Non-Nuclear Methods for Compaction Control of Unbound Materials (2014)

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5 chapter one INTRODUCTION INTRODUCTION AND BACKGROUND Compaction is defined as the process by which particles of soil and unbound aggregates, hereafter referred to as “unbound materials,” are rearranged and packed together into a denser state by applying mechanical energy. As unbound materials reach a denser state through compaction, their shear strength and stiffness are enhanced. This makes them capable of resist- ing more stress with less deformation and thus prevents or reduces the development of detrimental excessive settlement during service. In addition, compaction helps to decrease the susceptibility of the unbound materials to environmental changes, especially those caused by frost heave, swelling, or shrinkage (Holtz et al. 2010). Therefore, proper compaction of unbound materials is one of the most critical components in the construction of pavements, airfields, and embankments to ensure their adequate performance, durability, and stability over time. Compaction control is used to ensure that proper degree of densification is achieved. Appropriate control of the compaction process depends on compaction specifications. There are two main types of such specifications: (1) method or procedure specifications, and (2) end-product specifications. Both types have similarities in site preparation requirements and peripheral construction requirements, such as site drainage and runoff control, hours of work, and other contractual details. However, there are several differences between the two. With method or proce- dure specifications, the type, weight, and number of passes of compaction equipment, as well as the lift thicknesses (or maximum allowable material volume), are specified based on prior knowledge of the materials or field test sections. On the other hand, with end-product specifications, sometimes called performance specifications, the contractor is required to compact the soil layer to achieve a target density or stiff- ness value. As shown in Table 1, most state departments of transpor- tation (DOTs) currently employ end-product specifications for compaction control of unbound materials in pavement layers, subgrade, and embankments. DOTs assess the quality of compaction of those materials by comparing their field density measurements to a target dry density value. The target density value typically is determined by conducting a specified laboratory standard compaction test, such as the AASHTO T99 or AASHTO T180, on the same material com- pacted in the field. The nuclear density gauge (NDG) is the device used by most state DOTs for measuring the field den- sity of compacted layers of unbound materials (Tutumluer 2013). However, this device contains radioactive materials that can be hazardous to the operators’ health. Thus, its use entails extensive handling, storage, calibration, maintenance, and transportation regulations. All operators are required to undergo radiation safety training and know all applicable safety procedures and regulations. In addition, dosimeters (or film badges) are required to monitor the radiation when using the nuclear density device. Annual calibration and rou- tine safety procedures are also needed to maintain the gauges. Use of the NDG also requires strict licensing and relicens- ing, record keeping, and storage. The costs associated with owning, operating, licensing, transporting, and maintaining NDGs can be prohibitive. Table 2 provides a summary of those costs (Cho et al. 2011). In addition, improper disposal of NDGs has resulted in environmental contamination inci- dents costing, in some cases, several million dollars in cleanup (TransTech Systems, Inc. 2008). Because of the regulatory, safety, and economic burden associated with NDG use, as well as the Department of Homeland Security’s desire to reduce the amount of radio- active material in common use, several non-nuclear devices for density measurement have been proposed and evalu- ated during the past decade. These devices use electrical methods and are based on new technologies, such as time domain reflectometry (TDR) and dielectrics. Various agen- cies, including FHWA and state DOTs, have evaluated the devices in laboratory and field studies and compared their performance with that of the conventional NDG. Neverthe- less, the use of such devices has not been adopted or widely implemented by state DOTs. Although the compaction control density method widely practiced by state DOTs is simple and relatively straight- forward, it nonetheless presents a number of challenges for inspectors and designers. For example, the AASHTO T99 or AASHTO T180 test is limited in that it determines the required density of a variable material in only a very small sample. More compaction tests could be performed to increase the statistical confidence, but this approach is impractical because these tests are time consuming (Davich et al. 2006). In addition, the energy specified in the standard Proctor test method, first developed more than seven decades ago, does

6 TABLE 1 SUMMARY OF COMPACTION CONTROL SPECIFICATIONS OF STATE DOTs State Earthwork Specification Compaction Control Method Type Minimum Compaction Requirements Loose Lift Thickness Moisture Control Requirements Alternative Methods Alabama (2012) Specified density Embankment 95% RC (AASHTO T99: Method A for 10% passing or less; Method C for more than 10% retain on No. 4; Method D for 20% or more retained.) 8 in. (loose) Strict moisture control will not be required. N/A Modified or improved roadbed layer 100% RC (AASHTO T99: Method A for 10% passing or less; Method C for more than 10% retain on No. 4; Method D for 20% or more retained.) — OMC ± 2% Base Alaska (2004) Specified density Embankment 95% RC (AASHTO T180 and AASHTO T224) 8 in. (loose) OMC ± 2% Compact until embankment does not rut under the loaded hauling equipment Subgrade N/A Base 98% RC (AASHTO T180 and AASHTO T224) Arizona (2008) Specified density Embankment 100% of RC for top 6 in and beneath approach and anchor slabs, 95% RC for other (ADOT Material testing manual) 8 in. (loose) At or near OMC N/A Lime/cement treated subgrade 100% of RC (ADOT Material Testing Manual) 8 in. (loose) Base Arkansas (2003) Specified density All type 95% Relative density (AASHTO T99: Method A for 10% passing or less; Method C for more than 11–30% retain on #4; and AASHTO T180 Method D for more than 30% or more retained) 10 in. (loose) At OMC N/A Subgrade — Cement treated base 95% of RC (AASHTO T134) — ±5% of OMC California (2010) Specified density All types 95% RC (California Test 216 or 231) 8 in. (loose) Suitable moisture content such that required density can be obtained and N/A Where 95% RC not required 90% RC (California Test 216 or 231) Aggregate base/subbase 95% RC (California Test 216 or 231) embankment stable Colorado (2011) Specified density Embankment 100% RC (AASHTO T99) or 95% RC (AASHTO T180 8 in. (loose) OMC 2% (dry side) Proof rolling Lime treated subgrade 95% RC (AASHTO T99) ±2% of OMC — Aggregate base 95% RC (AASHTO T180) — — Connecticut (2004) Specified density Embankment 95% RC (AASHTO T180 Method D) 12 in. (loose) At OMC N/A Subgrade Processed aggregate base Delaware (2001) Specified density Embankment 95% RC (AASHTO T99 Method C, Modified) 8 in. (loose) ±2% of OMC N/A Subgrade Aggregate base 98% RC (AASHTO T99 Method C, Modified) District of Columbia (2009) Specified density Embankment 95% RC full depth and top 6 in. of subgrade (AASHTO T180 Method D) 6 in. (loose) Not specified N/A Subgrade 95% RC (AASHTO T180 Method D) Aggregate base 95% RC (AASHTO T180 Method D) Control strip Florida (2013) Specified density Embankment 100% RC (AASHTO T99 Method C) 12 to 6 in. (compacted) Suitable moisture content such that required density can be obtained N/A Subgrade 98% RC (AASHTO T180 Method C) 12 in. (compacted) Base 4 to 8 in. (compacted)

7 TABLE 1 (continued) (continued on next page) Hawaii (2005) Specified density Embankment 95% RC (AASHTO T180 Method D and T224) 9 in. (loose) ±2% of OMC N/A Subgrade N/A Base Idaho (2012) Specified density Embankment 95% RC (AASHTO T99 Method A or C) 8 in. (loose) +2/-4% of OMC N/A Subgrade Granular base Illinois (2012) Specified density Embankment Height < 1-1/2 ft 95% RC (AASHTO T99 Method C and T224) 8 in. (loose) Top 2 ft not more than 120% OMC such that adequate compaction is achieved. N/A 1-1/2 ft < height < 3 ft First lift 90% RC; remainder 90% RC (AASHTO T99 Method C and T224) Height > 3 ft Lower 1/3 of the embankment to 90% RC; first lift above lower 1/3 to 93% with remainder to 95% RC (AASHTO T99 Method C and T224) Specified density and DCP Subgrade 95% RC (AASHTO T99 Method C and T224) with IBV based on DCP = 8 (Illinois Test Procedure 501) N/A Specified density Granular base 100% RC (AASHTO T99 Method C and T224) 8 in. N/A Indiana (2012) Specified density or stiffness/ strength Embankment 95% RC (AASHTO T99 Method C and T224) DCP or LWD target value 8 in. (loose) -2% to +1% OMC Proof rolling -3% to 0% OMC for loessial soils Subgrade 100% RC (AASHTO T99 Method C and T224) or DCP target value Aggregate base 100% RC (AASHTO T99 Method C and T224) or LWD target value Iowa (2012) Specified density and DCP Embankment 95% RC (AASHTO T99 Method C) and DCP stability and uniformity limits Variable, such that adequate compaction is achieved Variable such that adequate compaction is achieved N/A Roller walkout Compacted a minimum of 1 pass per 1 in. of loose fill until the tamping feet penetrate 3 in. or less into an 8-in. lift Variable Variable Specified density Natural subgrade 95% RC (test method Iowa No. 103) — — Base Kansas (2007) Specified density Embankment As specified within construction plans 8 in. (loose) Specified on construction plans unless approved by engineer N/A Cement/fly ash treated subgrade 95% RC (AASHTO T99) OMC ± 3% Granular base 95% RC (AASHTO T99) OMC ± 3% Kentucky Specified density Embankment 95% RC (KM 64-511) 12 in./3ft OMC ± 2% N/A Subgrade Control strip Base 98% RC, single point 95% (KM 64-511) 8 in. — Louisiana (2006) Specified density Embankment 95% RC (DOTD TR415 or TR418) Nonplastic material 15 in. ±2% of OMC N/A Subgrade Base — State Earthwork Specification Compaction Control Method Type Minimum Compaction Requirements Loose Lift Thickness Moisture Control Requirements Alternative Methods Georgia (2010) Specified density Embankment Full depth and 100 ft from bridge edge: 100 RC (GDT 7) 8 in. At OMC N/A Full depth 95% RC; top 1 ft 100% (GDT 7) Subgrade 95% RC (GDT 7) Base

8 TABLE 1 (continued) Michigan (2012) Specified density Embankment Cohesive material 95% RC (Michigan Density Testing and Inspection Manual) 9 in. (loose) OMC to 4% OMC Twelve-inch layer method Granular material 15 in. (loose) OMC to 5% OMC Minnesota (2005) Specified density or stiffness/ strength Embankment Upper 3 ft of embankment or portions adjacent to structures 100% RC (Minnesota Grading and Base Manual) DCP or LWD target limit 8 in. (loose) 65%–102% OMC Quality compaction method; DCP for granular material Below upper 3 ft and not adjacent to structures 95% RC (Minnesota Grading and Base Manual) DCP or LWD target limit 12 in. 65%–115% OMC Subgrade 100% RC (Minnesota Grading and Base Manual) DCP or LWD target limit Base 65% of OMC to OMC Missouri (2013) Specified density Embankment Embankments more than 50 ft below the top of finished subgrade, within 100 ft of structures, or within 18 in. of subgrade 95% Relative Compaction (AASHTO T99, Method C) 8 in. (loose) Such that adequate compaction is achieved DCP index for Type 7 base All other embankments unless otherwise noted 90% Relative Compaction (AASHTO T99, Method C) 0% to +3% OMC for loessial soils Subgrade 95% RC (AASHTO T99, Method C) MC for adequate compaction is achieved Aggregate Base 95% (AASHTO T99, Method C) Mississippi (2004) Specified density Embankment 95% to 98% of maximum density 8 in. (loose) Such that adequate compaction is achieved N/A Base Average of five at least 93% of maximum density, no single density below 89% of maximum density Montana (2006) Specified density Earth embankment B including all backfills 90% of maximum density (AASHTO T99) 8 in. (loose) ±2% of OMC N/A Subgrade 95% of maximum density (AASHTO T99) Aggregate base 98% of maximum density (MT-230) Nebraska (2007) Specified density Embankment 95% RC (NDR T99) 8 in. (loose) N/A Stabilized subgrade 100% RC (NDR T99) Base — Nevada (2001) Specified density 5 ft or less in height 90% RC (test method Nevada No. T101) 8 in. (loose) Not specified N/A All other (including subgrade and aggregate base) 95% RC (test method Nev. No. T101) Maine (2002) Specified density Embankment 90% of max density (AASHTO T180, Method C or D) 8 in. (loose) Proper to maintain compaction and stability N/A Subgrade — Aggregate base and subbase 95% RC (AASHTO T180, Method C or D) — Maryland (2008) Specified density Embankment 1 ft below top of subgrade 92%; top 1 ft 97% (AASHTO T180) 8 in. (loose) ±2% of OMC N/A Subgrade 97% RC (AASHTO T180) Base 97% (AASHTO T180) Massachusetts (2012) Specified density Embankment 95% Relative density (other than rock) (AASHTO T99, Method C) 12 in. (loose) at OMC N/A Subgrade 95% RC (AASHTO T99, Method C) Gravel base State Earthwork Specification Compaction Control Method Type Minimum Compaction Requirements Loose Lift Thickness Moisture Control Requirements Alternative Methods

9 (continued on next page) TABLE 1 (continued) New York (2008) Specified density Embankment 90% minimum; 95% minimum for subgrade of embankment (AASHTO T99) Depends on compaction device Not specified N/A Subgrade Soil cement base 95% of maximum density (AASHTO T99) North Carolina (2012) Specified density Embankment 95% RC [AASHTO T99 (state modified)] 10 in. (loose) Not specified Proof rolling Subgrade 100% RC [AASHTO T180 (state modified)] 8 in. Base Aggregate base 100% RC [AASHTO T99 (state modified)] N/A Cement treated 97% RC [AASHTO T99 (state modified)] +1.5% of OMC Lime treated 97% RC [AASHTO T99 (state modified)] + 2% of OMC North Dakota (2008) Specified density Embankment 95% RC (AASHTO T99) / 90% (AASHTO T180) 12 in. (loose) -4% of OMC to +5% of OMC (AASHTO T99) / OMC to +5% of OMC (AASHTO T180) N/A Subgrade — Specification method Base — — — — Ohio (2013) Specified density Embankment γmax (pcf) % RC 8 in. (loose) Suitable moisture content N/A 90 to 104.9 102 105 to 119.9 100 120 and more 98 Subgrade AASHTO T99, T272 and supplemental specification 1015) Test strip Aggregate base 98% RC of test section ±2% of OMC Oklahoma (2009) Specified density Embankment 95% RC (AASHTO T99 Methods C or D) 8 in. (loose) ±2% of OMC N/A Subgrade Aggregate base 98% (Type A); 95% for Types B, C, and D Oregon (2008) Specified density or Deflection Embankment 95% RC (AASHTO T99) 8 in. (loose) -4% of OMC to OMC +2% Proof rolling using ODOT TM 158 Subgrade — Aggregate base 100% RC Rhode Island (2010) Specified density Top 3 ft of embankment 90% RC (AASHTO T180 and T224) 12 in. (loose) Not specified N/A Reminder up to subgrade and subgrade 95% RC (AASHTO T180 and T224) Aggregate base 95% RC (AASHTO T180 and T224) New Hampshire (2010) Specified density Embankment 98% RC (beneath approach slab and 10 ft back of a structure); all other 95% (AASHTO T99) 12 in. (loose) Not specified N/A Subgrade 95% Relative density (AASHTO T99 or control strip) Base 8 in. New Mexico (2007) Specific density Embankment 95% Relative density (AASHTO T99 Method C) 8 in. (loose) OMC to OMC –5%; for soil with PI > 15 OMC to OMC +4% N/A Subgrade Top 6 in. 100%; soil with PI³15: 95% (AASHTO T99, Method C) Base 95% of maximum density (AASHTO T180) 6 in. New Jersey (2007) Specified density Embankment 95% Relative density (AASHTO T99, Method C) 12 in. (compacted) Not specified End dumping method, control fill method, direct method Subgrade Proof rolling for subgrade Control strip Base Q³ 0.36 (where Q = (Average lot density– 0.95 * Maximum Density)/Range of Lot Density State Earthwork Specification Compaction Control Method Type Minimum Compaction Requirements Loose Lift Thickness Moisture Control Requirements Alternative Methods

10 TABLE 1 (continued) Texas (2004) Specified density Embankment PI 15 = > density 98%; 15 < PI 35 => density 98% and 102% ; W Wopt PI > 35 => density 95% Da and 100% Da; W Wopt. (Tex-114-E) 16 in. (loose) 15 < PI 35 => D W Wopt PI > 35 => W Wopt N/A Subgrade Lime treated or fly ash treated: 95% of maximum density (Tex-114-E); Lime treated 98% of maximum density (Tex-114-E) Utah (2012) Specified density Embankment Average per lot 96% (minimum), single determination 92% (minimum) (AASHTO T180 Method D for A-1 soils; AASHTO T99 Method D for all other soils) 12 in. (loose), may be reduced if unsatisfactory density Appropriate moisture N/A Untreated base course Average 97% RC (minimum); single point 94% RC (AASHTO T180 Method D for A- 1 soils; AASHTO T99 Method D for all other soils) OMC ± 2% Vermont (2006) Specified density Embankment Top 24 in. immediately above subgrade 95%; rest 90% relative density (AASHTO T99, Method C) 8 in. (loose) OMC + 2% N/A Subgrade 95% of maximum density (AASHTO T99, Method C) Subbase and base 95% RC (AASHTO T180, Method D) Not specified Virginia (2007) Specified density Embankment 95% RC 8 in. loose ±2% of OMC ±2% of OMC N/A Subgrade % Retained No. 4 RC 0–50 51–60 100 95 Base 61–70 90 Control strip Washington (2012) Specified density Embankment Method A: Not specified 8 in. Method A: suitable moisture content Method B: +3% of OMC; Method C: ±3% of OMC N/A Method B: 95% RC; height < 2 ft 90% RC Method C: 95% RC Subgrade 95% RC (% retained on No. 4: if 30 maximum (AASHTO T99 Method A); if more than 30% on # and 30% or less retained on 3/4 sieve (T180 Method D); if 30% or more on 3/4 sieve (WSDOT Method No. 606) 6 in. Aggregate base West Virginia (2010) Specified density Embankment 95% RC (WV specifications: MP 717.04.21, MP 207.07.20, MP 700.004.2, etc.) 12 in. (loose) (40% or higher passing 3/4 in. sieve) -4% of OMC to +3% of OMC (40% passing 3/4 in. sieve), OMC (elastic soils) N/A Subgrade and base South Carolina (2007) Specified density Embankment 95% RC (SC-T-29) 8 in. Suitable moisture content N/A Subgrade Base 100% RC (SC-T-29) ±2% of OMC South Dakota (2004) Specified density Embankment 95% or greater (AASHTO T99) 8 in. (loose) For OMC 0– 15% = > OMC -4% to OMC +4%; for OMC > 15% => OMC -4% to OMC +6% Ordinary compaction method Subbase and base Base 97% RC; subbase 95% (D 104, Method 4 and SD 105 or SD 114) Not specified N/A Tennessee (2006) Specified density Embankment 95% RC (AASHTO T99 and T224) 10 in. (loose) ± 3% of OMC N/A Base Aggregate base: 100% RC, 92 (single, minimum) (AASHTO T99 and T224) Subgrade (lime treated) Average per lot 96% (minimum), single determination 92% (minimum) (AASHTO T99 and T224) ±3% of OMC State Earthwork Specification Compaction Control Method Type Minimum Compaction Requirements Loose Lift Thickness Moisture Control Requirements Alternative Methods

11 design and compaction quality control processes. To address this problem, federal and state transportation agencies have investigated the use of compaction control procedures for unbound materials that are based on a criterion that closely correlates to the performance parameters used in the design, such as stiffness and strength. This effort was also motivated by the development and implementation of the Mechanistic– Empirical Pavement Design Guide (MEPDG). Currently, sev- eral in situ test devices are reported to measure the stiffness or strength properties of compacted unbound materials and are robust and accessible to different construction sites. These include the Briaud compaction device (BCD), Clegg ham- mer (CH), dynamic cone penetrometer (DCP), GeoGauge, light weight deflectometer (LWD), soil compaction super- visor (SCS), and portable seismic property analyzer (PSPA). not accurately represent the compaction energy levels cur- rently applied in the field (Davich et al. 2006). Other problems with the current density-based compac- tion control method arise from the design and performance perspective. Although compaction of unbound materials results in increased density, the main purpose of compac- tion is to improve the materials’ engineering properties, not only their density. The key functional properties of unbound layers are their stiffness and strength, which are measures directly related to their structural performance. Stiffness or strength parameters of unbound materials typically are used in the design of different transportation structures, such as pavements, but are not evaluated during the compaction process. Consequently, there is a missing link between the Wisconsin (2013) Specified density Embankment Embankments less than or equal to 6 ft or within 200 ft of a bridge abutment 95% RC (AASHTO T99, Method C) 8 in. (loose) Such that the material does not rut excessively and such that the material can be compacted properly N/A Embankments higher than 6 ft 6 ft below subgrade: 90% RC; within 6 ft from top: 95% RC (AASHTO T99, Method C) Subgrade Final 6 in. 95% RC (AASHTO T99, Method C) Wyoming (2010) Specified density Embankment 95% RC (Materials Testing Manual WY DOT and AASHTO T180) 8 in. (loose) -4% of OMC to +2% of OMC N/A Subgrade Base RC = relative compaction; OMC = optimum moisture content; γmax: = maximum dry density, N/A = not available. State Earthwork Specification Compaction Control Method Type Minimum Compaction Requirements Loose Lift Thickness Moisture Control Requirements Alternative Methods TABLE 1 (continued) TABLE 2 COSTS ASSOCIATED WITH OWNING AND OPERATING A NUCLEAR DENSITY GAUGE Item Cost Cost of nuclear gauge $6,950 Radiation safety and certification class $750 Safety training $179 Hazardous materials certification $99 RSO training $395 TLD Badge Monitoring $140/year Life of source capsule integrity 15 year Maintenance and recalibration $500/year Leak test $15 Shipping $120 Radioactive materials license $1,600 License renewal $1500/year Reciprocity $750 Source: Cho et al. 2011.

12 mented by state DOTs for compaction control to unbound materials. Finally, it highlights gaps in knowledge and cur- rent practices, along with research recommendations to address these gaps. STUDY APPROACH Various methods were used to collect information in this synthesis. They include a comprehensive literature review, a survey of materials/geotechnical engineers from state DOTs, and selected interviews. The following sections describe those methods. Survey Questionnaire A survey questionnaire was prepared and distributed to the materials/geotechnical engineers from all state DOTs and the Ontario Ministry of Transportation in Canada. The ques- tionnaire was designed to be both comprehensive and brief in an attempt to increase response rate. More details about the steps followed in conducting this survey are provided in chapter two. Literature Review A comprehensive literature review of all published national and international materials and ongoing research proj- ects focusing on the performance of various non-nuclear devices and methods used for compaction control of different un bound materials used in pavements, embankments, and foundations was conducted. The literature search included standard methods, such as TRB’s Transportation Research Information System (TRIS), COPENDEX, National Techni- cal Information Service (NTIS), as well as consulting with domestic and national experts in the field. Research reports on studies conducted by the FHWA, U.S. Army Corps of Engineers, and state DOTs on non-nuclear methods and devices for compaction control were reviewed. In addition, information was obtained from the state DOTs construc- tion specification books and manuals. The literature review results are presented in chapters three through five of the synthesis report. Interviews Interviews were performed over the phone and by e-mail with selected survey respondents to seek additional details about their experience with using non-nuclear methods for compaction control of unbound materials and clarify any discrepancies found in the questionnaire. In addition, those interviews have helped in developing the case examples for the implementation of stiffness- and strength-based specifications for compaction control of unbound materials in some states. Those are presented in chapter five of this report. At present, few state DOTs have included these devices in their specifications for compaction control of unbound mate- rials or have implemented their use in field projects. A national synthesis of previous research is needed to evaluate and compare the performance of various available non-nuclear methods and devices that can be used in com- paction control of unbound materials. This will allow state DOTs to understand the different non-nuclear methods that exist and know their advantages and limitations, which will help in implementing those methods and devices. This report synthesizes useful knowledge and information from a vari- ety of sources on the national and international experience in using non-nuclear methods for compaction control of unbound materials. The information collected by this syn- thesis includes the following: • 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 consideration, including pro- posed specifications; • The various types of non-nuclear devices available and comparisons with nuclear devices; • Comparison of measurements of non-nuclear device results to material properties (e.g., density, modulus, stiffness, moisture); • Issues with non-nuclear devices, such as accuracy, pre- cision, ease of use, reliability of data, safety, test time, level of expertise required, Global Positioning System (GPS) compatibility, calibration, durability, costs, and compatibility with various unbounded materials; and • Advantages, disadvantages, and limitations of the various compaction control devices. STUDY OBJECTIVES AND SCOPE The main objective of this synthesis is to compile and sum- marize all available information on the various non-nuclear devices and methods that have been used for compaction control of unbound materials. The synthesis focuses on non- nuclear devices that measure density, as well as those that evaluate in situ stiffness- and strength-related properties of unbound materials that can be used to examine the quality of construction. Information on the accuracy, repeatability, ease of use, test time, cost, GPS compatibility, calibration, compatibility with the various unbound materials, and depth of influence of the different non-nuclear compaction control devices is documented and discussed. In addition, the main advantages, disadvantages, and limitations of those devices are identified. All correlations between the measurements of the considered devices and density, as well as the resil- ient modulus or any other input parameter for designing transportation and geotechnical structures, are provided. The synthesis presents a review of stiffness- and strength- based specifications that have been developed and imple-

13 and provides a summary of the finding of studies that were conducted to evaluate them. Chapter four provides a descrip- tion of various in situ test methods that measure stiffness or strength properties and have been used in compaction control of unbound materials. In addition, it summarizes the findings of the studies conducted to evaluate those devices and high- lights the main advantages and limitations of those devices. Chapter five presents a review of stiffness- and strength-based compaction control specifications that have been developed or are being developed by state DOTs. Finally, chapter six summarizes the key findings and main conclusions from the literature and survey information compiled in chapters two through five. It also provides recommendations for future study and additional research needs. REPORT ORGANIZATION This report is organized into six chapters. Chapter two pre- sents the description, the respondents’ information, and the results of the survey questionnaire conducted as part of this synthesis. This information is included in chapter two before other chapters primarily to provide an overview of current state DOTs’ practices for compaction control of unbound materials and to give a picture of how state DOT engineers perceive the available non-nuclear compaction control devices. Chapter three discusses current state DOT specifications and practices for compaction control of various unbound materials that are based on density measurement. In addition, this chapter describes the various available non-nuclear density devices