15 May 2001
are determined by the Wet Track Abrasion Test as described in ASTM D 3910. Appendix C contains a
summary Design Method and an example problem for Slurry Seals. The method is intended to furnish a
starting point for field application. Slight adjustments may be required in the proportions of the mixture
to satisfy field conditions; however, a field test section should be constructed using the laboratory-
e. Factors affecting design. Some important factors that should be considered before using a
slurry seal are as follows:
(1) The cost of placing a slurry seal is relatively small, but this mixture does not provide
additional strength to the pavement and does wear rapidly under a high volume of traffic.
(2) Slurry seal will fill and seal many surface cracks.
(3) Slurry seal can be used to seal a pavement surface to retard oxidation and raveling or to
provide a thin (6 millimeter, 1/4-inch) wearing surface.
(4) Skid resistance can be improved if the proper crushed aggregates are used in the mix.
(5) Uncured slurry seal can be adversely affected by changes in weather conditions.
(6) A treated pavement must be closed to traffic to allow the slurry seal to cure (sometimes as
long as 24 hours, but usually 6 hours).
(7) Slurry seal is better suited for a pavement subjected to low or moderate traffic because
(8) Only structurally sound pavements are suited for a slurry seal.
(9) Proper design and application are very important for obtaining a satisfactory job.
(10) Generally, slurry seals have a 2- to 5-year life.
(11) A properly placed slurry seal will fill small cracks and coat the surface of the pavement to
a depth of 3 to 6 millimeters (1/8 to 1/4 inch).
f. Surface preparation. Without proper surface preparation, the life expectancy of a slurry seal
surface is reduced. All loose material (including loose or flaky paint), dirt, and vegetation should be
removed. Cracks wider than 3 millimeters (1/8 inch) should be treated before applying the seal coat.
After the surface is cleaned, a light tack coat should be applied to improve the bond and to reduce the
asphalt absorption of the old surface.
g. Application. Surface texture of the fresh slurry seal will be affected by the condition of the
flexible lining of the spreader box, fragments of cured slurry adhering to the edges of the lining or to the
squeegee, and the condition of the burlap drag. Worn lining will result in an uneven thickness of the
seal coat. Fragments of cured slurry seal or large aggregate particles caught in the lining will produce
gouges and streaks. The burlap drag should be washed or replaced as needed to insure that
accumulations or crusts of mix do not cause scars or streaks. The mesh basket screen that is hung at
the end of the discharge chute should be emptied and cleaned as required. The slurry seal should be
checked for lumps or balling which can be caused by inadequate mixing or premature break of the
asphalt emulsion. Deviation of the mix from the specified gradation may also result in an unsatisfactory