This
item of work is used to provide a cold laid polymer modified emulsified asphalt
pavement course to fill ruts, depressions, and to provide a leveling
course. It can also be used as a surface
course over existing pavements. The
mixture includes the use of crushed aggregate, mineral filler, water, polymer modified emulsified asphalt binder, and other additives.
Materials
used in the mixture and the completed mix are approved by the Laboratory prior
to beginning work. The Contractor must
provide a certificate of analysis and statement of compliance from the
manufacturer with each load of binder.
Verify
job mix formula (JMF) approval by the Laboratory.
The
mixture cannot be placed when it is raining.
Allow
microsurfacing placement
if:
Mixing
equipment must conform to the specifications.
Equipment must be self-propelled, front feed, with a continuous loading conveyor system.
A gear pump must accurately proportion aggregate and asphalt
emulsion.
Mineral
filler must be dropped into the aggregate before reaching the pug mill. A spray bar must pre-wet the aggregate with
water and additive before the addition of asphalt emulsion and before it drops
into the pub mill.
The
pug mill must be continuous flow type and a minimum of 49 inches long.
The
equipment must have driving stations on both sides. The back mixing station must have forward
speed control to allow the mixing operator to control speed and the level of
mixture in the paver.
A
water pressure system with spray nozzles that can spray water ahead of the
spreader box may be required.
The
Contractor can use truck-mounted machines with a conveyor belt delivery system on project segments of less than 15,500 square yards or use it for spot repairs.
Figure 421.A –
Self-Propelled Front Feed, Continuous Loading and Mixing Machine (left)
Truck-Mounted Machine (right)
Before mix production,
calibrate the mixing equipment in the presence of the Engineer. Perform a new calibration
if there is any change in the mix design. Obtain documentation of individual
calibrations of each material from the equipment calibrator. After the initial calibration, no further
changes or adjustments to the mixing equipment can be made without the
Engineer’s approval.
The spreading equipment must
apply the mixture uniformly. A standard
spreader box is allowed when placing a leveling course or surface course. For surface courses, a secondary strike-off
must be attached to the spreader.
If a rut fill course is
required, the Contractor must use a V-shaped rut filling spreader box equipped
with a steel strike-off.
Either spreader box must be
attached to the mixer and must be equipped with adjustable paddles that
continuously agitate and mix the materials throughout the box. Check for excessive buildup and settling in
the spreader box and have the Contractor correct the issue.
Burlap or other drags are
allowed for use to provide the desired surface finish.
Be sure the surface is
thoroughly cleaned before application.
Apply a tack coat consisting of 1 part asphalt emulsion and 3 parts
water and apply at a rate of 0.06 to 0.12 gallons per square yard. Apply tack in accordance with 407.
Remove raised pavement
markers according to 621.08.
Fill depressions with the same material being used for the microsurfacing.
Pavement markings and all
other paint must be removed using an abrasion method.
A 1,000-foot test strip must
be constructed for evaluation by the Engineer.
The test must include all courses specified and must be constructed at
the same time of day as the scheduled, full-scale production. For example, if the Contractor plans night
work, the test strip must also be done at night.
The Engineer will evaluate
the test strip after 24 hours of traffic to determine if the mix design is
acceptable. Full-scale operations can
only begin after the Engineer accepts the test strip.
If work is scheduled after
May 1 and before September 30 and the Contractor has constructed a test strip
with the same JMF and materials in the same
construction season, the test strip may be waived.
During application the
following items should be closely checked and monitored:
Accept microsurfacing
based on the Engineer’s summary of quantities for each day provided the
proportion of binder to dry aggregate is maintained within 2 gallons per ton
(8.5 L/metric ton). Ensure all other control requirements for proportioning and
spread rate are in conformance with the specifications.
The final pavement surface
must be free from excessive scratch marks, tears, rippling, streaks, and other
surface discontinuities. Longitudinal
joints and transverse joints must be neat and straight.
Microsurfacing (surface and leveling course) is measured and paid by
the square yards completed and accepted.
The pavement width is as shown on the plans, specified in these
specifications, or as directed by the Engineer.
Length is measured along the centerline of the roadway.
Rut fill course will be
measured and paid by the number of tons of dry aggregate used and accepted
based on ticket weights.
The test strip will be paid
based on the acceptance at the individual bid prices for each course
placed. For example, if the plans
require a leveling and surface course, the test strip must be constructed using
these courses and would be paid on the measured quantities for both of these
items.
Tack coat is not paid
separately and is considered incidental to the work.
Figure 421.B – Unacceptable
Streaking (left); Unacceptable Surface Prep (right)
Figure 421.C – Unacceptable
Transverse Joint and “Skip”
Figure 421.D – Uniform
Coverage
1.
Check for
certificate of analysis and compliance from the manufacturer of the binder and
document for each load of binder.
2.
Check and
document surface preparation, pavement and atmospheric temperatures, and
forecast for next 24 hours.
3.
Verify and record
conformance to specifications for the mixing equipment.
4.
Verify that an
approved JMF is being used.
5.
Document
equipment calibration.
6.
Document
construction of test strip and the evaluation as well as any changes
implemented.
7.
Document surface
preparation and tack coat application.
8.
Document
placement operation regarding uniformity, rut filling, leveling, pounds per square yard used, construction of straight lines,
roller compaction (if required), issues, and corrections made.
9.
Document
acceptance, method of measurement, and calculations for pay.
10. Document on CA-D-3A
or other approved forms.