Specification Development

State DOT specifications contain the requirements for compaction control used in the acceptance decision process. These specifications can be either method or procedure, or end-product type specifications. Method or procedure specifications specify the type, weight, and number of passes of compaction equipment as well as the lift thickness or material volume. End-product specifications, often referred to as performance specifications, require the contractor to compact the soil layer to achieve a target value, typically a percentage of the maximum density

determined by a laboratory Proctor test.

9.1 Current Practice (Typical)

The NDG is the most commonly used device to ensure that the appropriate (minimum) in-place density is achieved. Densities—both laboratory and in-place—are functions of moisture content at the time of compaction. Most FDOT specifications do not include moisture content or a moisture content range. Field moisture measurement typically is determined by use of the speedy moisture tester, although base material moisture can be determined with the use of an approved NDG.

9.2 Modulus/Stiffness-Based Specification

Several requirements must be satisfied in order to transition from density-based specifications to modulus/stiffness-based specifications:

1. The proposed specification(s) shall be based on the field (in-place) measurement of modulus or provide a conversion to a modulus/stiffness value.

2. The type of device may be dependent on the type of material tested; e.g., +3/4 in. nominal maximum aggregate size (NMAS) or -3/4 in. NMAS.

3. In-place moisture content at the time of testing shall be determined.

4. Knowledge of in-place moduli would be beneficial if future design criteria are based on modulus values.

5. The specification(s) shall provide well defined methods applicable to the materials commonly encountered on FDOT construction projects.

6. Although the DCP does not measure stiffness/modulus, it is included as it could be used in conjunction with equipment that measures stiffness/modulus such as the LWD.

7. Although a particular device from a specific manufacturer cannot be specified,

consideration should be given to devices that are commercially available and represented by a sales and service network, preferably located in the United Sates, and have been determined acceptable based on this research.

8. Devices that have met the criteria to be included in the test methods published by the American Society for Testing Materials (ASTM) should be given greater consideration than devices without such methods.

9. To provide continuity validation, it is anticipated that a significant period of time be allocated for transition from the conventional moisture-density specifications to modulus-based specifications.

10. Field measurements shall be able to distinguish between acceptable and unacceptable states of compaction by being sensitive, accurate, and precise.

From our results, moduli from laboratory tests can differ significantly when compared to in situ results. These differences can be due to sampling disturbance, differences in the state-of-stress between the specimen and in-place material, long-term time effects, and inherent errors in the field and laboratory test procedures (Anderson and Woods, 1975).

9.2.1 Modulus/Stiffness-Based Design

The FDOT has not adopted the ME-PDG criteria for flexible pavement design. However, recent research, such as “Comparison of Resilient Modulus Values used in Pavement Design,”

recognized the need to equate moduli from in situ testing to laboratory modulus values. Although the focus of this research was the design of flexible pavement overlays, knowledge of in-place soil properties, such as modulus, would be of similar value for new construction design (Oh and Fernando, 2011).

During the 2014 site visit, Mn/DOT personnel stated that although in-place soil testing done with the LWD is based on deflection, modulus values also are reported for possible use in future designs.

The Maryland Department of Transportation State Highway Administration collected data to create a table of recommended moduli for unbound materials, “Catalog of Material Properties for Mechanistic-Empirical Pavement Design” (Schwartz and Li, 2011).

Table 9.1: Maryland DOT typical modulus values for design

Material Modulus (psi) Base/Subbase Materials Minimum Typical Maximum

Graded Aggregate Base 15,000 25,000 45,000 Gravel 10,000 15,000 30,000 Soil Contaminated Aggregate Base 3,000 10,000 20,000 Capping Borrow 10,500 10,500 10,500

Table 9.1, continued

Subgrade Soils Typical Silts and Clays (w/ high compressibility) 1,000–2000 Fine Grained Soils with Silts and Clays (w/ low 2,000–3,000 compressibility)

Poorly Graded Sands 3,000–4,500 Gravelly Soils, Well Graded Sands, and Sand/Gravel 4,500–10,000 Mixtures

With an accurate method for measuring in-place moduli with a portable device, a similar table of moduli values based on typical Florida materials could be compiled. Correlations of the actual in-place measurements and future design criteria could be made.

9.3 Proposed Developmental Specifications

Developmental Specifications are specifications developed around a new process, procedure, or material approved for limited use by the State Specifications and Estimates Office. These

specifications are signed and sealed by the professional engineer responsible for authorizing their use and monitoring their performance in the field. A Developmental Specification must be requested from the District Specifications Office on a project-by-project basis.

Developmental Specifications are provided for Section 120 Excavation and Embankment (Soil Compaction Testing with the Dynamic Cone Penetrometer); Section 160 Stabilizing (Stabilized Subgrade Compaction Testing with the Lightweight Deflectometer); and Base Courses Section 200 Rock Base (Base Compaction with the Lightweight Deflectometer).

Equipment and target values vary from section to section.

(Numbering in this section applies only to this section and is based on the Standard Specifications for Road and Bridge Construction.)

EARTHWORK AND RELATED OPERATIONS