so you have a slurry seal project just the basics: material calculation and field testing
TRANSCRIPT
So You Have a Slurry Seal Project
Just the basics: material calculation and field testing
Application
Rate
Material Calculation
Extra Long Tons
Spread
Rate
Wet Ton
Aggregate Application Rate
Material Calculation
Aggregate Type Application Rate
MINIMUM (Thinner, Lighter) MAXIMUM (Thicker, Heavier)
Type I 8 lbs/yd2 10 lbs/yd2
Type II 12 lbs/yd2 15 lbs/yd2
Type III 20 lbs/yd2 25 lbs/yd2
Application Rate
Used in 2012 Greenbook
Easy round numbers for calculations
Easy to visualize that a lower number means a thinner/lighter application and a higher number is a thicker/heavier application rate
Streets are more often measured in Square Feet
Aggregate is most often measured in Tons
Converting between to two can lead to mistakes
Aggregate Spread Rate
Material Calculation
Aggregate Type Area Covered
MINIMUM (Thicker, Heavier) MAXIMUM (Thinner, Lighter)
Type I 1800 ft2/ELT 2200 ft2/ELT
Type II 1200 ft2/ELT 1500 ft2/ELT
Type III 900 ft2/ELT 1125 ft2/ELT
Spread Rate
Used in Greenbook prior to 2012 and still very commonly used in the field
Uses units more commonly used for measuring streets, square feet, and aggregate, tons.
More difficult to visualize that a lower number means a heavier application rate
Extra Long Ton (ELT)
Material Calculation
An extra long ton of slurry is measured by 2,000 pounds of dry aggregate. The weight of the asphalt emulsion, additives, and water is not included in the measurement.
What this means is that we are only concerned with the weight of the aggregate in the slurry. The terms Tons and ELT are often used interchangeably when referring to slurry.
Extra Long Ton
Once understood it simplifies measuring slurry seal material quantities.
It gives the agency a verifiable way to measure slurry seal material quantities with aggregate delivery tickets.
Still the most common unit to describe slurry seal material
Can be difficult to understand, and was made confusing by an error in a past Greenbook when converting to Tonnes
No longer mentioned 2012 Greenbook
Wet Ton
Material Calculation
An wet ton of slurry is measured by 2,000 pounds of dry aggregate and asphalt emulsion, the weight of the additives and water are not included in the measurement.
What this means is you must add the weight of the aggregate AND the emulsion to calculate a ton of slurry.
Wet Ton
It ensure the monitoring of both the aggregate and the emulsion on a project.
While the Wet Ton is common on Caltrans projects, the Extra Long Ton is still the predominate method used to calculate slurry seal.
It can complicate determining quantities by the engineer because spread rates are calculated based upon aggregate only.
Emulsion percentages can vary, which will again affect slurry seal quantities.
Examples
Material Calculation
1) 2,000,000 square feet of streets to slurry with Type II, how many tons of slurry will you need?
a) Type II slurry has a spread rate of 1200SF/Ton to 1500SF/Ton, or an average of 1350 SF.
b) 2,000,000SF / 1350 = 1481 tons of slurry.
2) A contractor used 650 Tons of Type II aggregate to cover 1,000,000SF of streets. Was this a thick or a thin application?
a) 1,000,000SF / 650 Tons = 1538 SF/Tonb) Spread rate is 1200SF/Ton to 1500SF/Tonc) Higher spread rate is thinner, this is a thin slurry (actually out of spec).
Examples
Material Calculation
3) A job is bid for 2000 Wet Tons of type II slurry seal, how much aggregate and emulsion should be used on the project?
a. At 16% Emulsion solve for aggregateb. .16x+x=2000c. 1.16x=2000d. x=2000/1.16e. x=1724 (aggregate tons)f. Emulsion = .16*1724 = 276g. 1724(aggregate) + 276 (emulsion) = 2000 Wet Tons of Slurry Seal
Engineer Tips:
Material Calculation
1) Bid by area or weight?a) Area
i) Pro - Bidding by area is the simplest way to measure slurry seal.ii) Con - You most likely will the minimum application rate.
b) Weighti) Pro - You know you are getting the material you are paying for, and the street
will most likely receive a heavier application of slurry seal. ii) Con - Calculating and keeping track of the quantities is more difficult.
2) Application rates are controlled both by the contractor and the surface the slurry is being applied to.
a) Coarse street and first application of slurry seal = heavier application rate.b) Street with multiple slurry seal applications = lighter application rate.c) Cape Seal/Chip Seal, slurry seal may have to be applied heavier than normal
application rate to cover chip.
Inspector Tips:
Material Calculation
1) You should collect material weight tickets daily.a) Both aggregate and emulsion
2) You should calculate square feet covered daily.3) Estimate the remaining material left in the stockpile.
With this information you can estimate the spread/application rates, if the job is going to be over or under quantity, calculate progress payments, etc.
Material quantities can also be estimated by slurry machine calibration numbers, but this is not a replacement for material delivery tickets or visually verifying material in the stockpile.
Water ContentExtraction Test
Consistency TestWet Track Abrasion Test (WTAT)
Slurry Seal Field Tests
Field sampling methods and conditions have a strong effect on field test results. These tests where designed to be performed in a lab on lab prepared samples. Because of this there should always be some reservation when presented with failing results from field samples. More testing may be necessary as well as visually verifying that the test results are representative of how the material is actually performing.
Because slurry can segregate easily, it is important to take a sample from a location where all the components of the slurry are in suspension. The most common way is to take a sample from chute on the slurry seal machine. The difficulty in this is that the slurry seal machine is moving and the material exits the chute with great force.
Test results should always be confirmed by comparing them to the actual quantities of materials being delivered and used.
Slurry Seal Sampling
Water ContentPurpose - To determine if amount of water in the slurry seal is below the maximum allowed.
a) Too much water can cause a slurry to segregate, the aggregate falls to the bottom and the emulsion rises to the top. This results in a slick slurry.
b) Too much water can prevent proper bonding of asphalt and aggregate.c) An overly wet mix will often produce a thin application rate.
Sample of slurry seal should be retained in a way that moisture will not escape the sample. Quart sample jars with screw top lids are often used.
Extraction TestPurpose - To determine the asphalt percentage of the cured slurry seal as well as the calculated emulsion content.
a) Too much asphalt/emulsion may result in a slick slurry that may push and shove.b) Too little asphalt/emulsion may result in a slurry that wears prematurely.
Consistency TestPurpose - To ensure the slurry mixture remains homogeneous, does not separate, and is not
too ‘wet’. Below is a good example of how the consistency should look.
Wet Track Abrasion Test (WTAT)
Purpose - To test accelerated wear on a slurry seal sample.
Results can be highly impacted by the preparation of the sample. The sample should be collected in a shallow container and/or stirred to prevent segregation of materials. The sample should be quickly spread with only one or two passes of the squeegee. A separate sample of material should be obtained for each wet track patty.
The components of a quality slurry seal project:
1)Quality Specifications2)Quality Contractor3)Quality Material4)Quality Inspection
References
Slurry Systems Inspector’s ManualAvailable from:
International Slurry Surfacing Association3 Church Circle, PMB 250Annapolis, MD 21401Tel +1 410 267-0023Fax +1 410 267-7546
References
Slurry Seal Application ChecklistAvailable from the FHWA website:
http://www.fhwa.dot.gov/pavement/preservation/ppcl13.cfm
