Special Provision

Warm Mix Asphalt (WMA)

1.0 Description

This is a specification intended for use in producing and placing Warm Mix Asphalt (WMA) with the use of a chemical additive on local and state roads

This work consists of an asphalt mixture composed of mineral aggregate, aggregate screening, asphalt binder, anti-stripping additive and/or warm mix additive (see approved warm mix additives below) mixed in an accepted asphalt hot mix plant. The mixtures will be produced in a SCDOT qualified asphalt plant that uses an additive listed on Qualified Product List No. 77 to produce Warm Mix Asphalt (WMA). All additives used for this type of technology must be accepted by the County prior to production and pre-qualified for use for this application.

The asphalt mixes must be placed on a prepared surface in accordance with this Special Provision, applicable SCDOT Supplemental Specifications, and applicable sections of the SCDOT Standard Specifications, other appropriate Special Provisions and in conformity with the plans. WMA will use the same acceptance criteria for conventional hot mix asphalt mixes.

Additives used in the production of the WMA may be pre-blended with the PG Binder at the asphalt terminal or introduced into the plant with other metering equipment as stated in section 2.4. PG binders that have chemical additives added at the terminal or at the asphalt plant must be heat and storage stable and continue to meet

AASHTO M 320

2.0 Materials

2.1 Aggregate

Ensure that aggregate used in the production of Warm Mix Asphalt (WMA) meet the requirements found in the current SCDOT Standard Specifications section 401.2.2 and in SC-M-407.

2.2 Asphalt Binder

Ensure that the binder is a neat asphalt binder that complied with the requirements of the SCDOT Standard Specifications section 401.2.1.1 using only PG64-22. Additives used in the production of the WMA may be pre-blended at the asphalt terminal or introduced into the plant with other metering equipment as stated in Section 2.4. PG binders that have chemical additives added at the terminal or at the asphalt plant must be heat and storage stable and continue to meet AASHTO M 320.

2.3 Anti-Strip Additives

Ensure anti-strip additives are used in all mixes except where the approved Warm Mix Technology serves dual purpose as described below in the WMA Additives Section. Hydrated Lime may be used as an alternative to chemical anti-strip additives.

If a LASA is used, ensure that the LASA is storage and heat stable and is compatible with the crude source of binder selected. Heat stable is defined as the product should be able to maintain its performance, as well as the binder grade, when held in hot asphalt cement at 350°F for one week.

Ensure that the LASA is added at the asphalt terminal at a minimum rate of 0.25%, or as determined to meet the requirements of 401.2.3.4 of the SCDOT Standard Specifications, by weight of the PG 64-22 asphalt binder regardless of mix type and the amount of recycled asphalt product. LASA’s that are blended at the terminal must be documented on the Bill of Lading (BOL) coming from the binder supplier. Ensure that the percent additive added to the PG 64-22 is printed on the BOL.

Ensure when hydrated lime is used that the lime meets the requirements of AASHTO M 303 Type 1 and that the hydrated lime is blended with the damp aggregate at a rate of 1.0% +/- 0.1% by weight of dry aggregate.

Ensure that the blending of the hydrated lime is accomplished according to subsection 401.2.1.3 of the SCDOT Standard Specifications.

2.4 WMA Additives

Ensure that mixtures use an additive listed on the SCDOT Qualified Product List No. 77 to produce Warm Mix Asphalt (WMA). All additives used for this type of technology must be accepted by the County prior to production and pre-qualified for use for this application.

For Warm Mix Additives that provide dual functionality as both an anti-strip additive and warm mix technology, provide laboratory data showing the mixture meets Section 401.2.3.4 of the SCDOT Standard Specifications. In addition, the Warm Mix Additive must be listed on both anti-strip and WMA qualified products lists.

Additives used in the production of the WMA may be pre-blended with the PG Binder at the asphalt terminal or introduced into the plant with other metering equipment as stated below.

Ensure that if the additive has been pre-blended at the asphalt terminal, it has been documented on the Bill of lading (BOL) coming from the binder supplier. Ensure that the percent additive added to the PG 64- 22 is printed on the BOL. Store the binder in a storage tank without any contamination from previous loads of virgin PG 64-22. label binder storage tanks noting the addition of WMA additives. All other WMA additives must be clearly identified at the asphalt plant and the WMA producer must have all documentation for the additives readily available for review at the asphalt plant.

Ensure that the WMA additive and or metering equipment manufacturer can provide technical assistance to the WMA producer by having a representative on site in the event of issues arising during use of the system within 24 hours of identifying problem.

Ensure that the additive metering equipment is tied into the computer in the plant control room so that metering of the non-terminally blended additives can be continuously monitored by the plant operator.

Ensure that metering systems can vary the amount of additives introduced into the asphalt plant and are automatically controlled by the plant production rate. Do not allow the WMA additive rate to go outside of the manufacturer's recommendations as stated in the WMA QC Plan, as stated in section 5. The recommendations should include a target dosage for the additives and upper and lower tolerance limits.

Ensure that if the additive equipment stops flow or if a control or equipment failure in occurs, the computer system immediately notifies the plant operator and all WMA production is stopped until the system is repaired and checked.

3.0 MIX DESIGN

Warm mix designs utilize the same asphalt binder grade, aggregate and RAP sources as identically-formulated hot mix asphalt (HMA). WMA mix designs utilizing additives will use asphalt that may be pre-blended from the asphalt terminal or may be introduced by adding the correct dosage of additives to establish mix design volumetric and drain down properties. Additional equipment may be required by the WMA additive manufacturer in the design process to ensure the proper dosage and to achieve a homogenous mixture. When the WMA additive also provides anti-stripping properties hydrated lime or additional liquid ASA are not required provided the mixture meets the requirements of 401.2.3.4. Additive manufacturers will provide documentation of proper mixing and compaction temperatures to produce and compact WMA mixtures. Ensure that WMA mixtures comply with SC-M-402.

Design WMA job mix formulas in accordance with SC-T-80. Ensure that all designs are accepted by Dorchester County and that mix designs are prepared in a laboratory approved by the SCDOT Asphalt Materials Manager and by technicians certified as a SCOOT Level 2, HMA Job Mix Technician

Heat and prepare the materials in a manner that produces a warm mixture that, when discharged, is at a mixture temperature that can be maintained from 220-285°F and provide a behind the screed temperature of no greater than 250°F. Use SC-T-84 to measure mix temperature at the asphalt plant and on the road in the delivery trucks.

4.0 FIELD REQUIREMENTS

Ensure that all WMA Systems or Additives used are listed on QPL No. 77. WMA additives are used to allow lower asphalt mix temperature. Use an additive that is compatible with the asphalt plant and acceptable to the County in producing WMA, and ensure that asphalt plant conforms to SC-M-401 after any modification. Ensure that the burner in the aggregate dryer is properly adjusted so that there is no burner fuel in the WMA.

Ensure that when any new metering equipment is installed on a contractor’s plant, that a trial run is done so all plant controls and metering equipment can be verified to be working accurately prior to production.

Ensure that all WMA mixtures are stored maximum of 8 hours in a separate storage silo from conventional HMA mixtures. Extended overnight storage of WMA mixtures will not be permitted.

Ensure that only one WMA additive is used during a day of production of WMA mixtures.

5.0 QUALITY CONTROL

Provide the County, prior to starting production, a QC Plan to document the manufacturer's suggestions for target production rates when using chemical additives, and produce an outline with acceptable variations at the asphalt plant and acknowledge that the mixture will remain within 220 °F - 285°F at all times and provide a maximum behind the screen temperature of 250°F.

When a contractor elects to plant blend the WMA chemical additives, the plan shall include daily plant print outs of the WMA additive dosage rates and these rates shall have been confirmed by manually measuring the additive used each day. Any WMA mix placed on a roadway not meeting the target WMA dosage rates shall be removed and replaced at the contractor’s expense.

Ensure that all WMA samples taken for field determination of binder content are dried to constant weight if necessary prior to running SC-T-75 as outlined in the WMAQC Plan.

When using Intermediate Type C, Surface Type B or Surface Type C mix types, perform Indirect Tensile Strength (ITS) testing using SC-T-70 at least one time during the first day's production, then at least once every 30 days thereafter. Compaction temperatures of the specimens should be +/- 15°F of the planned production temperature. Forward the results to the County immediately upon completion. Failure to comply with Section

401.2.3.4 of the standard specifications will cause the County to immediately suspend production. Redesign will be required for any job mix formula which fails to meet Tensile Strength Ratio (TSR) field requirements.

6.0 CONSTRUCTION

Ensure that ambient air temperatures and seasonal restrictions during placement of WMA follow the requirements set forth below:

Do not apply WMA when the existing surface is wet or frozen. Place WMA in accordance with the following table.

Lift Thickness (inches) Minimum Ambient Temperature (°F)*

1.0 or less 40.0 and rising

1.1 to 2.0 40.0 and rising

2.1 to 3.0 40.0 and rising

3.1 to 4.5 35.0 and rising

*Measure ambient air temperature in the shade with a calibrated thermometer away from artificial heat following SC-T-84.

7.0 FIELD ACCEPTANCE

During the production and quality control of WMA, make all necessary provisions to ensure that plant unit operations comply with SCDOT Specifications regarding the production of HMA as stipulated in Divisions 310 and Division 401 with exceptions as directed in this special provision.

8.0 MEASUREMENT

Measure and accept WMA mixtures by the ton or square yard placed.

9.0 PAYMENT

WMA Mixtures will be paid for at the contract unit price which will be for full compensation for furnishing all materials, equipment and labor.