In order to avoid the occurrence of early-age damage, cement-treated base (CTB) materials must be allowed to cure for a period of time before the pavement can be opened to traffic. The purpose of this research was to evaluate the utility of the soil stiffness gauge (SSG), heavy Clegg impact soil tester (CIST), portable falling-weight deflectometer (PFWD), dynamic cone penetrometer, and falling-weight deflectometer for assessing early-age strength gain of cement-stabilized materials. Experimentation was performed at four sites on a pavement reconstruction project along Interstate 84 near Morgan, Utah, and three sites along Highway 91 near Richmond, Utah; cement stabilization was used to construct CTB layers at both locations. Each site was stationed to facilitate repeated measurements at the same locations with different devices and at different curing times. Because of the considerable attention they have received in the pavement construction industry for routine quality control and quality assurance programs, the SSG, CIST, and PFWD were the primary focus of the research. Statistical techniques were utilized to evaluate the sensitivity to curing time, repeatability, and efficiency of these devices. In addition, the ruggedness and ease of use of each device were evaluated. The test results indicate that the CIST data were more sensitive to curing time than the SSG and PFWD data at the majority of the cement-treated sites during the first 72 hours after construction. Furthermore, the results indicate that the CIST is superior to the other instruments with respect to repeatability, efficiency, ruggedness, and ease of use. Because the CIST is less expensive than the SSG and PFWD, it is more likely to be purchased by pavement engineers and contractors involved with construction of CTBs. For these reasons, this research suggests that the CIST offers greater overall utility than the SSG or PFWD for monitoring early-age strength gain of CTB. Further research is needed to identify appropriate threshold CIST values at which CTB layers develop sufficient strength to resist permanent deformation or marring under different types of trafficking.

In order to avoid the occurrence of early-age damage, cement-treated base (CTB) materials must be allowed to cure for a period of time before the pavement can be opened to traffic. Trafficking of a CTB before sufficient strength gain has occurred can lead to marring or rutting of the treated layer. The specific objectives of this research were to examine the correlation between Clegg impact values (CIVs) determined using a heavy Clegg impact soil tester and rut depths measured in newly constructed CTB and subsequently establish a threshold CIV at which rutting should not occur.The experimental work included field testing at several locations along United States Highway 91 near Smithfield, Utah, and laboratory testing at the Brigham Young University (BYU) Highway Materials Laboratory. In both the field and laboratory test programs, ruts were created in CTB layers using a specially manufactured heavy wheeled rutting device (HWRD). In the field, ruts caused by repeated passes of a standard pickup and a water truck were also evaluated. The collected data were analyzed using regression to identify a threshold CIV above which the CTB should not be susceptible to unacceptable rutting. From the collected data, one may conclude that successive wheel passes each cause less incremental rutting than previous passes and that CTB similar to the material tested in this research should experience only negligible rutting at CIVs greater than about 35. The maximum rut depth measured in either field or laboratory rutting tests was less than 0.35 in. in this research, probably due to the high quality limestone base material utilized to construct the CTB. In identifying a recommended threshold CIV at which CTB layers may be opened to early trafficking, researchers proposed a maximum tolerable rut depth of 0.10 in. for this project, which corresponds to a CIV of approximately 25. Because a CIV of 25 is associated with an acceptably minimal rut depth even after 100 passes of the HWRD, is achievable within a reasonable amount of time under normal curing conditions, and is consistent with earlier research, this threshold is recommended as the minimum average value that must be attained by a given CTB construction section before it can be opened to early trafficking. Use of the proposed threshold CIV should then ensure satisfactory performance of the CTB under even heavy construction traffic to the extent that the material properties do not differ greatly from those of the CTB evaluated in this research.

A relatively new method used to reduce the amount of cement-treated base (CTB) shrinkage cracking is microcracking of the CTB shortly after construction. Three portable instruments used in this study for monitoring the microcracking process include the heavy Clegg impact soil tester (CIST), portable falling-weight deflectometer (PFWD), and soil stiffness gauge (SSG). The specific objectives of this research were 1) to evaluate the sensitivity of each of the three portable instruments to microcracking, and 2) to compare measurements of CTB stiffness reduction obtained using the three devices. The test locations included in this study were Redwood Drive and Dale Avenue in Salt Lake City, Utah; 300 South in Spanish Fork, Utah; and a private access road in Wyoming. Experimental testing in the field consisted of randomized stationing at each site; sampling the CTB immediately after the cement was mixed into the reclaimed base material; compacting specimens for laboratory testing; and testing the CTB immediately after construction, immediately before microcracking, immediately after each pass of the vibratory roller during the microcracking process, and, in some instances, three days after microcracking. Several linear regression analyses were performed after data were collected using the CIST, PFWD, and SSG during the microcracking process to meet the objectives of this research. Results from the statistical analyses designed to evaluate the sensitivity of each of the three portable instruments to microcracking indicate that the PFWD and SSG are sensitive to microcracking, while the CIST is insensitive to microcracking. Results from the statistical analyses designed to compare measurements of CTB stiffness reduction demonstrate that neither of the instrument correlations involving the CIST are statistically significant. Only the correlation between the PFWD and SSG was shown to be statistically significant. Given the results of this research, engineers and contractors should utilize the PFWD or SSG for monitoring microcracking of CTB layers. The heavy CIST is unsuitable for monitoring microcracking and should not be used. For deriving target CTB stiffness reductions measured using either the PFWD or SSG from specified targets measured using the other, engineers and contractors should utilize the correlation chart developed in this research.

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.