The application of a seal coat has a number of functions however one of the most important is to waterproof the pavements, protecting them from water damage and oxidation. If pavements were sealed early in their life, e.g. within a year, the pavements would last a lot longer.
Under slurry seals I am including standard Slurry Seal, Microsurfacing, the Rubberized Emulsion-Aggregate Slurry (REAS), a special seal developed to stop emission of radon gas from uranium tailing piles, and the parking lot seals.
None of the above seals will prevent crack propagation when place upon cracked pavements. However there are other seals which will be discussed in a later blog that will repair cracked pavements.
Standard Slurry Seals. Slurry seals are mixes of asphalt emulsions and a well graded aggregate that are placed over a pavement to waterproof and to replace the fines that have raveled away. They come with three gradations, Type I which is the finest, Type II, which is the one mostly used and Type III, which is the coarsest. The exact gradations are usually those specified by the International Slurry Seal Association (ISSA), however often certain agencies will adjust them. The first slurry seal that I saw was mixed in a concrete mixing truck and was made with an SS-1h asphalt emulsion. Today the emulsions that we work with are quick set, which means that in a short time after mixing with the aggregate, the mix sets, kicking out the water and allowing traffic on the slurry. They are now mixed and placed by special trucks that can carry water, emulsion, aggregate and additives. The chemistry is intriguing, but too complex to discuss here.
Microsurfacing. Microsurfacing is a more robust type of slurry which uses primarily the Type III coarse gradation however Type II will also be used. It is designed to fill in areas in which there is more severe damage. The test criteria are more challenging than for a simple slurry seal.
REAS. The Rubberized Emulsion-Aggregate Slurry was developed to be able to be able to use tire buffing in a slurry seal like surface coating. The formulation is quite complex and covered by certain patents. It is specified in the Standard Specifications for Public Works Construction (Green Book) of Southern California.
Seal to Stop Emission of Radon Gas from Uranium Tailing Piles. This was developed on a special project but has not been put into practice as far as I know. It is based upon Slurry Seal quick set technology. Radon has a half life of only about 3 ½ days. If it takes more than 30 days for radon to diffuse through the coating, it is essentially blocked. We used helium gas in our research then turned the technology over to our client who confirmed our data with radon.
Parking Lot and Drive Way Seals. These seals are designed to primarily water proof, fill in minor loss of matrix fines and, actually, be black. The compositions are proprietary but essentially are emulsion based with fine fillers. A specification for this type of seal is also in the Standard Specifications for Public Works Construction (Green Book) mentioned above, however there are other specifications available from suppliers. They do an excellent job in preserving pavements.