312CRUSHED AGGREGATE BASE COURSE, TYPE DG

312.1DESCRIPTION—This work is construction of a dense graded stone, gravel, or slag base course,

uniformly premixed with a predetermined quantity of water. When placed on subgrade, it includes the preparation of subgrade, as specified in Section 210.

312.2MATERIAL—

courses. Acceptable granulated blast-furnace slag, as specified in Section 350.2, meeting the gradation requirements specified in Table A, may be used.

the final compacted mixture meets the specified gradation within limits of the reviewed job-mix formula.

Add sufficient water to the mixture to provide optimum moisture content at the time of compaction. Do not vary this quantity by more than 2 percentage points from the optimum moisture, as determined according to PTM No. 106, Method B.

To maintain specified criteria throughout the progress of work, at least twice daily analyze samples of the completed mixture taken at the plant or after spreading. Unsatisfactory results or changes in the supply source may require a change in the JMF. The supply source may be changed, if allowed. Maintain accuracy of control so at least 90% of test samples fall within the tolerance limits of Table A. Remove and replace material failing to meet this requirement.

TABLE A COMPOSITION OF MIXTURE (Weight Percent Passing Square Openings Based on Laboratory Sieve Tests)

SIEVE SIZE PERCENT PASSING TOLERANCE LIMITS OF THE APPROVED JMF 2 inches 100 3/4-inch 52-100 ± 8% 3/8-inch 36-70 ± 8% No. 4 24-50 ± 6% No. 16 10-30 ± 6% No. 200 0-10 ± 3%

312.3CONSTRUCTION—

Measure the coarse and fine material separately, by either volume or weight, and feed into the mixer

in proper proportions and at a rate to ensure correct blending. Measure added water by weight, volume, or a metering device, and uniformly distribute in the mix. Use mixing plants equipped with automatic cutoff devices, which stop the feed to the mixer if delivery of any component of the mix stops. Provide means to check and verify the accuracy of the proportioning and measuring devices. Stockpile aggregates for proportioning, by any acceptable method, in a manner that will prevent segregation and degradation of aggregates. Use mass-proportioning plants, equipped with separate bins for each size aggregate.

base material without segregation.

materials. Distribute measured water uniformly by means of a spray system and continue mixing until materials have been combined into a homogeneous mixture. Do not place materials containing either frost or frozen pieces into the mixture. When directed, add calcium chloride to the mixture, before adding water, to maintain required moisture. Proportion and uniformly blend calcium chloride, at the rate of 7 pounds per ton of mixture for Type 1 and 5.7 pounds per ton of mixture for Type 2.

vehicles, free of harmful material. To prevent loss of moisture during transportation, cover mixture with suitable covers, if necessary, until deposited in the spreader. Frequent moisture control tests will be made at the point of delivery on the project, as directed.

replacement. Remove pavement in these areas to neat lines, as specified in Section 203.

at least 1,500 feet in advance of the leading spreader; keep free of ruts, irregularities, and loose materials.

of base course, before placing base course or build up and roll shoulders simultaneously with compaction of each layer.

more layers of approximately equal depth, with no layer less than 3 inches nor more than 6 inches in depth. Place mixture to provide positive bond and uniform compaction between abutting lanes. Accomplish this by working spreaders in echelon or by alternating spreaders frequently between lanes, to minimize moisture loss. In locations where machine spreading is impractical, spread manually or by other acceptable methods. Supply sufficient equipment to spread, shape, and compact mixture at the rate produced by the mixing plant. Complete all operations relating to construction of base course during daylight hours. Do not place mixture on a frozen surface, when air temperature is below 40 F, or when freezing temperatures are forecast to occur within the next 24 hours. To ensure proper bonding between layers of base course, place succeeding layers as soon as practical. Keep base layers moist until covered by the next layer. Do not cut into an underlying completed layer, except as directed for repairs or corrections. Maintain the proper moisture content in the mixture at all stages of construction, including vertical faces of part -width spread material, to assure positive bonding of abutting lanes.

specified in Section 312.3(f), unless otherwise directed.

density, determined according to PTM No. 106, Method B. Determine field density, according to AASHTO T 191. When material is too coarse to use these methods, compaction will be determined, based on nonmovement of material under specified compaction equipment. Where density in any layer fails to meet specified requirements, additional compaction will be required. If the density cannot be obtained by additional compaction, thoroughly loosen, remoisten, reshape, and recompact the entire area of the layer with low density. If required density cannot be obtained, remove and replace the affected area with a new mixture that can be compacted as required.

Equip the template with metal or other vertical extensions attached to each end, so the bottom of the template will be at the elevation of the top of the base course. Furnish at least three templates. Test the cross section for surface irregularities at intervals of not more than 25 feet. Install string lines with ample supports, offset along each side to control the elevation and depth of the base course. Maintain string lines until the base course is completed and the deficiencies have been corrected. Use a 10 -foot straightedge to test for longitudinal irregularities in the surface of the base course. Hold the straightedge parallel to the road centerline in contact with the surface. Move the straightedge from one side of the base course to the other. Advance along the base course in 5-foot increments. For surface irregularities exceeding 1/2-inch, immediately correct as follows: Blade off high spots, as directed, provided the surface is left in a uniformly smooth and dense condition. If high spots cannot be removed by blading, loosen the top layer through its full depth over the affected area, remove excess material, and provide m oisture in proper quantity to reshape and recompact to the specified density. If high spots cannot be satisfactorily corrected by either of these methods, remove the top layer over the affected area and reconstruct with a new mixture. Where it is necessary to add material to low spots, loosen the top layer over the affected area. Incorporate additional material, correctly graded, into the loosened material. Reshape and recompact the entire area at the proper moisture content. If the resulting surface is still unsatisfactory, remove the top layer over the affected area and reconstruct with a new mixture. Do not skin patch or fill low spots with small amounts of material. Refer to Section 210.3(d) for GPS or Laser Controlled Equipment.

for each 3,000 square yards or less. The Representative will measure the depth of the base course. The initial bed and filler layer of fine material is considered part of the base course for determining the final compacted depth. Remove and replace any area in which the depth is 1/2-inch or more deficient. Additional test holes may be required, if directed, to determine the limits of replacement areas. After the depth has been measured, backfill test holes with acceptable material and compact.

moisten the end of existing base course, blend with new mixture, and compact to form a continuous section, without a joint.

a granular texture free of loose material and treat the surface with a single application of asphalt material, at a rate not to exceed 0.15 gallon per square yard of base course.

course, as specified in Section 901.3(b). Maintain and protect base course opened to traffic by authority of the Representative, as specified in Sections 107.15 and 901. Allow only necessary local traffic and essential construction equipment on the base course, unless otherwise directed. Repair or replace marred, distorted, or otherwise damaged pavement.

312.4MEASUREMENT AND PAYMENT—