for Highway Construction Page 183 of 715 SECTION 301 – GRANULAR SUBBASE
301.01 Description.
Provide, place, and c onstruct 1 or more courses of granular subbase on a prepared subgrade.
301.02 Materials.
Provide materials as specified i n 703. The Engineer will accept granular subbase for quality requirements at the point of delivery. Use the following standard methods for tests: Compaction Standard for Coarse Granular Materials by Use of the Vibratory Spring- load Compactor .............................................................................................. Idaho IT 74 In-Place Density and Moisture Content of Soil and Soil Aggregate by Nuclear Methods (Shallow Depth) ................................................. AASHTO T 310 Method B Prepare and submit an Idah o IT 74 density curve for the subbase material to be incorporated into the work, before placing granular subbase on the roadway. This testing is incidental and a separate payment will not be made. RAP may be used in granular subbase when appr oved. Do not exceed a RAP size of 3 inches. The Engineer will visually verify the RAP daily, in place, to confirm the size requirement has been met.
301.03 Construction Requirements.
A.General. Do not exceed a maximum compacted thickness of 0.8 foot for each layer. Construct the subbase in 2 or more layers of approximate equal thickness if the required compacted thickness of the granular subbase layer exceeds 0.8 foot. The compacted thickness of a single layer of the subbase may be increased to 1 foot when vibrating or other approved types of special compacting equipment are used. The minimum compacted thickness of any course is 1.5 times the maximum particle size. Mix the subbase as specified in 303.03.A. After each layer has been spread, compact the layer for its full width. Continue compaction until at least 95 percent of the maximum dry density is attained as specified in 301.02. Determine the in- place density of granular subbase in accordance with AASHTO T 310 Method B. Maintain the surface of each layer during the compaction operations so a uniform texture is produced and the subbase is firmly keyed. Apply enough water uniformly over the base materials during compaction to ensure proper compaction is achieved.
B.Granular Subbase Material in Stockpile. Provide granular subbase material in stockpiles at designated locations. Stockpile as specified in 303.03.B.
C.Granular Subbase Material, Load, Haul, and Place. Lo ad, haul, and place designated stockpiled granular subbase material on the roadbed. for Highway Construction Page 184 of 71 5 Spread, process, distribute, shape, and compact the granular material as specified in this section . The Department will spe cify location and cost of the stockpiled subbase material.
D.Recycled Asphalt Pavement (RAP). Mix RAP in approximately equal proportions with material meeting the requirements for granular subbase . Ensure the final mix of materials is of uniform consiste ncy. Perform in -place density testing for RAP /subbase mixtures at the frequency specified in this section using the following procedure:
1.Establish the roller pattern by using in- place density from an uncorrected nuclear gauge. The required compaction is achieved and final process rolling is defined as when the final roller pass adds no more than 0.5 pounds per cubic foot to the previous in- place density.
2.Make sufficient additional roller passes to determine that a “false break” or leveling- off point is not used for compaction density.
3.Reestablish the roller pattern when mixture properties in the processed material change and at least every 7,200 square yards of finished surface for each lift.
4.Perform additional tests where soil conditions have changed or as determined by the Engineer to ensure the required compaction is achieved.
301.04 Method of Measurement.
The Engineer will measure acceptably completed work as follows:
1.Granular subbase by the ton or cubic yard. Moisture in the material in excess of 7 percent will not be paid for.
2.Granular subbase in stockpile by the ton or cubic yard.
3.Granular subbase load, haul, and place by the ton or cubic yard. Moisture in the material in excess of 7 percent will not be paid for. RAP, if used in granular subbase, will not reduce the quantity of granular subbase but will be measured as a portion of granular subbase without additional pay.
301.05 Basis of Payment .
The Department will pay for accepted quantities as follows: Pay Item Pay Unit Granular Subbase .................................................................................. Ton or CY Granular Subbase in Stockpile ............................................................... Ton or CY Granular Subbase Load, Haul, and Pl ace .............................................. Ton or CY for Highway Construction Page 185 of 715 SECTION 302 – EMULSION TREATED BASE
302.01 Description.
Construct 1 or more courses of emulsion treated base.
302.02 Materials.
Provide aggregate as specified in 703. The Engineer will accept aggregate for quality requirements at the point of delivery. Provide emulsified asphalt of the type and grade as specified in 702. The Engineer w ill accept the material at the point of delivery. Use the following standard test methods: Compaction Standard for Coarse Granular Materials by Use of the Vibratory Spring- load Compactor ......................................................... Idaho IT 74 In-Place Density and M oisture Content of Soil and Soil Aggregate by Nuclear Methods (Shallow Depth) ................................................. AASHTO T 310 Method B Instead of Idaho IT 74, if approved, the maximum dry density of aggregate base may be tested with: Moisture Density Relations of Soils ..................................................... AASHTO T 180 Method D Prepare an Idaho IT 74 density curve or an AASHTO T 180 Method D moisture- density curve for the aggregate base and submit bef ore placement . This testing is incidental .
302.03 Construction Requirements.
Mix the aggregate , emulsified asphalt , and water in an approved stationary plant. Mix the emulsified asphalt with water at a ratio of 1:1 and uniformly mix with the aggregate base until approximately 4 percent diluted emulsified asphalt, by weight of dry aggregate, has been added. Additional water may be required to complete the mixing of the aggregate base and to facilitate compaction. Place the base material on the roadbed by means of an approved aggregate spreader. Do not exc eed a maximum compacted thickness of 0.5 foot for each layer. Construct the base in 2 or more layers of approximate equal thicknes s if the required compacted depth of the base exceeds 0.5 foot. The compacted depth of a single layer of the base may be increased to 0.8 foot when vibrating or other approved types of special compacting equipment are used. Shaping and spreading may be per formed with motor graders or approved methods in areas where it is not practical to operate the spreader. Compact for its full width after each layer has been spread and continue compaction until 100 percent of the applicable maximum density is attained. Produce a surface for each layer with uniform texture and aggregate that is firmly keyed. Maintain the surface during the compaction operations.
Source: Idaho Standard Specifications for Highway Construction, 2023 Edition. Pages 219–220 of 768.