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      Texas Natural Resource Conservation Commission  
                   Interoffice Memorandum

      Office of Air Quality, New Source Review Program
                Mechanical Section Memorandum

Date:  October 18, 1995         Policy No.: 19
From:  David Lusk
Approved by:  Gary Wallin, P.E., Section Manager
Subject:  Approving Asphalt Concrete Plant Additives Under
          S.E. 106


Standard Exemption 106 may be used to authorize use of
additives to asphalt concrete mixes provided the emissions 
meet the requirements of the exemption.  Additives are limited
to anti-strip chemicals, styrene butyl rubber (SBR-latex),
styrene butadiene styrene (SBS), other equivalents, and
recycled asphalt products (RAP) when introduced into the drum. 
Modified recycled tire rubber (crumb rubber) is specifically
excluded because the emission rates associated with this
material would limit production rates to an impractical level.


Asphalt concrete plants and the use of additives are
authorized by Standard Exemption 99.  Since no standard
exemption specifically authorizes changes to the mix formulas
for existing facilities,  S.E. 106 can be applied.  S.E. 106
was created to exempt minor modifications to existing

Crushing operations associated with the Asphalt Concrete Plant
would be subjected to permit or exemption under S.E. 73 for
rock crushers.

Manufacturers' lab analysis for anti-strip additives resulted
in a very small percentage of the anti-strip product in
emissions.  In one anti-strip manufacturer's lab analysis,
approximately 0.4% anti-strip by weight became volatile and
was emitted.  Results, in some cases, were not ever
quantifiable because of water gain in the sample.  For a
typical operation, anti-strip additives are about 1% by weight
of the liquid asphalt.  Based on the lab analysis and if 0.4%
were to be most severe contributor of emissions, then an
asphalt concrete plant with these characteristics would
conservatively be allowed a maximum production rate of 250
tons per year.  Based on the Mechanical Section engineering
experience and judgement, most asphalt concrete plants,
although producing more per hour, have fewer emissions and 
can be authorized for anti-strip additives under S.E. 106(d)
for compounds with no L value listed.  See sample calculations


           5% of total mix is liquid asphalt
           1% of liquid asphalt is anti-strip
           0.4% of anti-strip is volatilized
           (conservative fraction)

Emissions = 0.05 x 0.01 x 0.004 x 250 tons/hour x 2000 #/ton
 = 1 #/hr

Manufacturers' lab analysis for other common  additives ( SBS,
SBR, Gilsonite, EVA, etc.) resulted in no significant,
measurable emissions.  These additives are typically 6 to 10%
of the liquid asphalt which constitute about 5% of the total
mix.  Quantifying emissions from additives like these is
difficult, if not impossible, for several reasons: 

1) According to MSDS information, these compounds are stable
at storage and mixing temperatures, 
2) Manufacturers have shown that the character of emissions
from these compounds is undistinguishable from unmodified
asphalt, and 
3) Laboratory analysis has demonstrated that emissions from
these materials were below detectable levels with the
equipment and operating temperatures of ACP. 

Based on this information, S.E. 106 (d) for compounds with no
L value would be used.  Stack sampling results while using RAP
into the asphalt concrete mixes are not statistically
different than that of virgin aggregate provided the material
is introduced into the drum section and shielded from the
flame.  Since RAP displaces aggregate on a one to one basis,
no new emissions are expected from handling the RAP.  Crushing
of material is not allowed under this exemption and must be
qualified under the appropriate exemption (#73). Note:  Some
facilities disconglomerate or break up recycled asphalt
material with a reclaimer.  A "reclaimer", by definition, is
not a crusher.  If the applicant can justify the function of
such equipment and quantify emissions, this equipment can be
qualified for S.E. 106 when emissions are less than 6#/hr of
the listed pollutant, i.e. limestone.

Necessary Action(s):

Obtain documentation from the company establishing that
additives will not create emissions greater than one pound per
hour.  This can be accomplished through calculations or a
statement to this effect. 

Some anti-strip amine based additives have offensive odors and 
may contribute to nuisance conditions.  The applicant must use
a low or no odor material if nuisance conditions exist.

In the event the facility applies for a permit or is subject
to a permit renewal, the operations authorized under S.E. 106
shall be incorporated into the permit per the requirements of
116.211, (d), with no changes to the maximum allowable
emissions rates table (MAERT).

Cold mix and rubber modified (crumb rubber) mixes production
at asphalt concrete plants cannot be authorized under this
standard exemption due to higher than allowed emission rates. 
The facility would have to produce less than 1 ton of mix per 
hour to qualify.  These mix types may be authorized under S.E. 

cc:  All Mechanical Section