The cement treated free draining base (CTFDB) is to be a mixture of coarse aggregate, Portland cement and water.
The coarse aggregate used can be either No. 57 or No. 67 size per Table 703.01-1.
The Contractor must proportion, mix and transport the CTFDB according to Item 499.
The mix is to be prepared as follows:
Use a minimum cement content of 250 pounds per cubic yard (148 kg/m³) when using No. 57 size coarse aggregate and it must be 220 pounds per cubic yard (130 kg/m³) when using No. 67 size.
The water-cement ratio is to be 0.36.
A water- reducing admixture meeting 705.12 can be used.
The Contractor must submit a mix design for the proposed CTFDB 30 days prior to the start of production. This mix design must describe the proposed aggregate size, the cement content and the water content by weight. A private laboratory must perform tests on the proposed mix to verify the yield of the mix design.
Inspection should include random sampling of the CTFDB material delivered to the project to ensure conformance to the mix design. The unit weight of the mix must be determined and the yield checked.
The Contractor must provide all equipment necessary to mix, transport, place, compact and finish the CTFDB. Equipment must be approved before the work begins.
A spreader must be used if the width being placed is more than 12 feet (3.6 m) or the total area of any given width exceeds 5000 square yards (4000 m²) of area. The spreader could be a concrete spreader or an asphalt paving machine.
Initial compaction may be done by using a steel wheel roller, a modified slip-form paving machine with vibratory plates or high-density screed pavers. Compaction must not crush aggregate particles or cause segregation. Final compaction must be done with steel wheel rollers weighing 6 to 10 tons (5 to 9 metric tons). If vibratory rollers are used, do not use them in vibratory mode.
Spreading with an Asphalt Paving Machine
Spreading CTFDB with a Concrete Spreader
The Contractor must thoroughly moisten the base if there is no prime coat specified in the contract, prior to placing the CTFDB. Workers must not contaminate the CTFDB by walking through it with mud other foreign material on their work shoes.
The CTFDB must be spread in a smooth uniform layer prior to compacting it.
Inspection should include sampling the CTFDB mixture and testing for in place gradation after it is spread and before compaction. This testing is to be done in accordance with Supplement 1090.
Minimum temperature is required to be 35 ºF (2 ºC) and rising.
The material is not placed on frozen material or on rain softened subgrade or base.
Vibrating Plate behind Concrete Spreader
Steel Wheel Roller Compact the CTFDB
The CTFDB is to be shaped to produce a uniform density and cross-section. Compaction must not cause crushing of the aggregate particles.
The Contractor must make a minimum of two passes over any given area with the required steel wheel rollers.
Construction joints between each day’s work must be made by cutting transversely across the hardened CTFDB with diamond saws or the contractor is permitted to use forms to form the construction joints.
Curing CTFDB with 6-mil White Opaque Polyethylene Sheeting
Curing of CTFDB is to be done by placing 6-mil (150 μm) white opaque polyethylene sheets over the completed work. These coverings must be left in place for a minimum of three days. A cure day is defined as 24 consecutive hours of time in which the temperature is above 40 ºF (5 ºC). Add a cure day for each day the temperature falls below 40 ºF (5 ºC). Do not allow the use of liquid concrete curing membranes for curing.
Care must be exercised by the contractor so as to not damage any installed underdrains during placing or compacting of the CTFDB. The Contractor must ensure positive connection between the underdrain backfill and the CTFDB at all times during construction.
The Contractor is permitted to haul materials or operate equipment on completed CTFDB provided there is no significant displacement, breakup or contamination. If any of this occurs, the Contractor must stop using the completed CTFDB for such purposes until the Contractor can demonstrate to the Department that it will not happen again in the future. Any damage to the CTFDB must be corrected by the contractor at no cost to the State.
The Contractor must protect the completed CTFDB from contamination from fine material at all times.
The Contractor must use track mounted asphalt paving machines for placing the first lift of asphalt concrete on top of completed CTFDB. This first course must cure at a minimum over-night before placing succeeding lifts of asphalt concrete.
The compacted depth of the CTFDB is to be 4 inches (100 mm) with a tolerance of ±½ inch (13 mm). Depth checks must be made every 2000 square yards (1650 m²). Areas found to be out of this tolerance must be removed and replaced at no cost to the Department and retested for proper thickness.
The CTFDB must be constructed to the proper elevation and have the plan specified cross-slope. Checks should be made periodically to verify these parameters. The surface tolerance of the finished surface must not vary more than ½ inch from a 10 foot (13 mm from a 3 m) straightedge. Any irregularities exceeding this amount must be corrected by the Contractor.
The Contractor is required to place the next pavement layer on top of the CTFDB within 40 days from the end of the curing period. In addition, the Contractor must plan the work such that the CTFDB is completely covered with the next pavement layer and have the underdrain system in place and functioning by the end of the construction season in any calendar year.
The project will measure and calculate the area in square yards (square meters) based on the typical sections shown on the plans. Payment will be made at the contract bid price for work that is accepted in place.
2. Verify design
3. Proportioning and mixing as per 850.03.
4. Prime base or sprinkle base with water
5. Temperature must be above 35 °F (1.6 °C)
6. Use a spreader, if project quantity exceeds 5,000 square yards (4,000 square meters)
8. Check segregation and thickness.
9. Curing and protection.
10. Pay and measure according to 850.15 and 850.16.