3-1 DIVISION 300 SUBBASE AND BASE COURSES SECTIO N 301 – SUBBASE 301.0 1 DESCRIPTION . This work shall consist of furnishing and placing one or more courses of approved gravel, crushed gravel, dense graded crushed stone, or other proportioned material on a prepared surface or at other locations. 301.0 2 MATERIALS . Materials shall meet the requirements of the following subsections: Coarse Aggregate for Concrete ................................ ................................ .................. 704.02 Gravel for Subbase ................................ ................................ ................................ .....704.04 Crushed Gravel for Subbase ................................ ................................ ...................... 704.05 Dense Graded Crushed Stone for Subbase ................................ ................................ 704.06 Processed Glass Aggregate ................................ ................................ ........................ 704.20 Recycled Concrete Aggregate ................................ ................................ .................... 704.21 At the option of the Contractor, unless otherwise specified in the Contract, processed glass aggregate (PGA) meeting the requirements of Subsection 704.20 or recycled concrete aggregate (RCA) meeting the requirements of Subsection 704.21 may be used to partially replace natural aggregate in materials specified to meet the requirements of Subsection 704.04 , Subsection 704.05 , or Subsection 704.06 . PGA subbase blends shall not contain more than 20% PGA by weight. RCA subbase blends shall not contain m ore than 25% RCA by weight. In no case shall PGA and RCA be combined in subbase. The final blend shall conform to the specified gradation for the subbase material. The blending process shall be complete to ensure that as thorough a distribution and as unif orm a mixture as practicable has been obtained. In -place blending of PGA with other materials will not be permitted. When specified for use on the project or as directed by the Engineer, RAP subbase shall include milled grindings which have been screened or crushed by the Contractor such that 100% pass the 1 -1/2 inch (37.5 mm) sieve prior to blending. The grindings shall be blended in equal proportions (50% by weight) with material meeting the requirements of fine graded crushed gravel for subbase as specified in Table
704.05 A.
3-2 301.0 3 GENERA L CONSTRUCTIO N REQUIREMENTS . The subbase material shall be placed on a prepared surface with an approved spreader box or by use of other approved mechanical spreading equipment . Dumping directly on the subgr ade will not be permitted. A bulldozer may be used instead of a spreader box, provided that the subbase material is first placed on the previously laid subbase and then completely removed from the area where it was first deposited. Should segregation of th e subbase occur, the Contractor shall remove and replace the material or rework it until uniform grading is obtained. If material below subgrade becomes intermixed with the subbase , resulting in an unacceptable product, the mixture shall be removed and replaced with new subbase material . Frozen material shall not be used in the construction of subbase. Subbase material shall not be deposited on frozen subgrade, and successive layers shall not be placed on material that has frozen. The maximum compacted layer thickness for all subbase material s is 12 inches. Where the finished depth of the subbase is to be greater than 12 inches, it shall be placed and compacted in two or more layers of approximately equal thickness. In the placement of layers, all joints shall be staggered at least 12 inches. After each layer of subbase material is placed, it shall be graded to obtain a smooth, even surface as specified in Subsection 301.05 . Following grading operations, the subbase shall be thoroughly compacted as specified in Subsection 301.06 . If required, water shall be uniformly applied over the subbase material s during compaction in the amount necessary for proper consolidation. Care shall be tak en to prevent excessive moisture contents in subbase materials prior to compaction. Materials containing PGA or RCA shall be compacted in the same manner as material s that do not contain recycled material s. If needed, the Contractor may use material meetin g the requirements of Table 704.02 C as filler to achieve the design grade when the variation of the surface is less than 1 inch. When it is necessary to maintain traffic over the subbase , half of the width of the roadway shall be constructed at a time. The portion under construction shall have the subbase material placed, graded, and compacted before opening to traffic. Subsequent traffic damage to the material shall be entirely the Contractor’s responsibility. If the subbase loses its shape, the Contractor shall loosen, regrade, and compact as necessary. When it is necessary to maintain traffic over the subbase , or where construction hauling occurs over the subbase , the upper 2 inches of subbase shall be scarified (to res tore permeability in the subbase surface), compacted, and regraded as required, or replaced just prior to the placement of any pavement. 3-3 301.0 4 SPECIFI C CONSTRUCTIO N REQUIREMENTS .
a.Subbase of Gravel . Only uniformly graded gravel from the pit shall be used. The Contractor shall manipulate the material in the pit to eliminate non -uniformly graded pockets of material .
b.Subbase of Crushed G ravel . When stockpiling, care shall be taken to prevent segregation in the pile.
c.Subbase of Dense Grade d Crushed Stone . When stockpiling, care shall be taken to prevent segregation in the pile. 301.0 5 SURFAC E TOLERANCE . The surface of the compacted subbase will be tested by the Engineer at selected locations. The variation of the surface shall at no point exceed 1 inch. This variation shall not be maintained for a distance longer than 50 feet. The required cr own and superelevation shall be maintained. All humps or depressions exceeding the specified tolerances shall be corrected by reshaping or removing defective work and replacing it with new material as directed by the Engineer. Any new material used to replace removed material shall meet the applicable gradation in Subsection 301.02 . 301.0 6 COMPACTION . Compaction of each layer shall continue until a density of not less than 95% of the maximum dry density has been achieved. When 1,000 cubic yard s or more of subbase material is to be placed as part of the Contract, the maximum dry density shall be determined by the Contractor in accordance with AASHTO T 180 , Method D , as modified by the Agency’s Materials Testing and Certification Section. Laborat ory moisture -density tests shall be performed to ensure a standard error of the mean maximum dry density of less than 1 pcf . This will necessitate at least five, but no more than ten, replications of the test. The Contractor shall provide the Engineer with all test results and calculations for determining the maximum dry density, at least 10 calendar days prior to subbase placement . The maximum dry density shall be determined after any change in source, regardless of quantity, and confirmed by repetition of the selected test method at a frequency of 1,000 cubic yards when the prescribed standard error can be attained by five or less replicate tests. If more than five replicate tests are required to meet the prescribed standard error, the maximum dry density shall be confirmed at a frequency of every 5,000 cubic yards. The Engineer may reduce this frequency with the approval of the Geotechnical Engineering Manager after the initial two maximum dry density determinations. 3-4 When fewer than 1,000 cubic yards of subbase material are to be placed as part of the Contract, the maximum dry density will be determined by the Agency in accordance with AASHTO T 180 , Method D , as modified by the Agency’s Materials Testing and Certification Sectio n. Field density testing will be performed by the Agency in accordance with AASHTO T 310 at locations determined by the Engineer. Compaction operations shall proceed such that the target field density as determined in accordance with this subsection is ach ieved. 301.0 7 METHO D OF MEASUREMENT . The quantity of Subbase of Gravel; Subbase of Crushed Gravel, Coarse Graded; and Subbase of Crushed Gravel, Fine Graded to be measured for payment will be the number of cubic yards of the type specified for use in the complete and accepted work , as determined by the plan dimensions of the compacted material , including any filler material used to achieve the design grade. When specified to be paid by weigh t, the quantity of Subbase of Crushed Gravel, Fine Graded to be measured for payment will be the number of tons of material in place in the complete and accepted work , as determined from the load ticket s. The quantity of Subbase, RAP to be measured for payment will be the number of tons of material in place in the complete and accepted work , as determined from the load ticket s. When subbase material is required for extra depth at bridge approaches, the quantity to be measured for payment will be the number of cubic yards measured in place for this p urpose between the lines shown on the Plans. Materials containing PGA or RCA will be measured in the same manner as subbase material s that do not contain PGA or RCA. 301.0 8 BASIS OF PAYMENT . The accepted quantity of Subbase of Gravel; Subbase of Crushed Gravel, Coarse Graded; Subbase of Crushed Gravel, Fine Graded; and Subbase, RAP will be paid for at the Contract unit price per cubic yard or ton for the type specified. Payment will be full compensation for furnishing, blending, transporting, testing, placing, grading, and compacting the material specified and for furnishing all labor, tools, equipment , and incidentals necessary to complete the work . No additional payment will be made for filler material used as a replacement for the specified subbase material . 3-5 No payment will be made for the following:
a.Material forced into or mixed with the subgrade material .
b.Material placed to a depth greater than shown on the Plans.
c.Water used to obtain required compaction.
d.Removal and replacement of subbase material .
e.Scarifying, recompacting, or regrading of subgrade or subbase layers, when required. Payment will be made under: Pay Item Pay Unit
301.15 00 Subbase of Gravel ................................ ................................ ..................... Cubic Yard
301.25 00 Subbase of Crushed Gravel, Coarse Graded ................................ ............. Cubic Yard
301.26 00 Subba se of Crushed Gravel, Fine Graded ................................ ................. Cubic Yard
301.28 00 Subbase of Crushed Gravel, Fine Graded ................................ ................. Ton
301.35 00 Subbase of Dense Graded Crushed Stone ................................ ................. Cubic Yard
301.40 00 Subbase , RAP ................................ ................................ ........................... Ton
3-6 SECTION 310 – FULL DEPTH RECLAMATION
310.01 DESCRIPTION . This work shall consist of performing full depth reclamation (FDR) by
pulverizing the existing pavement together with underlying base course material, mixing with water, fine grading, and compacting the homogenous base mate rials to the depth, width, and desired density specified in the Contract.
310.02 MATERIALS . Materials shall meet the requirements of the following subsections:
Water ................................ ................................ ................................ .......................... 745.01 The pulverized material shall consist of the existing pavement blended with underlying subbase material and additional aggregate material and shall conform to the gradation requirements of Table 310.02A . TABLE 310.02A – FDR GRADATION REQUIREMENTS Sieve De signation Percentage by Mass (Weight) Passing Square Mesh Sieves 3 inch (75.0 mm) 100 1-1/2 inch (37.5 mm) 80 – 100 No. 4 (4.75 mm) 30 – 60
310.03 Equipment .
a.General Requirements . Any additional equipment used by the Contractor beyond th at specified below shall be approved by the Engineer based on its suitability to produce results meeting the specification requirements.
b.Reclamation . The Contractor shall use a self -propelled, traveling rotary reclaimer or equivalent machine capable of cutting through existing roadway material to depths of up to 16 inches with one pass. The equipment shall be capable of pulverizing the existing paveme nt, base, and subgrade in-place, and mixing any added materials to the specified depth. The cutting drum shall have the ability to operate at various speeds (rpm), independent of the machine’s forward speed, to control oversized material and gradation. The Contractor shall provide and use equipment that will produce the completed FDR base as specified herein. The Contractor shall maintain all equipment in a satisfactory operating condition. Equipment such as road planers or milling machines designed to mi ll or shred the existing roadway materials rather than crush or fracture the materials are not allowed as an alternative to the reclaimer.
Source: Vermont Standard Specifications for Construction, 2024 Edition. Pages 289–293 of 1,380.