glazed paper. If the material is an RC, most of the volatiles will evaporate within 10 minutes, and the surface of the smear will become extremely tacky. This is not so for the lighter MC or SC grades, which remain fluid and oily for some time-for hours or days, in some cases.  An  800-  or  3000-grade  MC  or  SC  cutback however, also may become sticky in a few minutes. That is  because  these  grades  of  cutback  contain  such  small amounts  of  cutterstock,  therefore,  you  should  confirm the  identification  of  the  sample  by  a  prolonged  smear test. A prolonged smear test is used to identify the 800 and 3000 grades of MC or SC cutback.  In this test, a thin smear  of  asphalt  cutback  is  placed  on  a  nonabsorbent surface and allowed to cure for at least 2 hours. If at the end of that time, the smear is uncured and still quite tacky, the material is an MC or SC; however, if the smear is hard and only slightly tacky, then the material is not an MC or SC. An RC 3000 cutback will cure completely in 3 hours and an RC 800 in about 6 hours; but, an MC or SC will still be sticky even after 24 hours. The odor given off from a heated cutback helps differentiate an MC (cutback with kerosene) from an SC (cutback with fuel oil). In the heat-odor test, you heat the unknown sample in a closed container to capture the escaping  vapors.   (Use  MINIMAL  heat.)   An  MC sample will give off a strong kerosene odor. An SC sample will not smell of kerosene, but may have a slight odor  of  hot  motor  oil. Tests for Asphalt Emulsions You  can  distinguish  asphalt  emulsions  from  other bitumens in various ways as follows: 1.   By   observing   the   color   of   the   material. Emulsions are dark brown in color, but other bitumens are black. 2.  Emulsions  mixed  in  kerosene  or  some  other petroleum distillate can be detected by the appearance of  small  black  globules,  or  beads,  which  fall  to  the bottom  of  the  container. 3.  When  an  emulsion  is  mixed  with  water,  the emulsion will accept the extra water and still remain a uniform liquid. Other bitumens will not mix with water. 4. Since an emulsion contains water, a small piece of cloth saturated with it will not burn. Other bitumens will burn or flame. Once  you  have  established  that  a  bitumen  in question is an emulsion, you can then determine whether it  is  a  mixing  grade  (medium  or  slow  setting)  or  a nonmixing  grade  (rapid  setting).  To  do  so,  attempt  to mix a small amount (6 to 8 percent by weight) of the emulsion  with  damp  sand,  using  a  metal  spoon.  A fast-setting (RS) emulsion will not mix with the sand, but   a   medium-setting   (MS)   or   slow-setting   (SS) emulsion will readily mix and completely coat the sand. Identifying the emulsion as a mixing or nonmixing type is sufficient for field conditions. Difference in viscosity is  unimportant  since  there  are  so  few  grades.  No distinction is necessary between MS and SS emulsions because both are mixing types and are used largely for the same purpose. Tests for Tars A pour test is used to identify the viscosity grades of tar. Viscosity grades of road tars are comparable to the viscosity grades of asphalt cutbacks and asphalt cement, as shown in figure 13-28.  RT-1, the most fluid, is similar in viscosity to the MC-30 asphalt cutback. RT-8 is similar to grade 800 asphalt cutback. RT-12 has the approximate consistency of asphalt cement; that is, 200  to  300  penetration. Referring again to figure 13-28, you see that road tars  RT-4  to  RT-7  and  road-tar  cutbacks  RTCB-5  and RTCB-6  have  similar  viscosities;  therefore,  if  an identified tar has a viscosity range of RT-4 to RT-7, you must perform a smear test to distinguish whether it is a road tar or a road-tar cutback.   The test is performed in the  manner  previously  described  for  cutback  asphalt. Like  rapid-curing  cutback  asphalts,  road-tar  cutbacks are  thinned  with  highly  volatile  materials,  which evaporate quickly, leaving a sticky substance within a 10-minute  period.  On  the  other  hand,  because  the  fluid coal oil in road tars evaporates slowly, road tars will remain at about the same consistency at the end of an identical period. It is not important to determine whether the  road-tar  cutback  is  RTCB-5  or  RTCB-6  since  both are  used  under  approximately  the  same  conditions. LABORATORY TESTS OF BITUMENS Laboratory   testing   provides   a   more   positive identification of bituminous materials than is possible with field testing. That, however, is not the only purpose of the various laboratory tests. For example, specific gravity  testing  (discussed  in  NAVFAC  MO-330)  is sometimes needed for the purpose of other tests and for checking   the   uniformity   of   successive   asphalt shipments. Other tests are performed for mix design purposes,  for  checking  compliance  with  project 13-42