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Hot Mix Asphalt: 3 Common Varieties

Almost all of the asphalt you encounter in your daily life is a type of so-called hot mix asphalt. Yet what many people fail to realize is that there are a number of types of hot mix asphalt. Whether you work in the paving industry, or are simply interested in learning more about the asphalt options available today, read on. This article will touch on three common types of hot mix asphalt.

Asphalt Basics

All asphalt consists of two principal ingredients: binder and aggregate. The binder, a product of the petroleum refining process, functions as a sort of adhesive, holding the aggregate in place. This aggregate consists of stone--most commonly gravel--that has been crushed to a predetermined size. As you will learn below, the size of a particular asphalt's aggregate has a lot to do with its overall structural properties.

Dense Grade

Dense grade is a type of asphalt containing a variety of aggregate sizes in roughly equal proportions. These bits of stone range from a sand-like powder to coarse chunks the size of an acorn. This range of aggregates allows the asphalt to form an especially tight and dense structure, once the aggregate has interlocked during the compaction process. Dense grade asphalt is perhaps the most common asphalt in use today, thanks to its strength and low price point.

Stone Matrix

Stone matrix, often referred to as a gap-grated mix, differs from dense grade in that aggregates in the middle of the size range are left out. That means that the larger particles are able to press against one another more directly. This lends a greater degree of stiffness to the asphalt. As a result, it is less likely to continue compacting under the weight of vehicles--a problem that often causes ruts to form in other types of asphalt.

Expect to pay more for a stone matrix asphalt than for a dense grade. This price increase is tied to the fact that the hardness standards for the aggregate used are more exacting. In other words, because more pressure will be exerted on the large aggregate, it must consist of a denser and stronger type of stone.

Open Grade

Open grade asphalt is distinguished from the two varieties above in that it deliberately omits fine aggregate. By using only medium to large sized chunks of aggregate, a much more porous asphalt is created. Open grade asphalt is thus much more permeable where water is concerned. This increase in drainage is especially valuable when constructing roads in wet areas, as it reduces both the amount of tire splash, and the risk of a hydroplaning vehicle. Contact a company like Northern Asphalt LLC for more information.