Georgia Micro Mill Spec

Date:      May 24, 2006
Section 432—Mill Asphaltic Concrete Pavement
Retain Section 432 and add the following:
Section 432—Mill Asphaltic Concrete Pavement (Micro-Mill)
432.1 General Description
This work includes micro-milling of existing asphaltic concrete pavement to remove wheel ruts and other surface irregularities, restore proper grade and/or transverse slope of pavement as indicated in the Plans or as instructed by the Engineer. The planed surface shall provide a texture suitable for use as a temporary riding surface or an immediate overlay with OGFC or PEM with no further treatment or overlays. The use of the micro-milled pavement as a temporary riding surface shall be for a maximum of seven days. Perform the work according to these Specifications and Plan details.
432.1.02 Related References
B.    Referenced Documents
GDT 126
432.3 Construction Requirements
432.3.02 Equipment
C.    Micro-milling Equipment
Use power-driven, self-propelled micro-milling equipment that is the size and shape that allows traffic to pass safely through areas adjacent to the work. Also, use equipment that is:
·      Equipped with a cutting mandrel with carbide tipped cutting teeth designed for micro-milling bituminous pavement to close tolerances.
·      Equipped with grade and slope controls operating from a stringline or ski and based on mechanical or sonic operation
·      Capable of removing pavement to an accuracy of 1/16 in (1.6 mm)
·      Furnished with a lighting system for night work, as necessary
·      Provided with conveyors capable of side, rear, or front loading to transfer the milled material from the roadway to a truck
432.3.05 Construction
B.    Micro-milling Operation
Follow the Plans to micro-mill the designated areas and depths including bridge decks, shoulders, and ramps, as required. Ensure the following requirements are met:
1.       Prior to commencement of the work, construct a test section that is 1000 feet in length with a uniformly textured surface and cross section as approved by the Engineer.
·         The final pavement surface shall have a transverse pattern of 0.2 in. (5 mm) center to center of each strike area. The difference between the ridge and valley of the mat surface shall not exceed 1/16 in. (1.6 mm).
·         Surface acceptance testing will be performed using the Laser Road Profiler in accordance with GDT-126. The measured indices must meet a target of 825 mm/km in the test section. 
·         If any of these requirements are exceeded in the test section, work shall be halted and the contractor shall submit a written plan of action detailing what steps will be taken to improve operations. If approved by the Engineer, the contractor will construct another 1000 ft test section. This test section shall be located in a different area than the initial section using the approved corrective action. This designated section shall be micro-milled to conform to the same requirements as those required in the initial test section. The contractor shall not be allowed to start continual micro-milling until an acceptable test section is obtained. 
2.       Micro-milling methods that will produce a uniform finished surface and maintain a constant cross slope between extremities in each lane.
3.       Provide positive drainage to prevent water accumulation on the micro-milled pavement, as shown on the Plans or directed by the Engineer.
4.       Bevel back the longitudinal vertical edges greater than 2 in (50 mm) that are produced by the removal process and left exposed to traffic. Bevel them back at least 3 in for each 2 in (75 mm for each 50 mm) of material removed. Use an attached mold board or other approved method.
5.       When removing material at ramp areas and ends of milled sections, taper the transverse edges 10 ft (3 m) to avoid creating a traffic hazard and to produce a smooth surface.
6      Protect with a temporary asphaltic concrete tie-in (paper joint) vertical edges at other areas such as bridge approach         slabs, drainage structures, and utility apputenance greater than 1/2 in that are left open to transversing vehicles. Place              the temporary tie-in at taper rate of at least 6 to 1 horizontal to vertical distance.
7      Remove dust, residue, and loose milled material from the micro-milled surface. Do not allow traffic on the milled      surface and do not place asphaltic concrete on the milled surface until removal is complete.
432.3.06 Quality Acceptance
Ensure that the micro-milling operation produces a uniform pavement texture that is true to line, grade, and cross section.
Micro-milled pavement surface acceptance testing will be performed using the Laser Road Profiler method in GDT 126. Micro-milled pavement will be evaluated on individual test sections, normally 0.50 mile (0.50km) long. Indices must target 825 mm/km and not exceed the correction index of 900 mm/km.
Micro-milled pavement surfaces are subject to visual and straightedge inspections. Keep a 10 ft. straightedge near the micro-milling operation to measure surface irregularities of the milled pavement surface. Any areas exceeding 1/8 in (3.2 mm) between the ridge and valley of the mat surface or fail to meet pavement surface acceptance testing using The Laser road Profiler shall require that the underlying layer be removed and replace with material as directed by the Engineer at no additional cost to the Department. All corrective work shall be preformed in a minimum 1000 ft section.
Ensure that the cross slope is uniform and that no depressions or slope misalignments greater than 1/4 in per 12 ft (6 mm in 3.6 m) exist when the slope is tested with a straightedge placed perpendicular to the center line.
432.4 Measurement
Micro-milling existing asphaltic concrete pavement is measured by the square yard (meter) as described in Subsection 109.01, “Measurement and Quantities.”
432.5 Payment
Micro-milling asphaltic concrete pavement, measured as specified, will be paid for at the Contract Unit Price bid per square yard (meter). No adjustment in the unit price for this item or other items will be considered for variations in the amount of RAP actually recovered.
Payment is full compensation for furnishing equipment, micro-milling, hauling, stockpiling milled material, and satisfactorily performing the work.
The reclaimed asphaltic pavement becomes the Contractor’s property unless otherwise specified.
Payment will be made under:
Item No. 432
Micro-mill asphaltic concrete pavement, ___ in (mm) depth
Per square yard (meter)