Transcript So You Have a Slurry Seal Project - California Chip Seal Association

So You Have a Slurry
Seal Project
Just the basics: material calculation and field testing
Material Calculation
Material Calculation
Aggregate Application Rate
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
Streets are more often measured in
Square Feet
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
Aggregate is most often measured in
Tons
Converting between to two can lead
to mistakes
Material Calculation
Aggregate Spread Rate
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
Material Calculation
Extra Long Ton (ELT)
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
Material Calculation
Wet Ton
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.
Material Calculation
Examples
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.
1) A contractor used 650 Tons of Type II aggregate to cover 1,000,000SF of
Was this a thick or a thin application?
streets.
a) 1,000,000SF / 650 Tons = 1538 SF/Ton
b) Spread rate is 1200SF/Ton to 1500SF/Ton
c) Higher spread rate is thinner, this is a thin slurry (actually out of spec).
Material Calculation
Examples
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 aggregate
b. .16x+x=2000
c. 1.16x=2000
d. x=2000/1.16
e. x=1724 (aggregate tons)
f. Emulsion = .16*1724 = 276
g. 1724(aggregate) + 276 (emulsion) = 2000 Wet Tons of Slurry Seal
3)
Material Calculation
Engineer Tips:
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) Weight
i) 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.
Material Calculation
Inspector Tips:
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.
Slurry Seal Field Tests
Water Content
Extraction Test
Consistency Test
Wet Track Abrasion Test (WTAT)
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.
Slurry Seal Sampling
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.
Water Content
Purpose - 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 Test
Purpose - 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 Test
Purpose - 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
2) Quality
3) Quality
4) Quality
Specifications
Contractor
Material
Inspection
References
Slurry Systems Inspector’s Manual
Available from:
International Slurry Surfacing
Association
3 Church Circle, PMB 250
Annapolis, MD 21401
Tel +1 410 267-0023
Fax +1 410 267-7546
References
Slurry Seal Application Checklist
Available from the FHWA website:
http://www.fhwa.dot.gov/pavement/pres
ervation/ppcl13.cfm
So You Have a Slurry Seal
Project
Lance Allan
Pacific Emulsions, Inc.
[email protected]
www.rubberslurry.com
714-376-4852