513 FOAMED ASPHALT STABILIZED BASE COURSE
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Construct a Foamed Asphalt Stabilized Base Course (FASBC) using a mix consisting of a water-foamed performance-graded asphalt binder and an aggregate blend, as specified .
Foamed Asphalt Stabilized Base Course Section 926 Recycled Asphalt Pavement (RAP) 900.03 Reclaimed/Recycled Concrete (RC) 900.03 Aggregate Section 901 Portland Cement 902.03 Fly Ash 902.06.04 Performance Graded Asphalt Binders Section 904 Production Plants Section 915 Water 921.01 Lime 921.01
- 513.03.01 Mix Design. Refer to 904.04.03. Submit a mix design approval from MDOT SHA’s Office of Materials Technology’s (OMT) Soils and Aggregate Technology Division to the Engineer at least 30 days prior to placement of the FASBC material. Work will not be allowed to commence without OMT approval.
- 513.03.02 Quality Control Plan. Refer to 504.03, Section 915, and the following. Submit a Plant Quality Control Plan to the Office of Material Technology and a Field Quality Control Plan to the District Engineer’s representative for approval at least 30 days prior to the placement of any FASBC.
- (a) The Plant Quality Control Plan shall also contain the following:
- (1) Contact information and certifications for key personnel.
- (2) Laboratory location, equipment calibration information, and accreditations.
- (3) Plant calibration information.
- (4) Binder source.
- (5) Plant half-life and expansion ratio testing frequency.
- (6) Cleaning and maintenance schedule for plant foaming nozzles.
- (7) Construction method and historical composition of RAP, RC, and FASBC stockpiles.
- (8) Gradation, moisture, and temperature testing frequency of stockpiled materials.
- (9) Moisture control methods for stockpiles.
- (10) Mixture sampling and testing frequency for gradation, binder quantity, and moisture.
- (b) The Field Quality Control Plan shall contain the following, as a minimum:
- (1) Identification of production plants and their locations with respect to the project site.
- (2) Contact information and qualifications for key personnel.
- (3) Inspection and record keeping methods and minimum frequencies of sampling and testing.
- (4) Field density and thickness testing method and frequency.
- (5) Corrective actions that will be taken for unsatisfactory construction practices and deviations from the material Specifications.
- Maintain and make available upon request complete records of sampling, testing, corrective actions, and quality control inspections.
- 513.03.03 Mixing Plant. Refer to 915.04 and the following:
- (a) Capable of producing a homogeneous mix free from foamed asphalt globules and stringers.
- (b) Capable of mixing the RAP, RC, reclaimed aggregate material, aggregates, mineral filler, or any combination of the above, water, asphalt binder and additives meeting the approved job mix formula to form a homogenous mass that will bond together when compacted.
- (c) Equipped with an exterior test nozzle to verify proper foaming action and to provide a representative sample of the foamed asphalt.
- (d) Equipped with an internal electric heat cleaning system for self-cleaning foaming nozzles, or nozzles should be cleaned following accepted industry best practices. Diesel fuel shall not be used to clean foaming nozzles.
- 513.03.04 Equipment. Refer to 504.03.01.
- 513.03.05 Weather Restrictions
- (a) Temperature. A minimum surface temperature of 50 F and air temperature of 55 F are required during FASBC placement. Surface and air temperatures must be measured in the shade and away from artificial heat. Do not place FASBC when temperatures below 40 F are anticipated within the next 24 hours.
- (b) Precipitation. The existing aggregate base or subgrade must be dry at the time of placement. Do not begin placement when fog, showers, or rain are anticipated within 24 hours. When placement is ceased due to precipitation, all materials en route shall be wasted at no additional cost.
- 513.03.06 Storage and Transportation. FASBC must be stockpiled at the plant in a manner that prevents moisture changes. FASBC can be stockpiled for a maximum of seven days prior to placement, unless otherwise approved. Stockpiling is not permitted for mixes containing cement or Class C fly ash. Handle and transport FASBC in a manner that minimizes segregation and loss of moisture. Do not dump FASBC into piles, haul over the completed aggregate base course, or stockpile on the job site without approval.
- 513.03.07 Placement. All FASBC material is to be placed using pavers. If multiple lifts are to be placed, moisten the underlying surface prior to paving.
- 513.03.08 Compaction. Refer to 504.03.07. and as follows:
- (a) Measure in-place density by either MSMT 350 or MSMT 352 Method B. When MSMT 352 Method B is used, all nuclear density gauges used on the project shall be calibrated during placement of the control strip to the specific FASBC job mix formula, and the density gauge moisture content corrected for the presence of asphalt in the FASBC. Compacted dry density must be at least 97 percent of the maximum dry density and the compacted moisture content must be within two percentage points of optimum.
- (b) The initial moisture content correction for the nuclear gauge shall be based on the direct moisture content measurements made on the control strip. At the beginning of each day’s production, a moisture content specimen will be taken from the first load of delivered FASBC and sent to the laboratory for an overnight moisture content determination via a slow oven burn (temperatures less than 230 F). This moisture content will then be used to determine the density gauge moisture correction for the next day’s production.
- (c) Begin compaction operations, except on super elevated curves, at the sides of the course. Overlap the shoulder or berm at least 1 ft and progress toward the center parallel to the center line of the roadway. On super elevated curves, begin compaction at the low side and progress toward the high side. Continue compaction operations until all compaction marks are removed.
- 513.03.09 Curing and Maintenance. The FASBC shall be allowed to cure under ambient environmental conditions and must be successfully proof rolled as specified in Section 204 or a 20-ton loaded truck before overlaying, unless otherwise approved. Repair any damaged areas of the FASBC prior to overlaying as directed. Areas that cannot be repaired must be replaced for the full depth of the base. Only allow necessary construction traffic on the FASBC unless otherwise directed.
- Measure the FASBC mat moisture according to T 110, T 265 or D4643 content every 2500 lane ft through the full lift depth with a minimum sample weight of 3 lb daily until final cure is complete. Moisture may also be measured with a density gauge using the same method and locations used during compaction and applying asphalt and cement moisture corrections. Final cure will be considered complete when the moisture content drops at least 50 percent from the final compaction moisture and the FASBC is satisfactorily proof rolled as directed. Repair any damage to the completed FASBC material prior to overlaying as directed.
- 513.03.10 Sampling and Testing for Foamed Asphalt Cement Content. Sample for Asphalt Cement Content behind the paver using MSMT 457 sampling method A or B before compaction of the FASBC. Obtain a total of three random samples per placement day using the Random Sample Location program used in asphalt pavement core testing. A Contractor’s Certified Technician must sample the mixture at the project site as witnessed by the Administration.
- The Administration will test at least one of the random behind-the-paver mix samples according to T 308. The Administration will determine the added foamed asphalt content of the random sample(s) using the ignition oven correction factor and results previously developed from the approved bag samples. The average of the foamed asphalt content of the behind-the-paver samples must be within ± 0.4 of the Job Mix Formula’s foamed asphalt cement target but no less than two percent. If the average is not within ± 0.4 of the Job Mix Formula target, the FASBC must be removed and replaced at no additional cost.
- 513.03.11 Control Strip. Construct a control strip at an approved location to determine the roller patterns needed to achieve optimum density after compaction and after curing. Use the control strip to calibrate the nuclear density gauges used for QC and QA testing during placement. Place a minimum of 100 tons of FASBC in the control strip. The control strip shall be one-lane wide at the specified thickness and optimum foamed asphalt content.
- Measure in-place density and moisture content in the control strip at six random locations according to MSMT 350. The average compacted dry density must be at least 97 percent of the Proctor (AASHTO T 180D) maximum dry density and the average compacted water content must be within two percentage points of optimum. Moisture content must be measured at each location using either a slow oven burn, microwave drying, or other approved suitable means with the temperature not to exceed 110 F. The measured moisture content shall be used to determine the moisture offset for the density gauge to correct for the presence of asphalt in the FASBC. A successful proof roll of the control strip as specified in Section 204 or a 20-ton loaded truck and meeting the compaction requirements are needed before proceeding with remaining FASBC construction.
- Accepted control strips may remain in-place and will be accepted and measured as a part of the completed foamed stabilized base. Tests used for the test strip will not be included in the evaluation for payment. Should the removal of any control strip be necessary, the Contractor must remove it at no additional cost.
- The Administration reserves the right to collect additional samples and perform additional tests on the material from all FASBC areas for information purposes as directed. The results of these additional tests will not be used for acceptance or payment.
513.04 MEASUREMENT AND PAYMENT
- Foamed Asphalt Stabilized Base Course will be measured and paid for at the Contract unit price per square yard of the specified thickness. Surface area measurements will be based on the specified width of the base and the actual length measured along the centerline of the foamed asphalt stabilized base course. Payment will be full compensation for all aggregate, asphalt binder, other additives, furnishing, hauling, placing, curing, control strip, and for all material, labor, equipment, tools, and incidentals necessary to complete the work.
- Temporary graded aggregate base wedge constructed in conformance with Standard No. MD 104.01-28 will not be measured but the cost will be incidental to the foamed asphalt stabilized base course item. The cost of the Control Strip will not be measured but the cost will be incidental to the foamed asphalt stabilized base course item.