Total binder in SEAM mix = 10 000(4.6)1.7                             .
                           10 000(1.7)-(100)(40)(1.7-1) + 4.6(40)(1.7-1)
                           = 5.5% (total mix)

SEAM % = 5.5 x 0.4 = 2.2%

Asphalt cement % = 5.5 x 0.6 = 3.3%

The Marshall properties of this SEAM mix formulation may be verified using the procedure outlined below.

4.3 Alternatively, for a 5-point Marshall SEAM mix design, 5 binder contents (SEAM + Asphalt Cement) shall be selected with the 5 binder contents in the 40%SEAM / 60%Asphalt Cement weight ratio, and the usual Marshall design procedure shall be followed with the exception of the special provisions outlined below.

5. Special Provisions for the Marshall Design of SEAM Mixes

5.1 Determine the binder (SEAM + Asphalt cement) viscosity at two temperatures of 140 C and 115 C. The binder shall be prepared as follows. Place the asphalt cement and the SEAM in an oven set at 140 C. Blend the asphalt cement and the liquid SEAM together under a fume hood in a high shear blender (e.g. 20 000 rpm) and then measure the viscosity, preferably using a Brookfield viscometer. The blending time will depend upon blender efficiency. Allow the blend to cool to 115 C and reblend the binder for a short period of time while maintaining temperature and measure the viscosity. Plot a viscosity-temperature line for the binder.

5.2 Determination of Marshall mixing and compaction temperatures from 5.1: The temperature to which the binder must be heated to produce a viscosity of 170 20 cst shall be the mixing temperature and the compaction temperature shall be the temperature to which the binder must be heated to produce a viscosity of 280 30 cst. (Note: The mixing temperature shall not exceed 150 C.)

5. 3 SEAM mix preparation for Marshall design: A mechanical mixer must be used. Follow the usual procedures for aggregate and asphalt cement preparation for Marshall mix design and pre-weigh the amount of SEAM required. Add the SEAM pellets to the aggregate + asphalt mix after starting the mixer and then mix for the usual time period, e.g. 3 to 5 minutes. Compact the Marshall specimens as usual, at the temperature determined in 5.2.

5.4 Optimum binder content determination: Determine the optimum binder content (SEAM + Asphalt cement) as usual.

5.5 Marshall stability and flow: If the optimum binder content is not at one of the five binder contents selected in the design, then prepare an additional set of Marshall briquettes at the optimum binder content for testing after one day. Prepare a second set of Marshall specimens, allow them to age on the shelf, and test them after 14 days to determine SEAM mix long-term stability.

6. SEAM Mix Water Stripping Resistance

6.1 SEAM mix water stripping resistance, when using aggregates susceptible to stripping, shall be assessed using retained strength tests after specimen soaking such as the Marshall stability test or an indirect tensile strength test (e.g. AASHTO T283).

6.2 Liquid anti-strip agent shall be added to the asphalt oil prior to addition of SEAM in SEAM mixes which do not meet required minimum retained strength requirements, using anti-strip dosages recommended by the manufacturer. Hydrated lime shall not be used in SEAM mixes.

7. SEAM Mix Quality Control & Quality Assurance Testing

7.1 Marshall testing of plant production mix: Prepare specimens from the middle of a large plant mix sample at the compaction temperature determined in 5.2 in accordance with usually specified production requirements and test after one day. Avoid reheating SEAM mix. Periodically, prepare an extra set of specimens for testing after a 14 day aging period.

7.2 Control of binder content during SEAM mix production:

7.2.1 Determine the total binder content in the mix by burning off the binder (SEAM + asphalt) in an ignition oven.

7.2.2 Determine the asphalt cement content using the Troxler model 2226 asphalt content gauge, or an equivalent apparatus.

7.2.3 Determine the SEAM content by subtracting the asphalt content (7.2.2)

from the total binder content (7.2.1)

8. Physical Property Testing of SEAM Mixes

8.1 Time of testing: Physical properties of SEAM mixes such as rutting resistance, fatigue life, tensile strength, resilient modulus, etc. shall be carried out after the SEAM specimens have aged at ambient temperature for a minimum of 14 days.

8.2 Tests for SEAM evaluation: Theoretically based rational tests may be used for SEAM mix evaluation. Due to the unique structuring effect of SEAM on mix properties, empirical tests developed for conventional asphalt mixes shall not be used to test SEAM mixes unless they have been proven to reflect SEAM pavement performance.

8.3 SEAM mix rutting resistance at high temperatures shall be assessed using the Asphalt Pavement Analyzer (APA) or similar wheel tester and the test results shall comply with established criteria.

8.4 SEAM mix performance at low temperatures shall be assessed using AASHTO test method TP10-93: Method for Thermal Stress Restrained Specimen Tensile Strength and the test results shall comply with established criteria.

9. SEAM Mix Plant Production

9.1 Acceptable plant types: Both pugmill-mixer batch type as well as continuous drum-mix type asphalt plants may be used for SEAM mix production. It is preferable to add SEAM pellets using automated systems (e.g. cold bin with belt feeder or silo with screw auger feeder) either directly into the mixer of a batch plant or via the RAP collar in a drum-mix plant. SEAM shall not be exposed to high temperatures, significantly above 150 C, at the addition point in the mixer. This means that first generation drum-mix plant RAP feeders, which are designed to feed RAP into the very hot middle part of the drum shall not be used. To avoid exposure of SEAM to hot aggregate fresh from the dryer in batch plants, it is essential to maintain the hot bins at a minimum of two-thirds full during SEAM mix production.

9.2 SEAM mix production temperature: SEAM mixes shall be produced at a target temperature of 140 C. The maximum SEAM mix temperature allowed is 150 C. The installation of an infra-red temperature sensor is recommended for measuring SEAM mix production temperature.

9.3 SEAM mix rejection temperature at the plant: Delivery trucks containing SEAM mix shall be rejected when any one batch exceeds a temperature of 160 C or any two batches exceed a temperature of 155 C.

9.4 SEAM mix storage: It is recommended that SEAM mix storage time be kept to a minimum in order to minimize mix odor and fume emissions at the paving site.

9.5 SEAM mix rejection temperature at the paving site: Delayed delivery trucks arriving at the paving site with SEAM mix below a temperature of 115 C shall be rejected, measured at a depth of 15 cm in the load.

10. SEAM Mix Compaction

10.1 Breakdown rolling of SEAM mixes shall begin at the highest temperature possible without excessive shoving or rutting of the mix, with breakdown and intermediate rollers staying close to the paver. The use of rubber-tired rollers is discouraged with SEAM mixes due to a picking up of the fines and the ravaling of the mix due to this fine redistribution action that can occur prior to the finish rolling.

10.2 Final rolling shall be completed before the mix cools down to 70 C.

10.3 "Tender mixes" (i.e. densified mixes still subject to "movement" under roller pressure), shall be compacted as much as possible while hot in the 140 to 120 C temperature range but not disturbed in the 115 C to approximately 100 C range, with compaction continuing again starting at 100 C, when the mix can again support the weight of the roller.

10.4 Pavement density shall be measured using either a nuclear density gauge or from pavement cores. The usual pavement compaction standards shall apply for mixes with a SEAM/Asphalt cement ratio of 40/60 or lower. (For special mixes with a higher ratio, a lower density standard shall apply, based on US experience.)

Appendix 1

SEAM USE IN ASPHALT MIXES - SAFETY

Temperature Control

• SEAM mixes can be handled similar to conventional hot-mix with the exception of strict adherence to temperature control guidelines
• Emissions of hydrogen-sulphide, sulphur-dioxide, and sulphur vapor may be present during mix preparation. Concentration of these emissions is low or non-existent when SEA is produced using SEAM below 150 0C
• While SEAM has been formulated to minimize sulphur vapor, hydrogen-sulfide and sulphur odors, temperature control is the most important factor in the production of SEA for controlling sulphur emissions

Protective measures in H2S environments

• H2S will be non-detectable or below occupational exposure limits in work areas if SEAM mix processing temperature is maintained below 150 C
• For any processing vessels, stacks, pugmills, etc., any personnel entering must first monitor H2S before entering

Protection against irritants

• It is unlikely that the small amounts of H2S & SO2 would be of sufficient concentration to cause irritation in normal work areas
• Total dust and asphalt fumes and elemental sulphur dust may be in sufficient quantities to cause irritation. Irritant effects can be controlled by the use of the following protective devices:
  • Non-venting goggles
  • Disposable dust respirators

Health Standards

(Reference: American Conference of Governmental Industrial Hygienists, "2002 Threshold Limit Values for Chemical Substances and Physical Agents & Biological Exposure Indices." Source: www.acgih.org)

Notes:

1 Intended change to 5 ppm time-weighted average with no value for short-term exposure level.

2 Precipitated or sublimed sulphur is generally considered to be nontoxic for man and mammals when taken orally or applied to the skin. Sulphur aerosols may, however, cause eye irritation in human beings, being as low as 0.26 mg/m3

SEAM Handling

• SEAM may be stockpiled in bulk either indoors or outdoors on a clean base and is not affected by rain.
• SEAM is a manufactured in dustless pellet form and excessive handling should be avoided to minimize dust formation.
• At asphalt plants SEAM loaders should avoid pressing SEAM against a hard base to prevent dust formation and also because the pressure and scraping of metal on the base could cause sparking which could ignite the sulphur dust.

Extinguishing SEAM Fire

• Ignition of sulphur dust may cause slow, localized smoldering of the SEAM with a flame that is not readily visible but noticeable by SO2 odor emission.
• The standard procedure for extinguishing a sulphur dust fire is to smother it by shoveling more SEAM onto it to exclude air and to extinguish the flame (Ref. National Fire Protection Assoc., Boston, Mass.)
• Water is the most satisfactory extinguishing agent and carbon dioxide fire extinguishers may also be used. (Ref. Chemical Safety Data Sheet SD-74, Manufacturing Chemists Assoc., Washington, D.C.)
• If SEAM is stored in bulk indoors, automatic sprinkler systems are recommended in enclosures in which SEAM is stored (Ref. National Fire Protection Assoc., Boston, Mass.)