Abstract

The objective of this research was to compare the stiffness of cement-treated base (CTB) layers and untreated base course (UTBC) layers in a cold region through a typical year. The scope of work included testing of three residential pavement segments comprising CTB layers and two comparable pavement segments comprising UTBC layers in northern Utah. Design thicknesses were verified through drilling and dynamic cone penetrometer testing in September 2024. Following 3 to 15 years of service, the sites were evaluated using portable falling-weight deflectometer (PFWD) testing in May 2024, July 2024, September 2024, November 2024, January 2025, and March 2025. After modulus values for the pavement layers were determined from the PFWD test results, a mechanistic-empirical (M-E) pavement analysis was performed for each site for each month during which data were collected, and the numbers of allowable equivalent single-axle loads (ESALs) were computed. Based on the average modulus values for the sites computed for each month during which data were collected, the coefficient of variation (COV) for the CTB was 62.4%, while the COV for the UTBC was 107.2%, indicating that CTB layers have a lower seasonal variation in stiffness than UTBC layers. The average CTB modulus values were 173%, 336%, and 367% higher than the UTBC modulus values during the months of May, July, and September, respectively, and 54%, 23%, and 32% lower than the UTBC modulus values during the months of January, March, and November, respectively. Overall, the annual average CTB modulus was 27% higher than the annual average UTBC modulus in this study. M-E pavement analysis indicated that the allowable ESALs for the CTB sites were 60%, 887%, 548%, 1,219%, and 229% higher than the allowable ESALs for the UTBC sites during the months of March, May, July, September, and November, respectively, and 26% lower than the allowable ESALs for the UTBC sites during the month of January. The COV for the CTB sites was 54.4%, while the COV for the UTBC sites was 136.7%, indicating that the CTB sites have a lower seasonal variation in allowable traffic loading than UTBC sites. Overall, the annual allowable ESALs for the CTB sites was 46% higher than the annual allowable ESALs for the UTBC sites in this study. Given these findings, pavement engineers and managers in cold regions such as northern Utah should design pavement structures comprising CTB layers rather than UTBC layers when greater structural capacity, with less seasonal variation, is important.

Degree

College and Department

Ira A. Fulton College of Engineering; Civil and Environmental Engineering

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