• Home
  • Download PDF
  • Order CD-ROM
  • Order in Print
BITUMENS AND BITUMINOUS-MATERIALS   TESTING - 14070_301
Figure 13-28.-Viscosity grades at room temperature.

Engineering Aid 1 - Advanced Structural engineering guide book
Page Navigation
  278    279    280    281    282  283  284    285    286    287    288  
Table 13-4.-Penetration  Grades and AP Numbers of Asphalt Cement bituminous  cement  are  to  hold  the  aggregate  particles together and to seal the surface, which then resists the penetration  of  water. Bituminous cements are available in several forms suitable   for   different   procedures   of   mixing   or application  under  wide  variations  in  temperature.  Some asphalts  and  tars  are  solid  or  semisolid  at  room temperature.  Other  grades  are  relatively  viscous  (thick) liquids at room temperatures, and all become liquid at higher temperatures. Mixing bitumens with petroleum solvents or water produces  cutbacks or emulsions that become  liquid  at  atmospheric  temperatures.  Such  liquid asphalts and tars are used for cold mixes or applied as sprays  in  building  pavements. ASPHALTS.— Asphalts may be natural or manu- factured and they maybe solid, semisolid or liquid in consistency. Natural asphalts occur in lakes (as lake asphalt), pits, or rock structures (as rock asphalts). Asphalt  cement  is  one  of  the  by-products  from  the refining of crude petroleum. Generally, the military engineer depends upon the manufactured  asphalts  that  are  obtained  when  crude petroleum  is  refined  for  the  purpose  of  separating  the various  fractions  (fig.  13-26).  The  crude  oil  vapors  are separated  into  gasoline,  kerosene,  and  fuel  oils,  and  the residue  is  asphalt  cement  and  lubricating  oils.  The longer the process and the higher the temperatures, the harder the residue becomes because of the increased loss in  volatiles. Asphalt   cement   is   commercially   available   in different  standard  ranges  of  consistency  (grades).  The ranges  for  the  penetration  grade  are  based  on measurements by the penetration test in which the relative hardness of asphalt cement is determined by the distance  that  a  standard  needle,  under  a  standard loading, will penetrate a sample in a given time under known temperature conditions. The asphalt petroleum (AP) number is a number from 00 to 7 that is assigned to  these  penetration  ranges.  Table  13-4  lists  the  ranges presently  recognized  along  with  relative  consistencies corresponding to those ranges. Asphalt  cement  is  also  graded  on  the  basis  of viscosity, using special testing equipment (not in the Naval  Construction  Force  Table  of  Allowance)  to measure the time that a given amount of liquid asphalt material will flow through a tube of standard dimensions under  rigidly  controlled  temperature  and  pressure conditions.  Multiplying  that  measured  time  by  a calibration factor for the equipment gives a numerical designation called kinematic viscosity, measured in stokes (square centimeters per second) or  centistokes (stokes  100). The viscosity grades of asphalt cement are available in two series. One series includes grades AC-2.5, AC-5, AC-10, AC-20, and AC-40. The other series includes grades  AR-1000,  AR-2000,  AR4000,  AR-8000,  and AR-16000.   Normally,   but   not   always,   the   lower viscosity-graded  asphalts  correlate  with  the  softer asphalts having higher penetration values, and the higher  viscosity-graded  asphalts  correlate  with  the lower  penetration  grades. Since all asphalt cements are solid or semisolid at room temperature (77°F), they must be converted in one of three ways to a fluid state before they can be pumped or sprayed through pipes or nozzles and be mixed with aggregate. One way to liquify an asphalt cement is to heat it. Then, when it cools, it becomes a semisolid cementing  material.  The  other  methods  to  liquify asphalt  cement  are  dissolution  (producing  cutback asphalt)  and  emulsification  (producing  emulsified asphalt). CUTBACKS.– When  asphalt  cement  is  dissolved in volatile petroleum solvents (called cutterstock or flux  oils),  the  resulting  liquid  is  known  as  cutback asphalt. The idea behind cutback asphalt is that upon 13-36







Western Governors University

Privacy Statement
Press Release
Contact

© Copyright Integrated Publishing, Inc.. All Rights Reserved. Design by Strategico.