ITEM 421 MICROSURFACING
421.01
Description
421.02
Materials
421.03
Proportioning
421.04 Weather Limitations
421.05 Mixing
Equipment
421.06
Equipment Calibration
421.07
Spreading Equipment
421.08 Surface
Preparation
421.09 Test
Strip
421.10
Application
421.11
Acceptance
421.12 Method
of Measurement
421.13 Basis of
Payment
421.01 Description. This work consists of
constructing a cold laid polymer modified emulsified asphalt pavement course to
fill ruts or provide a leveling and/or surface course for existing
pavements. The paving mixture is composed of a polymer modified
emulsified asphalt binder, crushed aggregate, mineral filler, water, and other
additives.
421.02 Materials. Use a polymer modified emulsified
asphalt binder (Binder) consisting of the following materials milled together:
A. Natural SBR
latex modifier or synthetic SBR latex modifier
conforming to 702.14. Use only one type
of latex.
B. CSS-1h or CSS-1m (as required below) emulsified
asphalt conforming to 702.04, except the
cement-mixing test is waived. Use only emulsion certified according to
Supplement 1032.
Use
CSS-1mL (as defined below) if the project ADTT is
less than 2000, otherwise use CSS-1hL (as defined below). Do not use port
addition of the polymer to the emulsified asphalt. Provide to the Engineer
certified test data and a statement from the Binder manufacturer with each load
of Binder that the Binder is the same formulation as used in the mix design.
Ensure the Binder meets one of the following:
CSS-1hL:
Combine CSS-1h and SBR latex modified (L) to yield 3
percent SBR solids based on the weight of the asphalt
binder content of the Binder. Ensure that the SBR
latex modified residue conforms to the following requirements:
Test |
Description |
Specification |
Residue by Evaporation |
62 % |
|
Softening Point |
60 °C minimum |
|
Absolute Viscosity @ 60 °C |
8000 poise minimum |
CSS-1mL:
Combine CSS-1m and SBR latex modifier (L) to meet the
following properties.
Tests on emulsion, ASTM D 244, unless otherwise designated: |
|
Viscosity, Saybolt Furol, ASTM
D 88, at 25 °C (sec) |
20 to 100 |
Storage Stability Tests, 24-hr (% difference) |
1 maximum |
Particle Charge Tests |
Positive |
Sieve Tests (%) (Distilled Water) |
0.10 maximum |
Distillation to 260 °C, % by Weight, Residue, min[1] |
62 |
Tests on distillation residue: |
|
Penetration, 25 °C, 100 g, 5 sec (dmm)
ASTM D 5 |
70 to 90 |
Ductility, 4 °C, 5 cm/min, ASTM D 113 |
40 minimum |
Elastic Recovery, 4 °C, 10 cm (%)[2] |
65 minimum |
Softening Point, Ring & Ball (°C) ASTM D 36 |
60 minimum |
[1] ASTM
D 244, with modifications to include a 400 °F ± 10 °F (204 °C ± 6
°C) maximum temperature to be held for 15 minutes. [2] Straight molds. Hold at test temperature
for 90 minutes. Place in ductilometer and elongate
10 cm at 5 cm/min. Hold for 5 minutes and cut. After 1 hour retract the
broken ends to touch and measure the elongation (X) in centimeters. Use the
following formula to calculate the elastic recovery: |
Conform
to 703.01 and 703.05 for aggregate, except as follows:
Percent by weight of fractured pieces |
100 |
Sand Equivalence (ASTM D 2419) |
45 minimum |
Conform
to Gradation A for the aggregate for leveling and surface courses and to
Gradation B for the aggregate for rut fill courses according to the following:
Sieve Size |
|
Total Percent Passing |
|
|
A |
B |
|
3/8 inch |
(9.50 mm) |
100 |
100 |
No. 4 |
(4.75 mm) |
85 to 100 |
70 to 90 |
No. 8 |
(2.36 mm) |
50 to 80 |
45 to 70 |
No. 16 |
(1.18 mm) |
40 to 65 |
28 to 50 |
No. 30 |
(600 µm) |
25 to 45 |
19 to 34 |
No. 50 |
(300 µm) |
13 to 25 |
12 to 25 |
No. 100 |
(150 µm) |
– |
7 to 18 |
No. 200 |
(75 µm) |
5 to 15 |
5 to 18 |
Screen
the aggregate for oversize material prior to use. For mineral filler, use
Portland cement conforming to ASTM
C 150, Type I. Use water conforming to 499.02.
Use mix set additives as required.
421.03 Proportioning. Submit to the Laboratory a
sample of the Binder to be used and a complete mix design prepared by an
approved laboratory. Verify the compatibility of the aggregate, Binder, mineral
filler, and other additives. Make the mix design with the same materials
that will be used on the project.
Ensure
that the mix design:
A.
Has aggregate meeting the gradation specified.
B.
Has residual asphalt by dry weight of aggregate of 7.0 to 8.5 percent for
leveling and surface courses or 6.5 to 8.0 percent for rut fill courses.
C.
Has a mineral filler content of 0.25 to 3.5 percent by dry weight of aggregate.
D.
Meets the specified properties of the following International Slurry Seal
Association (ISSA) tests:
ISSA Test No. |
Description |
Specification |
TB-139
(1-90) |
Wet Cohesion |
|
30 minutes min. (set time) |
12 kg-cm min. |
|
60 minutes min. (traffic) |
20 kg-cm min or near spin |
|
TB-114
(1-90) |
Wet Stripping |
90 percent min. |
TB-100
(90) |
Wet Track Abrasion Loss 1-hour soak 6 day soak |
450 g/m² max. 650 g/m² max. |
TB-144
(2-89) |
Saturated Abrasion Compatibility |
3 g loss max. |
TB-113
(1-90) |
Mix Time @ 25 °C |
Controllable to 120 seconds |
Mix Time @ 40 °C |
Controllable to 35 seconds |
Check
the ISSA TB-139 (set time) and ISSA TB-113 (mix time) tests at the highest temperature
expected during construction. For the ISSA TB-113 test at 104 °F (40 °C), preheat all
ingredients and containers.
Ensure
that the final mix design states the following (all percentages are based on
the dry weight of the aggregate):
A.
Source of each individual material.
B.
Aggregate gradation.
C.
Percentage of aggregate.
D.
Sand equivalence of the aggregate.
E.
Percentage of mineral filler (minimum and maximum).
F.
Percentage of water (minimum and maximum).
G.
Percentage of mix set additives (if required).
H.
Percentage of Binder and type.
I.
Quantitative effects of moisture content on the unit weight of the aggregate.
421.04 Weather Limitations. Apply the
mixture only when it is not raining and the existing pavement surface
temperature is a minimum of 40 °F (5 °C) and there is no forecast of an
atmospheric temperature below 32 °F (0 °C) within 24 hours from the time the
mixture is applied. Between September 30 and May 1, do not apply the
mixture if the existing pavement surface temperature is less than 50 °F (10
°C).
421.05 Mixing Equipment. Produce
the mixture in a self-propelled, front feed, continuous loading mixing machine
equipped with a conveyer belt aggregate delivery system and an interconnected
positive displacement, water jacketed gear pump to accurately proportion
aggregate and asphalt emulsion. Locate the mineral filler feed so the
proper amount of mineral filler is dropped on the aggregate before discharge
into the pugmill. Provide a spray bar to
completely prewet the aggregate dropping down to the pugmill with additive and water before introduction of
asphalt emulsion. The twin-shaft, multi-blade pugmill
will be a continuous flow type and minimum of 49 inches (1.25 m) long.
Ensure that the blade size and side clearances meet the equipment
manufacturer’s recommendations. Introduce the emulsion within the first
one-third of the mixer length to ensure proper mixing of all materials before
exit from the pugmill.
Equip
the machine with opposite side driving stations to allow full control of the
machine from either side. Equip the mixer with a remote forward speed control
at the back mixing platform so the back operator can control forward speed and
level of mixture in the paving or rut box. Provide material control
devices that are readily accessible and positioned so the amount of each
material used can be determined at any time.
Equip
the mixing machine with a water pressure system and nozzle type spray bar to
provide a water spray ahead of and outside the spreader box when
required. Apply water at a rate that will dampen the surface, but will
not create free flowing water ahead of the spreader box.
The
Contractor may use truck-mounted machines with a conveyer belt aggregate
delivery system and without the front feed, continuous loading feature on
project segments of less than 15,500 square yards (13,000 m2) or on
spot repairs.
421.06 Equipment Calibration. Before
mix production, calibrate the mixing equipment in the presence of the
Engineer. Generate documentation for the Engineer, including individual
calibrations of each material at various settings. Perform a new
calibration if there is any change in the mix design. Supply all of the
equipment, materials, and scales necessary to perform the calibration.
Following calibration and adjustments for changes in the mix design do not make
any further calibration adjustments to the mixing equipment without the
Engineer’s approval.
421.07 Spreading Equipment. If a
leveling or surface course is specified, apply the mixture uniformly by means
of a conventional spreader box.
If
a rut fill course is specified, apply the mixture with a V-shaped rut filling
spreader box. Equip the rut filling spreader box with a steel strike-off.
Attach
either type of spreader box to the mixer and equip it with paddles mounted on
an adjustable shaft to continually agitate and distribute the materials
throughout the box. Ensure that the equipment provides sufficient
turbulence to prevent the mix from setting in the box or causing excessive side
build-up or lumps. To prevent loss of the mixture from the box, attach
flexible seals, front and rear, in contact with the road. Operate the
spreading equipment in such a manner as to prevent the loss of the mixture on superelevated curves.
For
surface courses, attach a secondary strike-off to the spreader.
The
Contractor may use burlap drags or other drags, if necessary, to obtain the
desired finish. Replace drags having excessive build-up.
421.08 Surface Preparation. Before
applying the mixture, thoroughly clean the surface.
Apply
a tack coat conforming to Item 407, consisting of one
part asphalt emulsion and three parts water. Apply the tack coat at a
rate of 0.06 to 0.12 gallon per square yard (0.25 to 0.45 L/m²).
Remove
raised pavement markers according to 621.08.
The Contractor may fill the depression caused by the removal of the casting
with material meeting this specification.
Remove any existing longitudinal pavement
markings 740.03 (polyester), 740.04 (thermoplastic) and 740.07(epoxy) using an abrasion method
conforming to 641.10. Protect
drainage structures, monument boxes, water valve, etc. during material
application.
421.09 Test Strip. Construct a test strip for the
Engineer to evaluate. Construct this test strip 1000 feet (300 m) long,
and include all of the application courses specified. Construct the test
strip at the same time of day or night the full production will be
applied. The Contractor may construct the test strip in 2 days or nights
if multiple course applications are specified.
The
Engineer will evaluate the completed test strip after 24 hours of traffic to
determine if the mix design is acceptable. The Contractor may begin full
production after the Engineer accepts the test strip.
If
the microsurfacing is not being applied between
September 30 and May 1, the Department will waive the test strip if the
Contractor has constructed a Department approved test strip this construction
season with the same materials and mix design.
421.10 Application. Apply the paving mixture
in a manner to fill cracks, shallow potholes, and minor surface irregularities
and achieve a uniform surface without causing skips, lumps, or tears.
Carry a sufficient amount of material at all times in all parts of the spreader
box to ensure complete coverage. Avoid overloading of the spreader
box. Do not allow lumping, balling, or unmixed aggregate in the spreader
box.
If
a rut fill course is specified, apply enough material to fill the wheel paths
without excess crowning (overfilling). An excess crown is defined as 1/8
inch (3 mm) after 24 hours of traffic compaction. Apply rut fill courses
in widths from 5 to 6 feet (1.5 to 1.8 m) for each wheel path. Provide a
smooth, neat seam where two rut fill passes meet. Take care to restore
the designed profile of the pavement cross-section. Feather the edges of
the rut fill course to minimize the use of excess material.
If
a leveling course is specified, apply the paving mixture at 14 ± 2 pounds per
square yard (7.6 ±1.1 kg/m²).
If
a surface course is specified and it is placed on another microsurfacing
course, apply the paving mixture at 16 ±1 pounds per square yard (8.7 ±0.6
kg/m²). If a surface course is specified and it is not placed on another microsurfacing course, apply the paving mixture at a
minimum of 18 pounds per square yard (9.8 kg/m²).
For
leveling and surface courses, provide a smooth, neat seam of 1 to 3 inches (25
to 75 mm) where two passes meet. Immediately remove excess material from
the ends of each run.
Construct
surface courses wide enough to cover the outside edges of rut fill and leveling
courses. Maintain straight edge lines along curbs and shoulders. Do
not allow runoff of these areas. Ensure that lines at intersections are
straight.
Use
squeegees and lutes to spread the mixture in areas inaccessible to the spreader
box and areas requiring hand spreading. The Contractor may adjust the mix
set additive to provide a slower setting time if hand spreading is
needed. Do not adjust the water content to adjust the setting time.
If hand spreading, pour the mixture in a small windrow along one edge of the
surface to be covered and spread it uniformly by a hand squeegee or lute.
Ensure
that the microsurfacing cures at a rate that will
permit traffic on the pavement within 1 hour after application without damaging
the pavement surface. However, should the contractor have concerns about
adequate cure, work out an arrangement agreeable to the project before
releasing traffic on the pavement.
If
there is an excessive streaking problem created by high amounts of oversize
material in the mix, stop applying the mixture and take steps to correct the
streaking problem. Do not resume work until the Engineer is satisfied the
problem has been corrected.
If
a section of pavement is not going to be exposed to traffic within 48 hours,
compact it with a pneumatic tire roller after curing. Conform the
pneumatic tire roller to 401.13, and inflate the
tire pressure to 40 to 60 pounds per square inch (275 to 400 kPa).
421.11 Acceptance. Maintain continuous control of
the binder to dry aggregate proportioning to conform to the approved mix design
within a tolerance of ±2 gallons per ton (±8.5 L/metric ton). Control the
spread rate to not less than the specified quantity of aggregate per square
yard (square meter) on a dry weight basis.
The
Engineer will base acceptance of the Binder to dry aggregate proportion and
spread rate on the Engineer’s summary of quantities used each day. The
Engineer will approve and accept a day’s application of microsurfacing
provided:
A.
The Engineer’s summary indicates conformance with the above control
requirements for proportioning and spread rate and
B.
The pavement is free from excessive scratch marks, tears, rippling and other
surface irregularities, longitudinal joints and lane edges coincide with any
lane lines and edge lines and transverse joints are uniform, neat and provide a
smooth transition.
The
spread rate requirement does not apply to rut fill courses if the Contractor
filled the wheel paths according to this specification.
421.12 Method of Measurement. The
Department will measure Microsurfacing, Surface
Course and Microsurfacing, Leveling Course by the
number of square yards (square meters), complete and accepted in place.
The Department will base the width of the pavement course on the width shown on
the plans, specified in this specification, or directed by the Engineer.
The Department will measure the length along the centerline of each roadway or
ramp.
The
Department will measure the number of raised pavement markers removed.
The
Department will measure Microsurfacing, Rut Fill
Course by the number of tons (metric tons) of dry aggregate used, complete and
accepted in place. The Department will base the weight of the dry
aggregate used on the ticket net weight of individual loads from an approved
scale.
421.13 Basis of Payment. The cost
of tack coat is incidental to Microsurfacing.
The
cost of any removal of any existing longitudinal pavement markings according to
421.08 is incidental to Microsurfacing.
The
Department will pay for removal of existing raised pavement markers according
to Item 621 Raised Pavement Markers Removed.
The
Department will pay for the construction of accepted test strips at the
individual bid prices for the courses constructed.
The
Department will pay for accepted quantities at the contract prices as follows:
Item
Unit
Description
421
Square
Yard
Microsurfacing, Surface Course
(Square Meter)
421
Square
Yard
Microsurfacing, Leveling Course
(Square Meter)
421
Ton
Microsurfacing, Rut Fill Course
(Metric Ton)