The objectives of this research were 1) to examine correlations between compositional and structural properties of emulsion-treated base (ETB) layers, determine which of these factors exhibit the greatest spatial variability, and determine if significant differences exist between different test sections on a given project and 2) to investigate temporal trends in the structural properties of base materials treated with asphalt emulsion and to assess the rate at which ETB design properties are achieved. The research conducted in this study focused on testing of the ETB layer constructed on 7800 South (SR-48) in West Jordan, Utah. The research conducted in this study involved field and laboratory evaluations of spatial and temporal variability in properties of ETB. Regarding spatial results, the average modulus values of the ETB layer were unusually low for a typical stabilized base material and were in general even lower than the subgrade modulus values at this test site. All three sections had high moisture contents after compaction, with the moisture content of the ETB layer exceeding the specified optimum moisture content at many locations even before the emulsion was injected. One of the three test sections had higher percentages of reclaimed asphalt pavement and emulsion than the other two. The ETB compressive strength was very low throughout the entire year of testing, clearly demonstrating the consequences of inadequate emulsion curing associated with this project. The statistical analyses showed that higher pre-treatment moisture contents and higher amounts of binder added were associated with lower stiffness and strength, while higher wet densities were associated with higher stiffness and strength. The analyses also showed substantial variation in most response variables but comparatively low variation in predictor variables. Only four structural properties were significantly different between sections. Temporal testing was performed to monitor the properties of the ETB layer and to compare the ETB section to an adjacent untreated base course (UTBC) section. The ETB moisture content did not change significantly during the 1-year monitoring period, showing that drying of the ETB layer did not occur following placement of the hot mix asphalt surface. Furthermore, the analyses provided no evidence that the ETB layer experienced any sustained increase in strength as a result of emulsion curing; instead, the ETB modulus was shown to be greatly dependent on season, with higher ETB moisture contents and temperatures corresponding to lower ETB modulus values. Even during the winter when the ETB stiffness reached its peak, the modulus was still below the target value specified for this project. The statistical analyses indicated that the modulus values of the ETB and UTBC layers were not statistically different.

The objective of this research was to investigate emulsion-treated base (ETB) frost susceptibility in terms of both freeze-thaw cycling and frost heave. The research performed in this study involved laboratory testing of ETB materials sampled from both the Redwood Road and 7800 South reconstruction projects in northern Utah. The effects of freeze-thaw cycling were evaluated by comparing the stiffness and strength of tested specimens to the same properties of control specimens not subjected to freeze-thaw cycling. Frost heave testing enabled evaluation of the effects of emulsion content and degree of curing on the volumetric stability of ETB materials during sustained freezing. Since permeability affects the frost susceptibility of a material, samples were also prepared to specifically evaluate the effect of curing condition on the permeability of the two base materials when treated with emulsion. The results of freeze-thaw testing showed that both the Redwood Road and 7800 South specimens experienced decreases in modulus as a result of freeze-thaw damage. The results also showed that the Redwood Road specimens experienced substantial decreases in strength as a result of freeze-thaw damage. The specimens from 7800 South did not exhibit such strength loss; since those specimens initially had much lower modulus and unconfined compressive strength values than the Redwood Road specimens, they were less susceptible to stiffness and strength loss during the freeze-thaw test. Results for the frost heave tests showed that the untreated base materials were not susceptible to frost heave and that the addition of emulsion, with or without curing, did not change the frost heave behavior in a practically important way. While susceptibility to frost heave is not expected to be a problem with these base materials, the laboratory results revealed a significant increase in the permeability of the ETB specimens after curing, which could facilitate greater freeze-thaw damage. In consideration of these research results, engineers should ensure proper material sampling and laboratory testing to assess the efficacy of emulsion treatment for a given project. ETB to be constructed in cold regions should be subjected to freeze-thaw testing during the design phase, and designers should be aware that curing of the ETB may dramatically increase permeability and therefore increase frost susceptibility.

The first objective of this research was to investigate temporal trends in the mechanical properties of base materials stabilized with asphalt emulsion and to assess the rate at which emulsion-treated base (ETB) design properties are achieved. The second objective of this research was to identify construction and environmental factors most correlated to specific mechanical properties of ETB layers and to determine which construction factors exhibit the greatest variability. Additional statistical analysis was performed to determine if significant differences existed between different test sections on a given project. In this research, three experimental sections were established along a pavement reconstruction project near Saratoga Springs, Utah. Field tests were performed to assess the structural properties of the ETB immediately following construction and at 2, 3, 7, and 14 days; 4 months; and 1 year. Measured values were plotted against time to determine trends in ETB strength development. Several statistical analyses were then performed on the collected data. Modulus values were consistently low in all three sections during the first two weeks of testing, increased dramatically by 4 months, and then decreased considerably by 1 year. During the first two weeks following construction, the average ETB structural coefficient was 0.04. Only two of the three sections reached the design structural coefficient of 0.25, which occurred after approximately 3 months; however, the average structural coefficient measured for all three sections after 1 year of curing, which included a winter, was only 47 percent of the design strength. The results of this research show that, while pavement capacity is sufficient at 4 months, it is severely reduced during the first two weeks and at 1 year. Trafficking under these reduced capacities is not recommended. Statistical analysis showed that gradation, binder change during emulsion treatment, and moisture content have the most significant impact on ETB structural properties. Gradation and binder change during emulsion treatment also exhibited significant variability; tighter specifications on material gradations and improved uniformity in emulsion distribution should therefore be considered. Because of the negative impacts of moisture on ETB strength development, construction should not be performed in conditions of excess moisture.