specimen preparation. To simulate the natural frost heave in winter, aggregate specimens experienced a freezing process by using frost heave cell. The designed frost heave cell is an open system which allowed free water intake during freezing process. Frost heave data and change of moisture contents after the freezing process were obtained from frost heave tests. Frost heave test results indicated that most of frost heave values were less than 3 mm for D-1 materials with fines contents ranging from 3.15% to 10%. The frost heave could be affected by initial moisture contents of aggregate specimens. MR tests results showed that MR decreased with an increase of moisture content. Within the scope of this study, impact of fines content varied which were affected by moisture contents of aggregate specimens. At subfreezing temperatures, there was a significant increase of MR when compared with room temperature. Impacts of fines and initial moisture content on MR values were weakened due to the change of moisture and aggregate structure after freezing process. Temperature was found to be an important factor influencing MR of D-1 materials, especially when temperature ranged from -5 °C to 0 °C. As temperature decreased, MR increased. However, when temperature was decreased to -5 °C, MR values seemed to be stable and further change of temperature did not result in any significant change of MR. Resilient properties of D-1 materials at room temperature after one freeze-thaw cycle were also investigated in this study. The reduction of MR after the freeze-thaw cycle was inevitable and significant, especially for aggregate specimens with high fines contents. Regression equations were also developed to correlate MR values with the physical properties (moisture and fines contents), stress states, and temperature conditions of D-1 materials. For D-1 materials tested in this study, at room temperature, MR was found to be a function of stress state, moisture and fines contents. At subfreezing temperatures, MR was a function of deviator stress, temperature, and aggregate type. These equations obtained can be used to predict MR values of Alaskan D-1 materials for pavement design"--Leaf iv