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SUMMARY Proper compaction of unbound materials is one of the most critical components in the con- struction of pavements, airfields, and embankments to ensure their adequate performance, durability, and stability. Currently, field density is used as an indicator to assess the quality of compaction and construction of those structures. The nuclear density gauge is the main device used for measuring the field density of compacted layers of unbound materials. How- ever, the use of this device entails extensive regulations and prohibitive costs associated with its handling, storage, calibration, and maintenance and the transportation of radioactive materials. Although the commonly used density-based quality control specifications are rela- tively straightforward and practical, they do not reflect the engineering properties of unbound materials required to ensure the materialsâ optimal performance and stability. In addition, the design of pavements and embankments is based on stiffness, strength parameters, or both. Thus, there is a missing link between the design process and construction quality control practices of unbound materials. To address this problem and help speed the construction pro- cess, as well as reduce costly construction oversight, federal and state transportation agencies have investigated the use of compaction control specifications for unbound materials that are based on a criterion that closely correlates to the performance measurements used in the design, such as stiffness and strength. Different non-nuclear devices have been proposed and evaluated during the past years. Although some of the devices measure density and moisture content, others assess the in situ stiffness- and strength-related parameters of various unbound materials. Several studies have evaluated the performance of these devices to compare and correlate their results with those obtained using the conventional nuclear density gauge. Nevertheless, non-nuclear devices have not been adopted or widely implemented by state departments of transportation (DOTs). This report synthesizes useful knowledge and information from a variety of sources on national and international experiences and practices using non-nuclear devices and methods for compaction control of unbound materials. The information collected by this synthesis includes: ⢠Types of compaction control testing devices used by state DOTs, including construction specifications; ⢠Non-nuclear devices that have been evaluated by state DOTs and those under consider- ation, including proposed specifications; ⢠Various types of non-nuclear devices available and comparison of these devices with nuclear devices; ⢠Correlation of non-nuclear device measurement results to material properties (e.g., den- sity, modulus, stiffness, moisture content); ⢠Issues with non-nuclear devices, such as accuracy, precision, ease of use, reliability of data, safety, test time, level of expertise required, Global Positioning System compatibil- ity, calibration, durability, costs, and compatibility with various unbound materials; and ⢠The advantages, disadvantages, and limitations of the various compaction control devices. Information in this synthesis was collected through a comprehensive literature review, surveys of U.S. DOTs and Canadian provincial transportation agencies, as well as interviews NON-NUCLEAR METHODS FOR COMPACTION CONTROL OF UNBOUND MATERIALS
2 with select state DOTs. A total of 41 transportation agencies (40 state DOTs and the Ontario Ministry of Transportation) responded to the survey questionnaire, which corresponds to a response rate of 80.4%. The main findings of the studies conducted to assess various non- nuclear devices are summarized in this report and used to compare their performance and identify their advantages and limitations. In addition, current DOT practices and procedures for compaction control of unbound materials are reviewed and documented. Finally, gaps in knowledge and current practices along with research recommendations to address these gaps are highlighted. Analysis of survey responses indicated that the majority of DOTs are using field density and/or moisture content measurements obtained by the nuclear density gauge for compaction control of various types of unbound materials. However, the DOTs are interested in hav- ing a non-nuclear device that could replace the nuclear density gauge and could be used in compaction control of unbound materials. Some DOTs have evaluated non-nuclear density devices, including the electrical density gauge, the time domain reflectometry-based mois- ture density indicator, and the soil density gauge. The results of the literature review indicate that the non-nuclear density devices have some advantages over the nuclear density gauge, such as not requiring special licensing to operate them; however, these devices were found to be more difficult to use and require longer testing time. This may explain the consensus among survey respondents on not recommending the use of any of the available non-nuclear density devices. There are several non-nuclear devices that have been used to measure the in situ moisture content of unbound materials; however, limited studies have been conducted to evaluate most of these devices. The speedy moisture tester and field microwave are the most com- mon non-nuclear devices used to measure the in situ moisture content of unbound materials. According to the survey conducted in this study, 13 states have recommended their use but four did not. The main limitation of both devices is that they cannot be used for all types of unbound materials. The speedy moisture tester cannot be used for highly plastic clayey soil or coarse-grained granular soil. Furthermore, the field microwave is suitable only for materials consisting of particles smaller than 4.75 mm (0.19 in.). Several DOTs have also assessed the performance of various in situ devices that measure stiffness/strength and can be used for compaction control of unbound materials. The evalu- ated in situ devices include Briaud compaction device (BCD), dynamic cone penetrometer (DCP), the Clegg hammer, GeoGauge, the light weight deflectometer (LWD), and the por- table seismic property analyzer (PSPA). Among these devices, the DCP, GeoGauge, and LWD were the most evaluated by DOTs. The DCP and LWD have been implemented by some DOTs for compaction control of unbound materials. Previous studies indicated that all devices except the PSPA might have difficulties in establishing target field value in the labo- ratory because of boundary effects on their measurement accuracy. Therefore, several DOTs have attempted to establish those values based on pilot projects or by constructing control strips along a project. Some devices also have limitations on the type of unbound materi- als they can test. In addition, those devices apply different load magnitudes during the test, resulting in different measurement results. Although the results of in situ stiffness/strength devices were found to be affected by moisture content, none of these devices have the abil- ity to measure it. The considered devices were reported to possess different influence depth. Thus, careful consideration should be given when analyzing their results and using them for compaction control. Several correlations were developed between the in situ test devicesâ measurements and design input parameters, such as the resilient modulus and California bearing ratio (CBR). However, those correlations are to be used with caution because they can be applied only to certain types of unbound materials and were developed for specified configurations of these devices. In general, no strong correlation was found between in situ stiffness/strength measurements and in-place density because their relationship continuously changes, depending on the moisture content.
3 According to the survey results, the majority of DOTs are interested in implementing stiffness- and strength-based specifications for compaction control of unbound materials, yet few DOTs have developed such specifications. This was attributed mainly to the lack of trained personnel and funds, the need for new testing equipment, and the unfamiliarity of contractors with such specifications. Only the Indiana and Minnesota DOTs have widely implemented stiffness- and strength-based specifications for compaction control using DCP and LWD measurements. Both states reported that they had positive experiences using the DCP as a tool for compaction control of unbound materials. Other states, such as Missouri, have used the DCP in compac- tion control but only for a specific type of unbound material.
