Specifications include, but are not limited to: I. Asphalt Surface Treatment Design General Asphalt surface treatments shall be designed so the proposed materials are of sufficient quality and have the desired properties to provide the expected performance. Proper design also ensures the proper application rates are being used. The design procedure presented herein is a modified version of the McLeod design procedure (McLeod 1969, Janisch and Gaillard 1998). The procedure is based on two basic principles: • The aggregate application rate is designed to provide an asphalt surface treatment that is one stone thick (i.e., there should be a single layer of uniformly sized chips) with minimal excess. • The voids in the aggregate are designed to be 70% filled with asphalt cement for good performance (i.e., the chips should be 70% embedded). II. Emulsion Properties Residual Asphalt Content: A portion of an asphalt emulsion consists of water, which evaporates as the binder breaks. The amount of asphalt cement that remains after breaking is referred to as the residual asphalt content. It is important to consider the residual asphalt content because it represents the amount of material that is available for bonding to the cover aggregate. In general, the residual asphalt content is about 64 to 70% (i.e., 64 to 70% of an asphalt emulsion consists of asphalt cement). As mentioned, the objective of this design procedure is to achieve 70% embedment of the average-sized aggregate. To accomplish this, the emulsion must be at the top of the average-sized aggregate before curing. If only 70% of the cover aggregate is covered initially, the asphalt height will be about 30% too low after curing. III. Aggregate Properties Median Particle Size: The median particle size is the theoretical size through which 50% of the material passes. It is determined from the gradation chart using the following sieve sizes: 1 inch, 3/4 inch, 1/2 inch, 3/8 inch, 1/4 inch, #4, #8, #16, #50, and #200. Flakiness Index (SD 203): The Flakiness Index is a measure of the percentage, by weight, of flat particles. It is determined by testing a sample of aggregate particles for their ability to fit through a slotted plate. The weight of the material passing the slots is divided by the total weight of the aggregate sample to determine the percent of flat particles or Flakiness Index.
