The following section summarizes the SDDOT’s current compaction practices. This includes materials encountered, methods of base course and subbase compaction quality control, and recycled and salvage material compaction quality control. The current SDDOT Standard Specifications for Roads and Bridges SDDOT (2015a) and interviews with selected members of the SDDOT Technical Panel (SDDOT, 2016) were utilized as the basis for this section.
2.8.1 Materials Encountered and Gradation Requirements
The requirements for acceptance of Aggregates for granular bases are defined in Sections 882.1 to 882.3 of the South Dakota Department of Transportation Standard Specifications (SDDOT, 2015a).
Specific requirements for grain size distribution are provided in Table 4. The SDDOT use SD 103 to classify materials according to the AASHTO M 145 classification system.
Table 4: SDDOT Specific Requirements for Aggregate Acceptance (SDDOT, 2015a).
Requirements Subbase Gravel Cushion
Specific requirements for various milled, reclaimed and salvaged material are found in Section 884.2 of the South Dakota Department of Transportation Standard Specifications (SDDOT, 2015a).
Reclaimed Asphalt Pavement (RAP) along with Salvaged materials such as subbase, base course, and gravel surfacing all have the same required specific grain size distribution requirements of 100 percent must pass the 1.5 inch sieve and 95-100 percent must pass the 1 inch sieve.
According to the SDDOT Minimum Sample and Test Requirements (MSTR), when quality tests are required by specification, one sample per 50,000 tons shall be submitted to the SDDOT’s Laboratory for testing. Aggregate production from the same source used by one or more projects at the same time only require a single minimum test frequency for quality assurance. The sample size is specified as 120 pounds in 4 bags. Tests are not required for quantities less than 100 ton per day or 500 ton per project (SDDOT, 2015a).
2.8.2 Methods of Base Course and Subbase Compaction Quality Control SDDOT’s current methods for compaction control of various granular material is defined in Section 260.3 of the South Dakota Department of Transportation Standard Specifications (SDDOT, 2015a). Base Course material is to be compacted to 97 percent of maximum dry density. The maximum dry density is determined by the SD 104 Method 4 (SDDOT, 2015b) which has close relation to the
AASHTO T 272-15 (AASHTO, 2015c). This method is known as a one-point determination used for more rapid determination of target density when compared to the AASHTO T 180 (AASHTO, 2015c), which is the four-point equivalent. The method requires compacting a single point at approximately optimum moisture in a standard 6-in mold in similar manner to the AASHTO T 99 (AASHTO, 2015b).
A wet density and moisture is determined for the single point and is entered into the family of
compaction curves. The curve that is closest to the wet density and optimum moisture is then adopted as the family curve for that material. The corresponding dry density is then adopted as the target density for the material tested. The SDDOT currently requires a one-point determination for every in-place density tests conducted to establish an individual target density for each test. The one-point
determination uses material from or adjacent to the hole for each in-place test. If the one-point moisture content deviates from optimum (for the curve selected) by more than 2 percentage points below or 1 percentage point above, a second one-point is required at or nearer to optimum and within the stated tolerance stated by the SD 104 (SDDOT, 2015b).
Prior to the first in-place density test, a single four-point determination of maximum dry density and optimum moisture is determined for the base course materials to be tested. The four-point determination is conducted in accordance with the SD 104 Method 3 (SDDOT, 2015b). A four-point determination is required to verify if the family of compaction curves is suitable for the material. Once a four-point determination of dry density and optimum moisture is determined, it is compared to the one-point determinations required for each in-place density. When the one-point determination deviates more than 3 pounds from the four-point results, another one-point determination is conducted.
Similarly, if moisture in the one-point determination deviates more than 2 percentage points below or 1 percentage point above optimum moisture, another one-point (nearer to optimum moisture) or a new four-point determination should be conducted.
In-situ field density of base course and subbase is determined by one of the following methods:
1.) SD 105: Density of soils / Granular Material In-place by Sand-Cone Method (SDDOT, 2015c)
2.) SD 110: Density of Granular Material by Modified Sand-Cone Method for Thin Layers (SDDOT, 2015d)
3.) SD 114: Determination of In-place Density of Soils and Aggregates by Nuclear Method (SDDOT, 2015e)
The most common test method for base course materials in South Dakota is SD 105 (SDDOT, 2015c).
Each of SDDOT’s four regions contains six NDG totaling 24 gauges in all (SDDOT, 2016). In-place density tests are conducted every mile, per lift, per roadbed surface just prior to application of prime or subsequent course according to the SDDOT MSTR (SDDOT, 2015a).
2.8.3 Methods of Recycled and Salvaged Compaction Quality Control
A growing practice of the SDDOT is recycling or reclamation of pavement surfaces, bases courses and subbases. Materials classified as recycled materials can be placed into a stockpile while materials classified as reclaim remain in place and are used to form the new road bed. FDR is defined by the processing and blending the asphalt mix and granular base material and placing, watering, shaping, and compacting the material to the typical section (SDDOT, 2015a). The materials are to meet the standard specifications of asphalt mix and granular base materials outlined in Section 884.3 of the South Dakota Department of Transportation Standard Specifications (SDDOT, 2015a). The FDR process is outlined in Section 280 of the SDDOT Standard Specifications, Section 280.B, and states that material is to be placed in a minimum of two lifts and lift thickness shall not exceed 4-in in depth (SDDOT, 2015a).
“Section 280.3.C. Compaction and Density Requirements” states that each compacted layer shall meet a minimum of 95 percent of the target dry density established by Method SD 219 (SDDOT, 2015f) and material shall have a minimum moisture content of 4 percent uniformly blended throughout the depth of the lift of material (SDDOT, 2015a).
Method SD 219 requires use of a test strip with a minimum length of 500 feet. Four tests sites are selected throughout the test strip (typically in the middle 300 feet). A NDG calibrated and
standardized in accordance with SD 114 (2015e) is used to determine the wet density at each test location within the test trip. The test rod of the NDG is inserted into the material so that it is as close to the bottom of the lift as possible but not within 1 inch of the bottom of the layer. Once density is measured, a roller makes four passes over the test strip “one series”. After completion of four passes or
one series, the NDG is again used to measure wet density at each test location. The average wet density of each series is recorded on the DOT-28 test form. This process is repeated for each series until the increase in average wet density is less than 1.0-pcf. At this time, samples of the material directly below the four NDG test locations are immediately placed in an airtight container for moisture testing. SD 108, is an oven drying method used to determine the moisture content of the material (SDDOT, 2015g).
The target dry density is then determined by averaging the four dry density measurements. A minimum of one test strip is performed for each lift. However, the field technician can require additional test strips when there is a significate change in aggregate type, weather conditions, or other controlling factors to check target density. The test strip becomes part of the constructed roadway upon completion of the work (SDDOT, 2015a).
In-place density determinations using Method SD 219 is performed using the NDG. These tests are conducted in the same manner as those previously discussed to determine dry density of the test strip. Moisture determination is conducted for each in-place density test using Method SD 108:
Oven Drying Method and the dry density and percent compaction is subsequently calculated (SDDOT, 2015a).