So You Have a Slurry Seal Project

Just the basics: material calculation and field testing

Application Rate

Material Calculation

Extra Long Tons

Spread Rate

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 made up of 2,000 pounds of dry aggregate plus asphalt, accelerations or retardant, and water.

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

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).

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.

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

What’s the difference between a good slurry and bad slurry?

6 Months

Lance AllanPacific Emulsions, Inc.lance@raslurry.comwww.rubberslurry.com714-376-4852