15 May 2001
(2) Additives. Liquid additives are added during the field mixing process to provide control of
the set properties of the micro-surface mixture. The amount of additive used generally increases with
decreasing temperatures. This is because the additive acts to cause the emulsion to break or cure
faster. These additives are normally obtained from the emulsion manufacturer.
(a) General. The aggregate used should be a high quality 100 percent crushed
aggregate. Aggregates previously used for micro-texturing include granite, flint, slag, limestone, basalt,
chert, and gravel. The aggregate shall meet one of the gradation types as given in table 4-7. The
gradations used for microsurfacing are the same as those of an asphalt slurry seal, except that Type 1
the finest gradation used for a slurry seal (table 4-4) is not used for microsurfacing.
Gradation Types for Micro-Surfacing
9.5 mm (3/8 inch)
4.75 mm (No. 4)
2.36 mm (No. 8)
1.18 mm (No. 16)
600 Fm (No. 30)
300 Fm (No. 50)
150 Fm (No. 100)
75 Fm (No. 200)
(b) Mineral filler. Mineral filler is added to the mixture to obtain the desired dispersion
(reduce segregation) and working characteristics (speed up or slow down the rate of cure of the system)
of the micro-surfaced mixture. The amount of mineral filler added shall be determined from laboratory
testing and will normally not exceed 3.0 percent of the weight of the aggregate. The mineral filler may
be non-air entrained portland cement, hydrated lime, or another approved mineral additives.
(4) Water. The water should be potable, free of soluble salts or any other harmful materials.
The amount of water used should be limited to that required to produce a mixture of desired consistency.
The amount of water required may increase slightly with increasing temperatures.
d. Design. The Corps of Engineers has not developed a method of mixture design. Instead,
procedures developed by the International Slurry Surfacing Association (ISSA) are recommended for
use and are detailed here. These procedures can be broken down into three parts. The first is the
evaluation of materials to verify they meet requirements as given previously in paragraph Material
requirements of this chapter. These materials include the aggregates and the polymer-modified asphalt
cement. The second part involves testing the effects of mixing and application characteristics, water
content, filler, and additives, and determination of optimum asphalt content through the preparation of
trial mixes. The third part involves performance related tests on the mixture to ensure good long-term