SECTION 421
MICRO SURFACING
421.01 DESCRIPTION
This work consists of applying a thin overlay material composed of modified emulsified asphalt,
aggregate, water, and additives over a prepared surface.
421.02 EQUIPMENT
Equipment
Micro Surfacing Equipment
Section
156.02 D
Calibrate each mixing unit in the presence of the Engineer before starting work. Perform
calibration according to ISSA-MA 1. Include the individual calibration of each material at various
settings in the documentation.
421.03 MATERIALS
Item
Water
Aggregate
Bitumen
Section
812
816.04
818.03
A. Aggregates.
Screen the stockpile before delivery to the paving machine to prevent having oversize
material in the mix.
B. Mineral Fillers.
Use mineral filler to improve mixture consistency and to adjust mixture breaking and curing
properties. Use material that meets the requirements of ASTM D 242. Use levels of mineral
filler between 0.0 and 3.0 percent. Submit a certificate of compliance for the mineral filler.
C. Field Control Additives.
Use additives to accelerate or retard the break/set of the micro surfacing. The laboratory must
approve the appropriate additives and their application use range as part of the mix design.
Submit a certificate of compliance stating that the liquid field control additive is compatible with
the mix design.
421.04 CONSTRUCTION REQUIREMENTS
A. Mix Design.
Submit a mix design prepared by a qualified testing laboratory. Submit the certified test
reports with the mix design. Use the same materials in the mix design as on the project.
Obtain a new mix design from the same testing laboratory before changing any materials in
the mix design.
Submit a mix design conforming to Table 421-01.
Test
Mix Time @ 77°F
Table 421-01
Micro Surfacing Mix Design
ISSA
Specification
Test No.
Controllable to 120 Seconds
TB-113
Minimum
Wet Cohesion
@ 30 Minutes Minimum (Set)
TB-139
12 kg-cm Minimum
Wet Stripping
Wet-Track Abrasion Loss
TB-114
20 kg-cm or Near Spin
Minimum
Pass (90% Minimum)
One-hour Soak
TB-100
50 g/ft2 Maximum
@ 60 Minutes Minimum (Traffic)
Six-day Soak
Lateral Displacement
75 g/ft2 Maximum
5% Maximum
TB-147
Specific Gravity after 1,000 Cycles
of 125 lb
Excess Asphalt by LWT Sand
TB-109
Adhesion
2.10 Maximum
Classification Compatibility
11 Grade Points Minimum
(AAA, BAA)
TB-144
50 g/ft2 Maximum
Use component materials that meet requirements in Table 421-02.
Table 421-02
Micro Surfacing Component Material Requirements
Component
Quantity
Residual Asphalt
5.5% to 10.5% by dry weight of aggregate
Mineral Filler
0.0% to 3.0% by dry weight of aggregate
Polymer Content
Minimum 3.0% solids based on bitumen weight content
Additives
As required to provide specified properties
Water
As required to produce consistency
B. Test Strip.
Construct a one lane, 1,000 foot test strip for each machine used on the project at an
approved location within the project limits. Construct the test strip between 6:00 am and 9:00
am. Construct the test when the emulsion temperature is below 122°F.
Open the test strip to traffic within 90 minutes. The Engineer will inspect the test strip for
damage immediately after it begins carrying traffic. Begin full production only after the
Engineer accepts the test strip. If the test strip is unable to carry traffic after 90 minutes, modify
the material and placement and construct another test strip.
In place of construction of a test strip, submit evidence of successful construction of a test strip
on another Department project using the same mix designs. The project must have been
constructed in the same construction season. The material, material source, and equipment
used for the test strip must be identical to all parts of the proposed material, material source,
and equipment.
The Engineer may direct the construction of a new test strip during production application.
Construct a new test strip if the material or equipment changes.
C. Weather Limitations.
Place material when the surface and ambient temperatures are at least 45°F and the forecast
is greater than 32°F for 24 hours after placement. Do not place the material if the pavement or
ambient temperatures is below 50°F and falling.
Do not place the material if it is raining.
D. Traffic Control.
On two-lane, two-way traffic highways, place flaggers and signs at each end of the surfacing
operation and at major intersections within the operation area. On divided highways, place
flaggers and signs at major intersections within the micro surfacing area.
E. Surface Preparation.
Remove deleterious material.
Protect manholes, valve boxes and other service entrances from the surfacing material.
F. Application.
Fog the surface with water if necessary. Adjust the rate of application of the fog spray to suit
the pavement surface and atmospheric conditions. Do not allow water to pond on the surface.
Begin placement at the lowest point of the roadway cross section and place subsequent
passes upslope from the previous pass.
Uniformly spread the material using the spreader. Mix and spread a homogeneous material. If
material prematurely breaks before application, remove the material that broke prematurely
from the roadway and the spreader box.
Use hand methods to spread the mixture in areas inaccessible by mechanical spreaders.
Complete handwork at the time of the machine applied application. Finish hand-worked areas
to resemble the mechanical spreader finish.
If excessive streaking develops, stop production and fix the cause of the streaking. Streaking
is excessive if in any 30 square yard area there are more than four drag marks greater than:
 0.5 inches wide and 4.0 inches long; or
 1.0 inches wide and 3.0 inches long.
Construct joints with no excessive buildup or uncovered areas. Place longitudinal joints on
lane lines. Construct straight edges along curbs and shoulders and through intersections, with
no runoff.
Clean the spreader box to be free of material buildup at the start of each work day. Stop
operations and clean the spreader box if material buildup begins to affect performance.
421.05 METHOD OF MEASUREMENT
The Engineer will measure, completed and in place as specified in Section 109.01, “Measurement
of Quantities” and as follows.
The Engineer will measure the dry aggregate weight. The Engineer will subtract the weight of
moisture determined from moisture tests. The Engineer will determine the moisture content by
collecting 3 samples each day material is placed and averaging the moisture contents.
The Engineer will measure traffic control as specified in Section 704.05, “Method of
Measurement”.
421.06 BASIS OF PAYMENT
Pay Item
Aggregate for Microsurfacing Type_
Asphalt Emulsion for Microsurfacing
Pay Unit
Ton
Gallon
Such payment is full compensation for furnishing all materials, equipment, labor, and incidentals
to complete the work as specified.