for Highway Construction Page 191 of 71 5 SECTION 307 – OPEN- GRADED BASE
307.01 Description.
Construct 1 or more courses of open- graded base on a prepared surface.
307.02 Materials.
Provide material for open- graded base as specified in 703.
307.03 Construction Requirements.
Place the first layer of open- graded base directly over Type II subgrade separation geotextile in a lift of at least 12 inches thick but less than 18 inches thick. The minimum lift thickness is 6 inches and the maximum lift thickness is 12 inches above the initial lift. Compact the first layer with at least 6 full coverages and compact subsequent layers with at least 2 full coverages for each 6- inch lift thickness with a vibratory roller meeting the following requirements:
1.A rated minimum centrifugal force of 30,000 pounds per impact.
2.At least 1,000 vibrations per minute.
3.Operate at a speed less than 130 feet per minute. Do not allow equipment on the geotextile before placing the firs t lift of open -graded base. Do not dump the open- graded base directly on the geotextile. Dump the material on the previously placed lift and push ahead. Switch off the vibrators if there is evidenc e of the vibrating rollers causing excess movement, depressions, or voids other than what is considered normal compaction displacement until otherwise directed. During the compaction process, keep the open- graded base visibly moist. Keep soil, mud, or other undesirable fine material from accumulating on its surface once t he open- graded base is in place. If contamination does occur during the construction operation, replace material as directed at no cost to the Department. Place open- graded base Class III as specified in 303.
307.04 Method of Measurement.
The Engineer will measure acceptably completed work by the cubic yard, neat line measurement of the roadway section, or the ton.
307.05 Basis of Payment .
The Department will pay for acceptable quantities at the contract unit prices as follows: Pay Item Pay Unit Open- graded base Class ...................................................................... CY or Ton The Department will pay for geotextile under 640. for Highway Construction Page 192 of 715 SECTION 308 – CEMENT RECYCLED ASPHALT BASE STABILIZATION (CRABS)
308.01 Description.
Recycle the existing roadway pavement and a portion of the base layer to the lines , grades , and thicknesses of the typical sections. Accomplish the CRABS work in 4 steps:
1.Prepare roadbed.
2.Pulverizing the existing pavement .
3.CRABS (adding cement and mixing).
4.Shaping and compacting. Follow the specified grade control class.
1.Class I CRABS: use field -established elevations.
2.Class II CRABS: use prescribed elevations.
308.02 Materials.
Use materials conforming to the following requirements:
1.Portland Cement . Use cement as spec ified in 701.
2.Water. Use water that is reasonably clear and without oil and other contaminates.
3.Testing. Perform quality control density testing using an uncorrected nuclear gauge in accordance with FOP for AASHTO T 310 Method A. Conduct at least 1 compaction test for every 7,200 square yards of CRABS work.
308.03 Construction Requirements.
Before mobilization, submit a plan of operations for CRABS processing, including traffic control.
A.General.
1.Weather Limitations . Construct the CRABS while the existing pavement temperature is above and is exp ected to remain above 40°F for 24 hours after final completion. Do not spread portland cement over puddled water, during rain, w hen rain is imminent, or when wind will not allow uniform spread on the roadway.
2.Operational Restriction. Add cement and process no more of the roadway than can be repaved in 2 days of paving production.
3.Traffic Control. Unless the approved traffic control plan requires traffic to be detoured to an alternate roadway, open the roadway to traffic at the end of each working day by either re- laying the unprocessed pulverized material and compacting firmly or adding cement and processing for a finished product.
4.Grade Control Requirements.
a.On Class I work, establish the final CRABS surface elevation in the field. Finish the CRABS surface to within 0.03 foot of the field -established elevation and provide the field- established or specified cross slope at 12 feet from centerline and at the edge of the CRABS surface.
Source: Idaho Standard Specifications for Highway Construction, 2023 Edition. Pages 227–227 of 768.