(d) Always be careful not to overheat the screed when material requires a heated screed. Overheating
may warp the screed.
(4) Cracks in the Mat -When cracks show up across the mat in various places, this is caused by the
material being unworkable and dry. It is not being compacted properly under the screed. This can be corrected
by one of the following:
(a) Increase the intensity of the vibrators.
(b) Add heat to the screed or change the specifications.
(c) Screed tear marks should not be confused with roller cracks, although they are similar in
appearance. Roller cracks are the result of too much rolling.
APPLICATION OF ASPHALTIC MATERIALS
a. Equipment and Temperature Control -Whether or not a job is successful, depends in large measure
upon the way the asphaltic materials are incorporated into the road surface. Good work requires good
equipment and skillful operation.
b. Experience has demonstrated that the best results in asphalt construction are obtained when the
work is done in summer temperatures.
c. Practically all asphaltic materials are applied at higher than atmospheric temperatures, which
necessitates heating in most cases.
d. Temperature of Use - Following is a table of temperature limits which should govern the use of
various asphaltic materials. These temperatures will insure a sufficiently liquid condition for the use which each
material is to serve.
Temperature
F
ASPHALTIC MATERIAL
Asphaltic Cements . ........................................................................................................
275-350
SC-O ...............................................................................................................................
50-120
SC-1 ................................................................................................................................
80-125
SC-2 ................................................................................................................................
150-200
SC-3 ................................................................................................................................
175-250
SC-4.................................................................................................................................
175-250
SC-5.................................................................................................................................
200-275
MC-0. ...............................................................................................................................
50-120
MC-1 ................................................................................................................................
80-125
MC- ..................................................................................................................................
150-200
MC-3. ...............................................................................................................................
175-250
MC-4 ................................................................................................................................
175-250
MC-5 ................................................................................................................................
200-275
RC-0 ...............................................................................................................................
50-100
RC-1 ...............................................................................................................................
80-125
RC-2 ..............................................................................................................................
100-175
RC-3 ...............................................................................................................................
150-200
RC-4 ...............................................................................................................................
175-250
RC-5 ..............................................................................................................................
200-275
Emulsified Asphalt ..........................................................................................................
50-120
e. General Conditions Prior to Placement of Plant Mix - Plant mixtures should only be laid upon a base
which is dry, or at least free from standing water and only when weather conditions are suitable. Prior to the
delivery of mixture on the work, the prepared base should be cleaned of all loose or foreign material.
f. Spreading Asphalt Mixtures - All hot-laid mixtures should be delivered on the work at temperatures
which will permit ready, spreading without segregation of aggregate or asphalt. For several types they are:
(1) Asphaltic surface
course .........................................................................................
225 to 325F
(2) Asphaltic concrete base
course .........................................................................................
285 to 325F
(3) Stone-filled sheet asphalt
surface course ...........................................................................
250 to 350F
(4) Sheet asphalt binder
course .........................................................................................
225 to 350F
(5) Cold-laid asphalt surface
course ............................................................. 50 to -50F
NOTE: The desired temperature should be set by the engineer for the particular mix employed. A variation of
20F from this temperature, but within limits, may be permitted.
Temperature of Mix
(1) Mix temperature requirements will vary with the type of work being done, time of day, air temperature, type of
asphalt being used, and distance material is hauled. By temperature testing and observation an operator can learn to tell
whether the mix temperature should be increased or decreased to fit his particular job conditions.
(2) Usually the asphalt plant can produce the asphaltic mixture at temperatures below that which is determined by
the paver operator to be best. Keep the temperature of the mix at the correct point to assure good mixing and coating of
the aggregate particles in the plant as well as proper workability in placing on the road.
(3) From experience with the "CEDARAPIDS" Paver, the temperature that is usually recommended is a minimum
of 250 for the medium and high penetration asphalts and a minimum of 300 for low penetration asphalts, such as 40 or
50 penetration.
NOTE: Many mat defects can be traced to incorrect temperature of mix at the Paver.
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