3-1 Chapter 3 DIVISION 300 - BASES SECTION 301 Through 303 - VACANT SECTION 304 - AGGREGATE BASE AND SUBBASE COURSE
304.01 Description This work shall consist of furnishing and p lacing one or more
courses of aggregates on a prepared surface in accordance with the specifications in reasonably close conformity with the lines, grades, thickness a nd typical cross sections, as shown on the plans or established.
304.02 Aggregate Aggregates shall conform to the requirements specified in the
following subsections of Division 700 - Materials: Aggregate Base Type A & B 703.06 a Aggregate Base Type C 703.06 b Aggregate Subbase Type D & E 703.06 c Aggregate for base or subbase courses shall be material meeting the aggregate type requirements specified in the following table: Material Aggregate Type (Subsection 703.06) Base Course, Crushed 1A, B or C Subbase Course, Gravel 2D 1Will be designate d on the plans 2Subbase Course, Gravel-Type E may be used below the top 9 ” of the subbase layer at the Contractor ’s option For the various types of base and subbase, all shall conform to the gradation requirements of the contract at the time it is deposited on the roadbed. The Depart ment will obtain samples from the roadbed for Acceptance prior to compaction. Oversized stones sh all be removed from the aggregate before depositing on the r oadway. Oversized stones fo r the various types are as follows: Type A will not pass a 2 inch square mesh sieve Type B and Type C will not pass a 4 inch square mesh sieve Type D and E will not pass a 6 inch square mesh sieve.” The top 3” of Aggregate Base Course-Type C shall consist of Rec ycled Asphalt Pavement (RAP) or Untreated Aggregate Surface Course-Type B. 3-2
304.03 Placing The maximum compacted thickness of any base or subbase course layer
shall not exceed 12 inches unless the Contractor demonstrates b y a test section that the required compaction can be obtained. If compacted layers more than 12 inches are allowed, the Contractor shall agree to make the necessary excavations an d backfilling in the course for the Resident to determine the density. When layers are constructed of differently graded aggregate, f ine grading of the lower layer will not be required except when millings are place d as the upper most layer. In this case the coarse graded base layer shall be fine graded to +/- ¾ inch and compacted to the required specification prior to placing the layer of millin gs. The layer of millings shall then be placed, shaped, and compacted within the tolerances spe cified below. Each layer of aggregate shall be placed over the full width of the section except, the Resident may authorize the Contractor to place less than full w idth layers, when existing traffic or other conditions restrict operations over the full w idth of the section. When the Contractor places material to complete the full width, the expo sed edge of the previously placed aggregate shall be cleaned of all contamination before a dditional base or subbase aggregate is placed adjacent to it. Aggregate base and subbase courses may be placed upon frozen s urfaces when such surfaces have been properly constructed. The material as spread shall be well mixed with no pockets of either fine or coarse material. Segregation of large or fine particles will not be a llowed.
304.04 Shaping, Compacting and Stabilizing Compaction of each layer of base and
subbase shall continue until a density of not less than 95% of the maximum density has been achieved for the full width and depth of the layer. The maximu m density shall be determined in accordance with AASHTO T180, Method C or D, corre cting for oversize particles except mixtures may have 40 percent or less retained on the ¾ inch sieve. Field density tests will be performed by the Department in accordance with AASHTO T 310. Compaction of each layer of base or subbase material that excee ds 40 percent retained on the ¾ inch sieve shall continue until a density of not less than 98% of the maximum density has been achieved for the full width and depth of the l ayer. Density tests and the maximum density determined by a field proctor shall be performe d by the Department. The surface, compaction and stability, shall be satisfacto rily maintained until the pavement course has been placed. If required, additional water and fine material shall be applied to prevent checking, raveling or rutting. If the top of any layer becomes contaminated by degradation of the aggregate or addition of foreign material, the contaminated material shall b e removed and replaced with the specified material.