MICRO SURFACING
PART 1 GENERAL
1.1SECTION INCLUDES
A.Products and procedures for mixing and spreading a properly
proportioned homogeneous mixture of aggregate, mineral filler, additives, polymer-modified asphalt emulsion and water to an existing pavement providing a firm surface adhesion and smooth, stable, and skid-resistant texture.
1.2RELATED SECTIONS
A.Section 02701: Pavement Smoothness
B.Section 02742S: Project Specific Surfacing Requirements
C.Section 02746: Hydrated Lime
1.3REFERENCES
A.AASHTO M 17: Mineral Filler for Bituminous Paving Mixtures
B.AASHTO M 85: Portland Cement
C.AASHTO T 11: Materials Finer Than 75 µm (No. 200) Sieve in Mineral
Aggregate by Washing
D.AASHTO T 27: Sieve Analysis of Fine and Coarse Aggregates
E.AASHTO T 49: Penetration of Bituminous Materials
F.AASHTO T 53: Softening Point of Bitumen (Ring-and-Ball Apparatus)
G.AASHTO T 59: Emulsified Asphalts
H.AASHTO T 96: Resistance to Degradation of Small-Size Coarse
Aggregate by Abrasion and Impact in the Los Angeles Machine
I.AASHTO T 104: Soundness of Aggregate by Use of Sodium Sulfate or
Magnesium Sulfate Micro Surfacing
J.AASHTO T 112: Clay Lumps and Friable Particles in Aggregate
K.AASHTO T 176: Plastic Fines in Graded Aggregates and Soils by Use of
the Sand Equivalent Test
L.AASHTO T 278: Surface Frictional Properties Using the British Pendulum
Tester
M.AASHTO T 279: Accelerated Polishing of Aggregates Using the British
Wheel
N.ASTM D 6372: Design, Testing, and Construction of Microsurfacing
O.International Slurry Seal Association (ISSA) Specifications and Guidelines
P.UDOT Minimum Sampling and Testing Requirements
Q.UDOT Quality Management Plans
1.4DEFINITIONS
A.Emulsified Asphalt - The emulsion.
B.Emulsified Asphalt Residue - The residue of the emulsion.
C.Residual Asphalt - The residue of the mixture.
D.Lot – One day’s production.
1.5SUBMITTALS
A.Provide the mix design for approval before beginning construction.
1.Refer to this Section, Article 2.6.
2.The mix design must be performed by an AASHTO Resource
accredited laboratory experienced in the design of micro surfacing systems.
3.Provide the Engineer with the following for polymer-modified
asphalt emulsion with job-mix design.
a.Test report that meets the requirements of this Section,
Article 2.1.
b.Target gradation for combined aggregate, and for mineral
filler.
c.Name of the asphalt emulsion supplier.
d.Verification that the emulsion supplier adheres to UDOT
Quality Management Plan Section 508, Asphalt Emulsion.
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B.Provide test reports for mineral aggregate for information.
1.Refer to this Section, Article 2.2.
C.Provide a Manufacturer’s Certificate of Compliance for the Mineral Filler
for information.
1.Refer to this Section, Article 2.3.
D.Provide calibration documentation for each mixing unit, including an
individual calibration for each material at various settings that corresponds to the mixing unit metering device for information.
E.Changes in the job-mix gradation for approval.
1.Submit a written request for any change in the job-mix gradation.
2.Submit a new job-mix design if changes in gradation are outside
the gradation band allowed by the stockpile tolerance in Table 4.
F.Provide a daily report and log sheet for information that that contains:
1.Calculations of the residual asphalt content of the mixture from the
equipment computer display at least three times daily.
2.The aggregate application rate from the equipment computer
display at least three times daily.
3.Aggregate used, ton (dry).
4.Daily tickets from the screening unit.
5.Micro surfacing emulsion used, ton.
6.Bituminous materials for tack coat used, if specified, ton.
7.Mineral filler used, lbs.
8.Water used in mixture, gallons.
9.Additive used in mixture, gallons.
10.Surface area completed, square yards.
11.Surface area application rate (dry lbs aggregate per square yard).
12.Percentage of asphalt residue based on dry aggregate.
1.6ACCEPTANCE
A.The Department performs acceptance sampling and testing of material
according to UDOT Minimum Sampling and Testing Requirements.
B.The Department will assess price adjustments based on the average daily
application rate of aggregate and residual asphalt per lot, using the Contractor’s daily report, as verified by the Engineer. See this Section, Article 1.5 F.
1.Calculate the pay factor and apply it to the square yard micro
surfacing item.
a.Pay Factor = PFrate (Table 1) x PFresidue (Table 2),.
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C.The aggregate application rate pay factor (PFrate) is based on the
application rate of dry aggregate.
1.The aggregate application target rate is 25 lbs/yd2
Table 1 Aggregate Application Rate Pay Factor Average Application Rate (lbs/yd2) PFrate 25.0 or Greater 1.0 20.0 to 24.9 (Avg. Rate ÷ 25) Less than 20.0 Reapplication with option to remove
D.The residual asphalt pay factor (PFresidue) is based on the emulsified
asphalt residue and content placed for each lot.
1.The Target Value is the Residual asphalt target value for emulsion,
based on the mix design.
2.The emulsified asphalt residue is provided on the Certificate of
Compliance from the Emulsion Supplier.
Table 2 Residual Asphalt Pay Factor Residual Asphalt, Daily Average (%) PFresidue (Target Value - 0.50) ≤ Daily Average ≤ (Target Value + 0.50) 1.0
(Target Value - 1.00) ≤ Daily Average < (Target Value - 0.50) 0.8 or (Target Value + 0.50) < Daily Average ≤ (Target Value + 1.00)
Daily Average < (Target Value – 1.00) Reapplication or with option to Daily Average > (Target Value + 1.00) remove and replace
E.Smoothness
1.Refer to Section 02701 for smoothness requirements.
PART 2 PRODUCTS
2.1EMULSIFIED ASPHALT
A.Use a polymer-modified asphalt emulsion manufactured specifically for
micro surfacing.
1.Refer to Table 3.
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2.The supplier must be on the approved list adhering to the UDOT
Quality Management Plan 508 Asphalt Emulsion.
Table 3 Polymer-Modified Asphalt Emulsion Test Description Micro CQS-1P(NLR) Micro CQS-1hP(NLR) Method Or Or Micro CQS-1P(SLR) Micro CQS-1hP(SLR) (a) AASHTO T59 Viscosity, 25o C, 20 Min; 100 Max 20 Min; 100 Max SFS AASHTO T59 Particle Charge Positive Positive Test AASHTO T59 Sieve Test, % 0.1 Max 0.1 Max AASHTO T59 Residue by 65 Min 65 Min -modified (b) distillation, % Emulsion Residue Testing AASHTO T49 Penetration, 25°C, 70 – 120 40 – 70 dmm AASHTO T53 Softening point, °C 55 Min 57 Min AASHTO Elastic Recovery, 60 Min 60 Min T301 5 cm per min.,
(Modified)(c), 25°C, %
(d)
(a)Generally used for Washington County
(b)Modified distillation procedure – Heat emulsion residue to 177 ± 5° C and maintain that
temperature for 20 min. Perform the distillation within 60 ± 15 min.
(c)Modify paragraph 4.5 as follows: Stop the ductilometer after 20 cm has been reached
and within 2 seconds, sever the specimen at its center with a pair of scissors.
(d)The polymer-modified asphalt emulsion residue is obtained from the distillation
process.
B.Mill or blend the polymer material into the asphalt or emulsifier solution
before the emulsification process.
1.Obtain certification from the asphalt emulsion manufacturer that the
emulsion contains at least 3.0 percent polymer solids of natural latex rubber (NLR) or synthetic latex rubber (SLR) based on the weight of asphalt (asphalt residual).
2.Latex rubber must be 100 percent natural latex rubber (NLR) or
synthetic latex rubber (SLR) as specified in Section 02742S.
C.The Department reserves the right to test the emulsion and also look at
bills of lading to verify the polymer or modifier types used.
D.Formulate the polymer-modified asphalt emulsion so the paving mixture
will sufficiently cure to allow a return to traffic in one hour under application conditions.
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2.2MINERAL AGGREGATE
A.Use 100 percent crushed mineral aggregates, clean and free from organic
matter or other detrimental substances that meet the following requirements:
1.Maximum clay lumps and friable particles of 2 percent for coarse
and fine aggregates. Refer to AASHTO T 112.
2.Maximum weighted sodium sulfate soundness loss of 15 percent.
Refer to AASHTO T 104.
3.Maximum loss by abrasion of 30 percent. Refer to AASHTO T 96.
4.Sand equivalent of 65 or greater. Refer to AASHTO T 176,
alternate method 2, pre-wet method (test the sample in the wet condition).
5.Minimum polishing value of 31. Refer to AASHTO T 278 and T
279.
a.Do not use predominantly limestone or dolomite aggregates.
B.Establish a job mix or target gradation within the gradation band as
specified in Table 4.
1.Base the mix design on the target gradation.
2.Verify that the percent passing each sieve does not vary by more
than the stockpile tolerance from the target. Refer to AASHTO T 11 and AASHTO T 27.
Table 4 Gradation Limits Job Mix Gradation Target Band Stockpile Sieve Size Percent Passing Tolerances ⅜ 100 0 #4 75-85 ±5 #8 50-65 ±5 #16 33-45 ±5 #30 24-29 ±5 #50 16-21 ±4 #100 10-15 ±3 #200 7-13 ±2 The percent passing is based on total aggregate (dry weight) and fine and coarse aggregate with approximately the same bulk specific gravities.
Micro Surfacing
2.3MINERAL FILLER
A.Use one of the following for Mineral Filler. Refer to AASHTO M 17.
1.Non-air entrained Type I/II Portland cement. Refer to AASHTO M
85.
2.Hydrated lime, free from lumps or foreign matter. Refer to Section
02746.
B.Determine the amount of mineral filler needed through the laboratory mix
design.
1.The amount of mineral filler used must be between 0.5 percent and
2.0 percent by the weight of dry aggregate.
2.Adjust the percentage of mineral filler ± 0.5 percent as necessary
for better consistency or to optimize set times with Engineer’s approval.
3.Mineral filler is considered separately from the aggregate gradation.
2.4WATER
A.Use potable water free from harmful salts, reactive chemicals, and any
other contaminants.
2.5ADDITIVES
A.Use additives as required to accelerate or retard the break-set of the micro
surfacing mix, to improve the resulting finished surface, or to increase adhesion.
1.Determine the initial additive quantities from the mix design for the
micro surfacing mix or individual materials.
2.Use additives compatible with the other components of the mix.
2.6JOB-MIX DESIGN
A.Design according to the specifications listed in Table 5.
1.Show each ingredient amount meets the following requirements:
a.The minimum residual asphalt content is at least 7.5 percent
by dry total weight of aggregate. The design residual asphalt content and allowable tolerances must fall at or above the 7.5 percent minimum. Determine the optimum residual asphalt content according to the requirements in Table 5.
b.The aggregate gradation target is within the job-mix
gradation design limits in Table 4.
c.Mineral filler, percentage by total dry weight of aggregate.
d.The asphalt emulsion contains at least 3.0 percent polymer
solids, based on the residual asphalt content certified by emulsion supplier. Micro Surfacing
2.Identify the optimum residual asphalt as a percentage of the dry
weight of aggregate to meet Table 5 requirements. The job mix formula tolerance is +/- 0.5% residual asphalt.
3.Identify any additives included to control mix times and cohesion.
a.Provide acceptable limits for additives.
4.Use the same materials and aggregate gradation to be used on the
project.
5.Provide a micro surfacing mixture that can be spread in variable
thickness cross-sections, ruts, scratch courses, and surfaces.
6.Changes in aggregate source, emulsion, or mineral filler will require
a new mix design submitted for approval by the engineer and a new test strip as outlined in Section 3.5.
Table 5 Mix Design Requirements ISSA Test No. Description Specification Wet Cohesion @ 30 Minutes Minimum (Set) 12 kg-cm Minimum ISSA TB-139 @ 60 Minutes Minimum (Traffic) 20 kg-cm Minimum or Near Spin Excess Asphalt by LWT Sand 50 g/ft2 Maximum ISSA TB-109 Adhesion (538 g/m2 Maximum) ISSA TB-114 Wet Stripping Pass (90% Minimum) Wet-Track Abrasion Loss One-hour Soak 50 g/ft2 (538 g/m2) *ISSA TB-100 Six-day Soak Maximum 75 g/ft2 (807 g/m2) Maximum ISSA TB-147 Lateral Displacement 5% Maximum Classification Compatibility 11 Grade Points Minimum ISSA TB-144 (AAA, BAA) Mix Time @ 77° F (25° C) Controllable to 120 ISSA TB-113 Seconds Minimum * Perform the wet track abrasion test under laboratory conditions as a component of the mix design process.
2.7EQUIPMENT
A.Use mixing equipment specifically designed and manufactured to mix and
place micro surfacing.
1.Mix the material by an automatically-sequenced, self-propelled
micro surfacing mixing machine with a continuous-flow revolving multi-blade double -shafted mixing unit that:
a.Accurately delivers and proportions the aggregate,
emulsified asphalt, mineral filler, control additives, and water. Micro Surfacing
b.Discharges the mixed product on a continuous flow basis.
2.Use a machine with sufficient storage capacity for aggregate,
emulsified asphalt, mineral filler, control additive, and water to maintain an adequate supply to the proportioning controls.
3.Use a machine capable of self-loading materials while continuing to
place micro surfacing.
4.Verify that the operator has full control of the forward and reverse
speed during applications of the micro-surfacing material.
a.Use original manufacturer designed equipment for the self-
loading device, opposite side driver stations, and forward and reverse speed controls.
B.Use a machine with a hydraulically adjustable (while applying mixture)
spreader box with a screed adjustment for yield control and an adjustment for the joint matcher.
C.Equip the micro surfacing spreader box with the following:
1.Ribbon flights mounted on an adjustable shaft to continually agitate
and distribute the materials throughout the box.
2.Curb bumpers and replaceable runners with at least 5 ft long end
runners.
3.A sufficient walkway to provide access to either side of the
spreader box so the operator can avoid walking through the freshly placed material.
4.Verify that the equipment provides sufficient turbulence to prevent
the mix from setting in the box or causing excessive side buildup or lumps.
5.Flexible seals in contact with the road, front and rear, to prevent the
loss of the mixture from the box.
6.A secondary strike-off located approximately 2 to 3 ft behind the
primary strike-off to minimize transverse corrugations and to improve surface texture.
a.Verify that the secondary strike-off has elevation and width
adjustments similar to the primary strike-off and a pivot point that can be tilted for texturing or raised completely off the surface.
b.Verify that the secondary strike-off has the same
adjustments as the spreader box.
7.The ability to side-shift the box to compensate for variations in the
pavement geometry.
8.The Capability of applying micro surfacing mixture in variable
widths up to 15 ft.
D.Use a rut-filling spreader box specifically designed to fill ruts with an
average depth greater than ½ inch. Ruts greater than ½-inch deep require multiple passes to restore the cross section. Micro Surfacing
E.Use a computerized material monitoring system with integrated material
control devices such that the amount of each material can be determined at any time.
1.Calibrate each material control device before each mix application
and as often thereafter as deemed necessary by the Engineer.
2.Use a monitoring system capable of recording, displaying, and
printing the following information:
a.Individual sensor counts for emulsion, aggregate, mineral
filler, water, and additive.
b.Aggregate, emulsion, and mineral filler output in pounds per
minute.
c.Percentages of emulsion, mineral filler, water, and additive.
d.Cumulative totals of aggregate, emulsion, mineral filler,
water, and additive.
e.Scale factor for all materials.
F.Verify the daily totals from the computerized monitoring system for the
aggregate and the daily total from the scalping-screen weighing system are within 2 percent.
G.Calibrate each mixing unit in the presence of the Engineer before
construction.
1.Do not use any machine until calibration has been completed.
2.During the project construction, any mechanical change to the
equipment components that deliver micro surfacing materials to the pug mill mixer will require new calibration.
PART 3 EXECUTION
3.1LIMITATIONS
A.Do not apply micro surfacing during rain or other adverse weather
conditions within 48 hours after a rain event. Allow pavements and cracks to dry thoroughly after significant rain events before applying micro surfacing, to avoid trapping moisture in the underlying pavement layer.
B.Do not apply micro surfacing if either the pavement or air temperature is
below 50 degrees F.
C.Do not apply micro surfacing when the temperature is projected below 37
degrees F within 48 hours of placing micro surfacing.
D.Cease micro surfacing operations when the weather or other conditions
prolong opening road surface to traffic beyond two hours. Micro Surfacing
E.Remove and replace the micro surfacing if any of the following occurs:
1.Lumping, balling, or unmixed aggregates.
2.Separation of the coarse aggregate from the emulsion and fines.
3.Excessive breaking of emulsion inside the spreader box.
4.Streaking caused by oversized aggregate.
5.Flushing or excessively rich areas appearing in the micro surfacing
after two hours from the time of placement.
6.Any measurable rutting, shoving, or other evidence of premature
deformation when exposed to traffic.
F.Keep traffic off the roadway surface until the micro surfacing has cured.
1.Allow for additional curing time at locations such as driveways,
intersections, and where sharp turning movements may take place or where vehicles may accelerate quickly.
3.2STOCKPILE
A.Construct individual 500-ton stockpiles of micro surfacing aggregates.
1.Engineer will test stockpiles at least one, and at most seven days,
before use.
2.Combining, altering, or moving 500-ton stockpiles may require
retesting by the Engineer before use.
B.Notify the Engineer at least seven calendar days before micro surfacing
placement in order for the initial stockpiles to be sampled and tested for acceptance.
C.Obtain the Engineer’s written acceptance of a stockpile before its use for
micro surfacing.
D.Provide stockpile Quality Control information to the Engineer for every 500
tons of aggregates to include the following:
1.Aggregate gradation meeting job-mix formula tolerances according
to Table 4.
2.Sand Equivalency. Refer to AASHTO T 176.
E.Be capable of determining aggregate moisture within 10 minutes at all
times.
F.Rework or remove material not meeting specifications from the stockpile
area. Identify stockpiles that will be reworked.
G.The Department will retest corrected material for acceptance.
Micro Surfacing
3.3PREPARATION
A.Clean the pavement surface of all dirt, sand, dust, oil, and other
objectionable material immediately before applying micro surfacing.
B.Allow unsealed cracks to dry thoroughly before applying micro surfacing
when using water to clean the road surface.
C.Cover manholes, valve boxes, drop inlets, and other service utility
entrances before surfacing.
D.Protect all structures, including items such as guardrail, guideposts,
concrete barriers, drains, and parapet walls.
3.4APPLICATION
A.Pre-wet the pavement surface as required due to local conditions by
fogging ahead of the micro surfacing box.
1.Do not create standing water on the pavement in front of the micro
surfacing box.
B.Place micro surfacing mix that meets the job-mix design.
1.Control the ingredient proportions with metering or measuring
devices on the micro surfacing equipment.
a.Use readings from the metering or measuring devices to
determine compliance with limits stated in the approved job- mix design.
2.Limit any increase or decrease in the amount of mineral filler added
to the mix during production as per Section 2.3. Mineral Filler, B.1 and B.2.
3.Limit the set-control agent to ± 1 percent of the job-mix design
quantity.
4.Verify that the emulsion submitted with the job-mix design is the
same emulsion used throughout the project.
5.Verify that the emulsion residue is ± 0.5 percent of the job-mix
design.
a.Engineer may require a new job-mix design for review if
large disparities occur.
b.Calculate the percent emulsion on the daily electronic
printout from the calibrated paver for emulsion and aggregate quantities.
Micro Surfacing
C.Produce a mixture according to the mix design and the quality control
tolerances.
1.Maintain quality control documentation and make it available to the
Engineer upon request or at completion of daily work. Refer to this Section, Article 1.5 F.
D.Pass the mineral aggregate over a vibratory scalping screen before
transfer to the micro surfacing mixing machine to remove oversize material.
1.Verify that the screening unit is capable of providing weigh tickets
for each load of material.
E.Carry a sufficient amount of micro surfacing in all parts of the spreader
box so that full width and complete coverage is obtained with no streaks or narrow spots.
1.Avoid overloading the spreader box.
2.Do not spray water directly into the spreader box during the
application of micro surfacing under any circumstances.
F.Apply micro surfacing of proper consistency at a minimum rate of 25
lbs/yd2 based on the dry weight of aggregate for each lot.
G.Apply micro surfacing for rut filling.
1.Apply micro surfacing as a scratch-coat pass using a steel or high
density rubber strike-off when required to fill ruts less than ½ inch deep or as directed by the Engineer.
2.Make multiple passes with the rut filling spreader box for ruts
greater than ½ inch deep or as directed by the Engineer.
3.Allow 24-hour cure time after filling ruts, before placing an
additional micro surfacing layer.
H.Do not apply water to freshly placed micro surfacing.
3.5TEST STRIP
A.Construct a test strip at least 500 ft long on the roadway before initial
placement.
1.Arrange for the test strip to be constructed on the project site under
anticipated placement conditions (intersections, travel lanes, approaches, time of day, temperature, and humidity) in coordination with the Engineer.
2.Construct the test strip with the job mix proportions, materials, and
equipment to be used on the project.
Micro Surfacing
3.Adjustments to the mixture formula will be permitted provided they
do not exceed the values stated in the mix design.
a.Prepare a new mix design and construct another test strip if
modifications to the mixture formula are in excess of the values in the mix design.
4.The Engineer will evaluate the test strip to determine if the mixture
set and cure properties as well as the equipment and placement techniques are acceptable.
a.Verify that the initial set is achieved within 30 minutes and
the surface shows no signs of distress when exposed to traffic after curing for 1 hour.
5.Remove and replace or repair the test strip placement, with the
Engineer’s approval and at no cost to the Department, if the test strip does not meet the conditions stated above.
B.Make necessary adjustments if test strip does not perform as required.
1.Repeat the test strip process.
2.The Engineer may require a new job-mix design if failures indicate
an ingredient problem.
3.6FINISHING DETAILS
A.Verify that the depth of each micro surfacing course does not exceed
twice the maximum aggregate size.
1.Not required when using a rut filling spreader box.
B.Verify that the finished longitudinal and transverse joints are neat and
uniform.
1.Construct longitudinal joints within 6 inches of the lane lines where
possible.
2.Verify that the overlap of micro surfacing at any joint does not
exceed 6 inches.
3.Repair the joints if any of the following conditions exist:
a.Build-up of material at the joints.
b.Uncovered areas at the joints.
c.Longitudinal and transverse joints with more than ¼ inch
vertical space between the surface and a 4 ft straightedge placed perpendicular to the joint.
4.Verify that the edges of the micro surfacing follow the centerline,
lane lines, shoulder lines, and curb lines.
5.Repair the edges if they vary more than 6 inches.
Micro Surfacing
6.Use methods approved by the Engineer to correct deficiencies.
a.Verify that the repaired surfaces are dense with a uniform
texture.
b.Repair sections with surface irregularities the same width as
the existing pass of micro-surfacing.
c.Small areas of patching are not permitted.
C.Verify that the finished micro surfacing has a uniform texture free of
scratches, tears, and other surface irregularities.
1.Repair the surface, at Contractor’s expense, if any of the following
conditions exist:
a.More than one surface irregularity ¼ inch or wider and 10 ft
or longer in any 100 ft section.
b.More than three surface irregularities ½ inch or wider and
more than 6 inches long in any 100 ft section.
c.Any surface irregularity 1 inch or wider and more than 4
inches long.
d.Any tire track damage to the fresh micro surfacing.
e.Slick spots or any area of bleeding (surface flushing).
D.Place the micro surfacing adjacent to concrete pavements or concrete
curb and gutter with a straight longitudinal edge.
1.Do not allow over-lap in these areas.
E.Maintain neat construction lines at all locations.
F.Place the micro surfacing at side streets and intersections out to right-of-
way line including around radii where applicable.
G.Use hand squeegees to spread the micro surfacing in areas where micro
surfacing machine cannot operate.
1.Lightly dampen areas before mix placement.
2.Provide complete and uniform coverage.
3.Avoid unsightly appearance from handwork.
4.Use the same type of finish in hand worked areas as applied by the
spreader box.
H.Use construction paper or comparable products so that beginning and
ending joint lines from each construction pass are straight and neat.
I.Use construction paper or comparable products to protect all roadway
utilities.
END OF SECTION
Micro Surfacing
Micro Surfacing in other states
Utah revises spec sections through supplementals and new editions. We check this one every week and email you the day it changes. Free, no account.
Source: Utah Standard Specifications for Road and Bridge Construction, 2026 Edition. Pages 439–453 of 1,331.
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