Slurry Seal

The following specification is for basic standard unmodified slurry seal for use in areas where the longer life cycles of polymer-modified and black aggregate are not required. Before using this specification the user must reduce the aggregate types listed under 2.01 (c) to only one. Type I may be used for parking lot resurfacing but should only be specified if it is readily available. Type II may also be used for parking lots, streets and arterials. Type III is used for arterials and highways.


1.01  SCOPE

Slurry Seal shall consist of mixing asphalt emulsion, aggregate, and water and spreading the mixture on a surfacing or pavement where shown on the plans, as specified in these specifications and the special provisions, and as directed by the Engineer.


The materials for slurry seal immediately prior to mixing shall conform to the following requirements:

2.01 (a)  Asphalt Emulsion

Asphalt emulsion shall be a cationic quick-setting type conforming to the requirements for CQS-1H grade under CalTrans Standard Specifications, July 1992, Section 94, Table 4, requirements for "Quick Setting Asphalt Emulsion".

2.01 (b) Water

Water shall be potable, free of harmful salts and shall be of such quality that the asphalt will not separate from the emulsion before the slurry seal is in place in the work.

2.01 (c)  Aggregate

Aggregate shall consist of sound, durable, crushed stone or crushed gravel and approved mineral filler.  The material shall be free from vegetable matter and other deleterious substances.  Aggregates shall be 100% crushed with no rounded particles.  The percentage composition by weight of the aggregate shall conform to one of the following gradings:


3/8" -- 100 100
No. 4 100 90-100 70-90
No. 8 90-100 65-90 45-70
No. 16 60-90 40-70 28-50
No. 30 40-65 25-50 19-34
No. 200 10-20 5-15 5-15
Theoretical asphalt 
content, % dry 
10-12 7.5-13.5 6.5-12
Approx. application
rate (pound per 
square yard)
8-12 10-15 15-25

The aggregate shall also conform to the following quality requirements:

Sand Equivalent 217 D2419 55 Min.


Asphalt emulsion shall be added at a rate of from 11 to 25%.  A job mix design shall be submitted by the Contractor for approval by the Engineer that conforms to the specification limits, and that is suitable for the traffic, climate conditions, curing conditions and final use.

The Slurry Seal mixture shall be proportioned by the operation of a single start/stop switch or lever which automatically sequences the introduction of aggregate, emulsified asphalt, admixtures, if used, and water to the pugmill.

Calibrated flowmeters shall be provided to measure both the addition of water and liquid admixtures to the pugmill.  If necessary for workability, a retarding agent, that will not adversely affect the seal, may be used.

Water, and retarder if used, shall be added to ensure proper workability and (a) permit uncontrolled traffic on the slurry seal no more than three (3) hours after placement without the occurrence of bleeding, raveling, separation or other distress; and (b) prevent development of bleeding, raveling, separation or other distress within seven (7) days after placing the slurry seal.

Uniformity of distribution of asphalt will be determined by extraction tests in accordance with California Test 310.  The average bitumen ratio (pounds of asphalt per 100 pounds of dry aggregates) shall not vary more than five (5) percent above or below the amount designated by the Engineer.  This requirement shall apply to samples taken from any location or operation designated by the Engineer.

2.03  MIXING

The Slurry Seal shall be mixed in a self-propelled mixing machine equipped with a continuous flow pugmill capable of accurately delivering and automatically proportioning the aggregate, emulsified asphalt, water and admixtures to a double shafted, multiblade pugmill mixer capable of minimum speeds of 200 revolutions per minute.

A minimum of two mixing machines shall be maintained on each project of a 12 cubic yard or larger capacity.  The slurry seal retention time in the pugmill shall be less than three seconds.  The mixing machine shall have sufficient storage capacity of aggregate, emulsified asphalt, and water to maintain an adequate supply to the proportioning controls.

The mixing machine shall be equipped with hydraulic controls for proportioning the material by volume to the mix.  Each material control device shall be calibrated, properly marked, preset and lockable at the direction of the Engineer.  The mixing machine shall be equipped with a water pressure system and nozzle type spray bars to provide a water spray immediately ahead of the spreader box.

The mixing machine shall be equipped with an approved fines feeder that provides a uniform, positive, accurately metered, pre-determined amount of a mineral filler, if used, at the same time and location that the aggregate is fed.


The slurry mixture shall be uniformly spread by means of a controlled spreader box conforming to the following requirements:

The spreader shall be capable of spreading a traffic lane width and shall have strips of flexible rubber belting or similar material on each side of the spreader box and in contact with the pavement to prevent loss of slurry from the box and the box shall have baffles, or other suitable means, to insure uniform application on super-elevated sections and shoulder slopes.

The rear flexible strike-off blade shall make close contact with the pavement and shall be capable of being adjusted to the various crown shapes so as to apply a uniform seal coat.

Slurry mixture, to be spread in areas inaccessible to the controlled spreader box, may be spread by other approved methods.


The slurry seal shall not be placed if either the pavement or the air temperature is below 13 degrees C (55F) and falling, but may be applied when both the air and pavement temperature is 7 degrees C (45F) or above and rising.  The mixture shall not be applied if high relative humidity prolongs the curing beyond a reasonable time.

Before placing the slurry seal, the pavement surface shall be cleaned by sweeping, flushing or other means necessary to remove all loose particles of paving, all dirt and all other extraneous material.

Prior to 24 hours before beginning slurry seal operations, the contractor shall notify all residents, businesses and agencies by an approved written notice detailing streets and limits of work to be done and the hours of work.  The contractor shall also 24 hour post all streets that are to be worked upon with temporary "No Parking - Tow Away" signs at 100 foot intervals.  These signs shall also state the day of the week and hours of no parking.

Immediately before commencing the slurry seal operations, all surface metal utility covers (including survey monuments) shall be protected by thoroughly covering the surface with an appropriate adhesive and oiled or plastic paper.  No adhesive material shall be permitted to cover, seal or fill the joint between the frame and cover of the structure.  Covers are to be uncovered and cleaned of slurry material by the end of the same work day.

Hand tools shall be available in order to remove spillage.  Ridges or bumps in the finished surface will not be permitted.  The mixture shall be uniform and homogeneous after spreading on the surface and shall not show separation of the emulsion and aggregate after setting.

Adequate means shall be provided to protect the slurry seal from damage from traffic until such time that the mixture has cured sufficiently so that the slurry seal will not adhere to and be picked up by the tires of the vehicles.


Slurry seal will be measured and paid for by the square yard for the actual surface area covered.


The contract price paid per square yard for slurry seal shall include full compensation for furnishing all labor, materials, tools, equipment and incidentals and for doing all the work involved in the furnishing and placing the slurry seal complete in place, including cleaning the surface and protecting the slurry seal until it has set, all as shown on the plans, as specified in these specifications and as directed by the Engineer.