• Home
  • Download PDF
  • Order CD-ROM
  • Order in Print
Asphalt  Cutbacks
Use of Asphalt Emulsions

Equipment Operator Advanced - Advanced construction equipmet operators manual
Page Navigation
  167    168    169    170    171  172  173    174    175    176    177  
Table  8-4.-Asphalt  Emulsions  According  to  Their  Electric  Charge Grades of Asphalt Cutbacks When  a  great  amount  of  cutterstock  is  added  to  a given amount of asphalt cement, a very thin liquid results. Viscosity grade is a measure of the relative consistency  of  an  asphalt  bitumen  after  cutterstock  is added to a fixed amount of it. The grade is designated by a number that corresponds to the lower limit of the viscosity of asphalt cutback as determined by a standard test. The upper limit of viscosity is defined as twice the lower  limit. The viscosity grades of RC, MC, and SC are 70 (70-140),  250  (250-500),  800  (800-1,600),  and  3,000 (3,000-6,000). The numbers in parenthesis are the lower and upper limits of viscosity, In addition, MC has a grade 30(30-60). The grade ranges are 30 (most fluid) to 3,000 (least  fluid). Uses of Asphalt Cutbacks Different types and grades of asphalt cutbacks are used to meet various climate conditions for different types  of  pavement.  Asphalt  cutbacks  are  usually  used for  prime/tackcoats  and  for  bituminous  surface treatments.  The  prevailing  atmospheric  temperatures existing during construction projects are a major factor in  selecting  the  grade  of  asphalt  cutback.  The  heavier grades are preferred for use in warm weather; the lighter grades in cool weather. When the preferred grade of a given  type  of  asphalt  cutback  is  not  available,  a comparable grade of another type may be substituted; for example, RC-800 maybe used instead of MC-800, or RC-70 instead of MC-70, without seriously affecting the  finished  pavement. Light grades of asphalt cutback maybe produced in the field by adding solvents to asphalt cutback. The composition  of  asphalt  cutbacks,  expressed  in  percent of total volume, is shown in table 8-3. Asphalt  Emulsions An  asphalt  emulsion  is  a  nonflammable  liquid substance, composed of asphalt cement, water, and an emulsifier mixed together to produce a liquid material. Emulsions  are  environmentally  friendly,  have  the  same basic  uses  as  cutbacks  and  are  becoming  more commonly used in the field. Asphalt and water will not mix; therefore, a chemical agent called an “emulsifying agent”  must  be  added.  The  emulsifying  agent  keeps  the asphalt cement suspended in the water and controls certain physical properties of the emulsion. Common emulsifying agents are soaps, animal blood chemicals, and  certain  specified  colloidal  clays  in  dust.  When emulsion is applied to a surface, the water and asphalt cement break (separate), leaving a thin film of asphalt cement. The speed of separation, referred to as  setting rate, is the basis for designating an asphalt emulsion. The setting  rates  are  rapid,  medium,  and  slow.  The  letter symbols   for   these   rates   are   RS,   MS,   and   SS, respectively. Asphalt emulsions are classified into two types: those that are negatively charged and those that are positively charged (table 8-4), Emulsified asphalts may be of either the anionic electro (negatively) charged asphalt  globules  or  cationic  electro  (positive)  charged asphalt globules. The asphalt emulsions are graded on the basis of viscosity and grouped according to their use. 8-21







Western Governors University

Privacy Statement
Press Release
Contact

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