Lesson 1/Learning Event 5
Learning Event 5
FIELD IDENTIFICATION OF UNKNOWN BITUMINOUS MATERIALS
Identifying unknown bituminous materials has been, and still is, a major problem. Stockpiled
bituminous materials that are unmarked or improperly marked can cause unnecessary delay in
construction. Some of the tests used in the field to identify bituminous materials are:
Solubility Test. The solubility test consists of taking a small amount of the unknown
bituminous material, enough to cover the head of a nail if a solid, or a few drops of a liquid
material, and attempting to dissolve the material by stirring it in a petroleum distillate, i.e.,
gasoline, kerosene, diesel fuel, etc. If the material is an asphalt it will mix uniformly with the
distillate. Tars, however, will form a stringy undissolved mass. Emulsions, in addition to other
distinguishing tests, may also be identified in the solubility test since they will form undissolved
wads or balls of the emulsion at the bottom of the container of petroleum distillate.
Pour Test. If, upon performing the solubility test, the bituminous material dissolves, an asphalt
product-asphalt cement or asphalt cutback-is present. All asphalt cements are solids at room
temperature (77F), while asphalt cutbacks, on the other hand, are fluids. With these facts in
mind, you may run a second test, a pour test, to determine whether a sample is an asphalt cement
or an asphalt cutback.
In the pour test, an attempt is made to pour the material from a small container. Asphalt
cements, being solids, will not pour, while asphalt cutbacks, being fluids at 77F, will pour.
Smear Test. The smear test is used to separate an RC from an MC or SC. It is primarily based
on the fact that RCs are cut back with a highly volatile material (naphtha or gasoline). It is
possible to tell whether a sample is an RC or not by smearing some of in a thin layer on a
nonabsorbent surface such as a piece of glazed paper. This will give the volatiles a chance to
evaporate. In fact, volatiles will leave an RC smear within a few minutes. The surface will
become extremely tacky; sufficiently so that the specimen, paper and all, will stick to your
fingers and be lifted into the air if touched. Checking the reverse side of the paper you will find
that the RC did not penetrate through the paper as will MCs or SCs. MCs and SCs on smear test
will remain fluid and oily for some time; for hours or days in some cases, depending upon the
type and grade of the material.