What is Liquid Asphalt (Asphalt Cement)?
First, it’s not “tar.” natural asphalt may be a natural substance that has some amazing physical properties. It’s sticky (adhesive) and it’s elastic, able to stretch, bend and flex while not breaking (cohesive). This material will a wonderful job of waterproofing. At air temperatures, asphalt cement may be a terribly, terribly thick liquid (highly viscous). once heated, it becomes thinner and easier to use. natural asphalt has been used since before Roman times as a glue and for water proofing. in an exceedingly few places within the world, it’s naturally occurring, like in a lake on the island of Trinidad and within the Labrea “tar pits” in downtown la. the majority of the asphalt used nowadays for paving comes from petroleum crude oil. Liquid natural asphalt is that the heaviest a part of the crude what’s left in any case the volatile, light-weight fractions are distilled off for products like gasoline. In Europe and Canada, it's normally known as bitumen.
Asphalt is supplied in many different grades. Typically, softer asphalts are used in colder temperatures and tougher asphalts in hotter climates. The us government sponsored a multi-million-dollar research project (Strategic route analysis Program, SHRP) within the 1990’s that developed new standards for natural asphalt binders known as performance grade (PG) binders. for instance, a PG 64-22 is meant to be used wherever average surface (high) pavement temperatures within the sun reach 64°C (147°F) and lows reach -22°C (-8°F). Premium grades sometimes have polymers or alternative modifiers to be used in heavy duty applications like intersections on city streets or airports or in extreme climates.
At normal temperatures, natural asphalt is just too stiff to combine with the aggregates. There are 3 ways to thin it enough to make it mixable heat it, dilute it with a solvent (cutback) or emulsify it in water.
By the way, “tar” (or coal tar) may be a product made from coal.