Design Me thods f o r Hot-Mixed AsphaltRubbe r Conc rete Paving Materials
Jame s G. Chehovit s
I NTRODUCTION
The
properties and u se of a s phalt-rubber materials for
various paving and
maintenance
activit i es
have
been
well
documented in the lit e r a ture. The majority o f thi s li terature
r eports on propertie s of asphalt-rubber mater ial s (1-12), a nd use
of
asphalt -rubber
in
s tr ess
absor bing membranes ( SAM) and
inter l aye r s (SAMI) (13-25). Researc h s tudies have shown
that
a s phalt -rubber
mater ial s
h ave significantly modified phy s i ca l
prope rties when compared to asphalt cement. These mod i fi cations
in c lud e
inc reased
high
t emperature
modulus , viscosity, and
toughne ss ;
increased
elast i c ity ,
r educed
temperature
suscept i bi lit y , and less age hard eni ng. In several states and
countries
abroad ,
u se
of
asphalt - rubber
in S~~ and SAMI
appl i cat i o ns has
become
r out ine
construc ti on
pra c ti ce
for
r ehabilitat ing det e riora ted pavements and extending overlay life .
In the United St8tes, a sphalt-r ubbe r mater ial s have been
used on a limi ted basis as the b inder f o r ho t-mi xed asphalt
concrete
pavements.
A
r ecent
surve y by the Asphalt-Rubbe r
Produc e rs Group (ARPG) i ndicated that at l east 35 proje cts which
used asphalt-rubber b ind e r were placed between 1975 and 1987 in 12
s t ates. Several re searc h st udie s have
been
completed
whic h
investigated u se of aspha lt-rubbe r as an asphalt concrete paving
binder (26, 27) . Addit i ona lly, there have been several
we ll
documen t ed fi e ld t est projects placed by several state s (28 , 29,
30 , 31). The li terature indi cates that several o the r c ountries
ha ve used a sphal t-rubber binders f o r ho t-mixed paving (32, 33 , 34) .
Limited information i s curr ently avai l abl e o n methods to be
u sed f or de Signing hot-mixed a spha lt concrete mixtures whe n using
asphalt - rubber
binde r s.
vallerga
(35) has suggested several
s pec ifi ca ti on
changes
whi ch
sho uld
be
made
when
using
aSPhalt -rubber. Hoy t and lytt on (27) r epor ted o n a mixture design
procedure f or a spha lt-rubber paving mixtures which wa s u sed in a
lab
res ea rch
pr ogram that studied the feasibility of us ing
asphalt-rubber binder in de nse graded airfield pa vements.
The purpose of thi s paper is to describe design procedures
which
have
been
developed
since
1984
as the result of
approx imat e ly
30
ho t-mixed
paving
pro jects
which
u sed
a sphalt -rubber bind e r. Procedures f or selecti ng the asphalt-rubber
mate ri a l propo rti ons and r esu l ting desired prope rties , mixture
aggregates, and binder cont en t s f or dense , open , and gap graded
mixture types a r e pres e nted al ong with s uggested cons truction
guidelines and spec ifi cations .
FACTORS WHICH INFtUENCE ASPHALT-RUBBER PROPERTIES
The interaction whi c h occurs between asphalt and recycled
rubber has been snown to be dependent on a variety of factors:
• Asphalt physical and c hemi cal properties
• Rubber physical and chemical properties
• Time
• Temperature
• Mixing conditions (high shear or low shear)
• Use of add.i ti ves
Ea c h of these factors needs to be considered when developing an
asphalt-rubber formulation for a specific use.
Asphalt Cement
Chemical and physical properties of the asphalt influence
several properties of the asphalt-rubber.
Stiffness
(asphalt
grade)
and
tempe rature
suscept i bility
will
influence high
t emperature and low temperature performance of the asphalt- rubber.
Chemi ca l make-up o f the asphalt will influen ce the degree of
interacti on which occurs bet~en the a sphalt and the rubber.
Asphalts which have higher degrees of aromaticity tend to dissolve
and interact with rubber to a greater degree than asphalts with
lower aromatic contents .
Rubber
Several character is tics of the rubber influence properties
of
the
asphalt-rubber blend. Physical rubber c hara cteristics
including particle size (gradation) , shape (angular or elongated) , ·
surface
texture
(as
influenced
by
grinding
method) , and
contaminant presence (fibers, et c.) influence properties of the
asphalt-rubber.
Chemical
compositional
character isti cs
also
influence blend properties. These characteristics include rubber
hydroca rbon content , specific type of rubber polymer or blends
(amount
of
SBR
and
natural),
plastic izer
content ,
and
reinforcement type and content (carbon bla ck and other materials).
Time and Temperature
Various research projects have shown that the time exposure
and temperature of the asphalt-rubber blend influence physical
properties .
Increased
time
results
in greater int e ra ction.
Increased temperature results in quicker interaction.
When physical properties of asphalt-rubber are monitored,
the material will thicken (increase in viscosity) as the rubber
particles swell in the asphalt. After a period of time, depending
on temperature and mat erials properties . the rubber will begin to
break down (devulcanize and melt), and viscos ity will reduce.
Rate of devul ca nization will also be influenced by the
mixi ng conditions. Be cause of the se influences , it is important
that asphalt-rubber blend s be checked for appropriate properties
at a variety of time periods which can occur during actual use .
Mixing Condi ti ons
The amount of s h ear . or int ens ity o f mi xi n g . will influe n ce
the prope rtie s o f
the aspha lt-rubber. Produc ti on mixing ~ys t ems
are designed t o ' i ns ur e uniform wett ing and suspension of the
rub be r particle s in the asphalt.
It is impo rtant that lab mixing pro cedur es do not s ubje c t
the a sphalt-rubber t o excessive amount s of s hear whi c h could
qui c ke n the rubber d ev ul canization process.
Additives
Ext ending oils ca n be u sed t o so ften the mat e ri a l f o r
improved low t emperatur e performance a nd f or improving the d egree
of interact i on between the aspha lt a nd rubbe r . Adhe s i on agents
commonl y
used
in asphalt paving (heat stable anti-stripping
age nt s) c an be used t o imp r ove film stripping r es istance . Diluents
whi c h are used in asphalt-rubber c hip sea l appli ca ti o n must no t b e
us ed in h ot -mixed applications .
TEST METHODS FOR ASPHALT RUBBER
The phy sica l pr ope rti es of asphalt-rubber ha ve b een shown in a
vari e ty
of
st udi es
t o be substantially different tha n f o r
unmodifi ed asphalt cement (1-12). Many o f these s tudie s h ave u sed
common a sphalt te s t procedure s as well a s non- s tandard procedu r es
t o attempt t o quantify the modified physical
properti es
of
The
non-standard
procedures in c lude Schweyer
a sphalt-rubber .
Rheomete r (2 . 3) . s liding plate v is cometer (1.3). force ductility
(2.3 . 8.10).
torque
f o rk
viscosity
(2,3.8.10),
mec hani cal
spect rogr a ph (1) , and seve ral o ther s.
Physical attributes o f a s phalt-rubbe r whi c h
h o t-mixed applications inc lude :
should
considered
e Viscosity at hi g h t e mpe rature s f or appropriate mixing
compac ti o n characteristics.
• Consistency
at
high
pavement
experienced during the summer.
s urfa ce
for
and
tempe ratur es
• Cons istency at moderate temperatur es.
• Ela st i c ity
• Low temperature charac teristi cs
Testing me tho ds
8 5 f o ll ows:
whi c h ca n be used t o eva luate the se attributes are
Vi scos ity
at
high
The
viscosity
of
asphalt-rubbe r
materia l s
tempe rature s
(250-4 000 F) can easily be monitored using r o tati on a l
type viscome ters such as a Haake hand h e ld p o rtable viscometer
(1 0 ) or a Br ookfi e ld viscometer (ASTM 03236)(36).
High Tempera ture Cons i stenc y
The cons i stency of - asphalt-rubber at high pa vement surface
t emperatu r es can be indi c ated by severa l procedures inc luding Ring
and Ball Softeni ng Point (ASTM 036) . Modi fi ed Fl ow (ASTM 03407).
or a cone penetra t ion et 122 0 F (ASTM 03407 end 05)(37).
Mode rat e Temperature Consistency
Moderat e t e mpera ture (77 0F) consis t e n cy can be eva luat ed
ea s ily by using the ASTM 03407 Cone Penet ration test at 77 0 F (37),
Ela sticit y
The e la st i c ity of asphal t rubber can simpl y be eva luated
u s ing the ASTM D~407 r es ili ence te st whi c h indicates the amount of
r ebound und e r a 75 gram l oad at 77 0 F (37).
Low Temperatur e Characteristics
Severa l
t es t me thod type s c an be u sed to
provide
an
indication
of l ow temperature prope rties. These inc lude Cone
Pe netrat i on (ASTM 03407) at 32 or 39.2 o F ; Ductility at 39.2 o F
(ASTM 0113) and Low Tempera t ure Fl exibi lit y (Modif i ed ASTM C 711 .
se c ti o n 7.2 u s ing a 900 bend in 10 seconds at l ower and lowe r
t emperatures un til fra c ture occur s) (37,38).
SE LECTION OF ASPHALT RUBBER FORMULA
The physica l properties of asphal t-rubber depend on the
ingredients and intera c ti on conditions . Th e refore. to obtain the
appropr i ate
ingredients
and
int erac ti on
desired proper ti es .
cond i t i ons must be chosen . These c hoices wh i c h must b e mad e are:
e
•
•
•
Se le c ting
Se le c ting
Se lec ting
Selecting
th e
the
the
the
asphalt cement source and type.
rubber source and t ype.
rubber con t ent.
intera c ti on condition s.
Additionally, it i s impo rtant that the asphalt-rubber material
have appropriate s t abi lity of properties . si n ce prope rti es vary
with interacti o n time and time of interaction can vary during
ac tual use . Therefore, t est ing o f an a spha lt-rubbe r blend of
ing r edient s during proje c t formulation st udi es should be performed
no t j ust at a single interaction period, but at a vari ety of
inter ac ti o n pe ri ods t o evaluate stability
and
retenti on
of
pro perties. A procedur e f or interac ting the asphalt-rubbe r f o r 24
ho ur s during formulation s tudie s i s contained in Append ix 1 .
Physical properties can be evaluated from samples poured at 3D ,
60 . 90 . and 120 minut es of int e ra ction t o identify property
retention during nor mal usage period s after comp l eti o n of field
mi xi ng. Tests at 6 hour s Can iden tify properties of the blend if
a job delay occurs and the asphalt-rubber is used the same day.
Tests at 24 hours (with e~posure from 6 to 22 hours at a lower
temperature to simulate overnight unheated storage) can indicate
stability o f properties if the asphalt-rubber i s to be used the
next day.
Suggested
physica l
property
limits
for asphalt-rubber
materials for hot-mixed asphalt-concrete applications are listed
in Table 1 for hot, moderate , and cold c limates.
Asphalt-Cement
The grade of asphalt cement used in asphalt-rubber, is a
major influen ce on blend properties over the entire temperature
range.
Asphalt cement for asphalt-rubber should meet appropriate
specifications for paving use such as ASTM 03381 or 0946. Typical
grades used range from AC-2.5 t o AC-20, o r 200-300 penetration to
60-7 0 penetration. It is important that the specific asphalt
cement be compatible , or capable of interacting with the specific
rubber being used. This is indicated by appropriate increa ses in
viSCOSity during the intera ct ion period. Since the interaction
with rubber result s is an increase in high temperature modulus,
asphalt cements used are typically somewhat softer than usual
unmodified asphalts used for similar applications.
Figure s 1,2, and 3 , show results of constant load creep
tests performed on asphalt-rubber materials which contained a
variety of asphalt-cement grades each with 17% by total weight of
a minu s 20 mesh tire rubber. Testing was performed using a
procedure reported by Cotzee and Monismith (24). Data shown in
these figures indicates that addition of rubber
produces
a
stiffening
effect
at
moderate temperatures (74 0 F) which i s
approximately equivalent t o using an asphalt which is 2 to 3
grades harder . At lOOoF, the effect is even greater. At low
temperature (39 0 F) however, the effects of stiffening are much
less. For the asphalts which were approaching the brittle point
(the AC-20 and AC-7.5) at 390F. creep with rubber was very similar
to creep of the unmodified asphalt. Thi s data therefore indicates
that asphalt-rubber materials and unmodified asphalt creep at
similar rates at low temperatures near the base asphalt brittle
paint.
However, as temperature increases , the a sphalt cement
reduces in st iffness to a greater degree than the asphalt-rubber
as indicated by reduced creep of the asphalt -rubber . The effect
becomes greater as temperatures increase. The dat a suggests that
it is pOSsible to use asphalt cements in asphalt-rubber which are
softer than the normal unmodified paving grade used for the
specific application to provide reduced stiffness (higher degrees
of creep) at low temperatures and increased stiffness (reduced
creep) at high temperatures.
produce
Base asphalt grades wh i ch ha ve been found
to
asphalt-rubber
material a meeting the hot, moderate, and cold
climate property limits of Table 1 are as follows:
Climate Type
Ho t
Moderate
Co ld
Base Asphalt for Asphalt -R ubber
AR Grade
AC Gr ade
Penetration Grade
AR-4000,AR- 2000
AR-IOOO
AR-1000 with 3%
to 6% extender
AC- 20 , AC-I O
60-70, 85-100
AC- 5 , AC- 2.S
120-150,200 -300
200- 300 with 0-3%
AC 2 . 5 with
0-3% extender extender
Var i ous extending oi l s can be
used
in
asphalt-rubber
materials t o inc r ease the intera c ti o n between the asphalt and
rubbe r, and to improve l ow t empe rature performance by decreasing
the stiffness of the asphalt - rubber when softer asphalt grades are
not a vailable. Extender types u sed are generally n apt henic or
aromat i c petrol eum oi l s whi c h have a minimum flash point of 400°F.
For most common o il s with viscosities between 500 and 3000
SUS at 1000F, approximately 3X by asphalt weight is requi r ed to
soften an asphalt an equ ivalen t of 1 grade . Typi ca ll y , each
percent of extender oil l owers ring and ball soften ing point (ASTM
0 36) r esults by 1 . 5 to 2.0 degrees Farenheit.
Rubber
Rubbe r u sed for aspha lt-rubber should be primarily made from
r ecyc l ed
pneumatic
tires .
The
rubbe r s hou ld be ground on
appropriate systems, a nd s hou ld
be
free
from
con t aminants
in c luding mineral matter , fiber and metal . The rubber should be
sufficiently dry to prevent foaming when added to hot asphal t.
Generally this means a moisture content o f les s than 0.75%.
Mine ral contaminants shou ld no t exceed 0.25%. The rubber may be
produ ced fr om buffings . whole tire, or stampi ngs. The rubber
hydrocarbon content s hould be between 40 and 50% and should be
r e l a tive l y uniform throughout the ru bber shipment.
If
low
degrees
of interaction occur as ind i cated by
insuffi c ient viscosity increase or l ow elongation, use of rubber
with a smaller particle size , r o ugher surface texture or higher
rubber hydrocarbon or na tural rubber content can inc r ease the
deg r ee o f interact i on.
The gradation of the rubber i s very important when us ing
a spha lt-rubber in ho t·mixe d paving mixtur es. If the rubbe r particle
size i s too larg e f or the vo id spaces within the aggregate,
compac tion difficultie s can occur and mixes can a c t
• spongy · after
compaction.
Since the voids in the aggregate depend on the
spec i fic mix type, different rubber gradations are suited for
different
mix
types. For open - g r aded mixtures , l arge rubber
particles can be used wi thout problems. Dense-graded mix tur es ,
however; requi r e use of fin e r rubber to produce mixes which
compact appropriately. Sugges t ed gradations are as follows:
Sieve Size
No.
No.
No.
No.
No.
10
16
30
80
200
Percent Passing
Open-graded mix
Dense - graded mix
100
75- 100
25-60
0-20
0-5
100
95-100
70-100
0-20
0-5
Rubber Content
The maximum amount of rubber which
can
be
used
in
asphalt-rubber for hot-mixed paving applications is limit ed b~' the
requirement that the asphalt - rubber must be capable of being
pumped, and mixed appropriately with the aggregate. Asphalt-rubber
materials with viscosities of up t o 4000cp at 350 0 F (as indicated
by a Haake Rotational viscometer) ha ve been found to be acceptable
for use in dense-graded mixture s . If viscosities significantly
exceed 4000cp at 350 0 • aggregate coa ting problems during mixing
can result. Higher v i scos iti es (up to 6000cp) have been used with
open-graded
mixt ures
without
aggregate
coating
problems.
Generally. with most asphalts and typical rubber types appropriate
for hot-mixed paving, maximum rubber contents based on viscosity
are approximately 18 to 20% by total weight of the asphalt-rubber
mixture.
The minimum rubber content r equired is based on producing
appropriate consistency at high service temperatures (softening
point) and elasticity (resilience). Increasing the rubber content
provides both incr.eased elasticity and increased high temperature
reinforcement of the asphalt-rubber . Generally , rubber contents of
at least 15% by total asphalt-rubber mixture weight are r equired
to meet reqUirements of Table 1.
Table 2 shows properties of blends of asphalt-rubber at
several rubber percentages. Figure 4 i s a plot of the test data
versus rubber content. Note that f or these combinations. hot
climate properties are met at
rubber
contents
of
between
approximately 16 and 19% rubber. Also note that the mixture
viSCOSity increases rather linearly up to a rubber content of 15%
and then begins to more rapid l y increase with increasing rubber
contents. Figure 4 indicates that a 1500cp viscosity is achieved
with 15% rubber, and that 4000 cp is achieved at 19% rubber , a 4%
range .
An appropriate se le c ti on for rubber content for this
mixtur e would be 17% to provide a mixture in the center of the
viscosity range while meeting other properties for a hot climate
asphalt-rubber. Testing would then
be
required
during
the
additional heating periods as previously discussed.
Int eraction Conditions
The time and temperature cond iti ons for the int e r action
between the ~sph~ lt and the rub ber need to be spec ifi ed because of
the influence on re sulting properties. As previously di scussed, en
i mportant con s i derat i on
for
an
asphalt-rubbe r
materia l
is
stab ilit y
o f pro perties over time per i ods experienced during
construction.
Appropriate
temperature s
f or
asph~lt-rubber
int e ra c ti on er e 350 + /- 25 0 F . In this temper~t ure range , the
int e ra ction generally proceeds quick enough t o r each
desi red
pro per ti es within 30 minutes to 1 hour after blending the rubber
with the a s phalt while pr ov iding adequate property
r e t ent i on
during
ex t ended
heat ing .
At temperatures lower than 3250 F,
int e ra c tion period s whi ch are generally greater than 1 hour are
required
to
achieve d es ired proper ties . Thi s can cause low
prod uction rate s . . Tempera ture s in the rang e of 375 0 t o 42S o F
qui c kly pr oduce des ired propertie s , but may la ck in property
stability d ur ing extended hea ting per iod s. Table 3 shows test data
during a 24 hour labo ratory . intera c ti o n pe ri od f o r a typi c al
asphalt-rubber blend . These data indi c ate a uniform vi scos ity from
30 minu t es of intera c ti on to 24 hours, and adequate s tability of
phys i ca l properties to me et moderate c limate prope rty limits of
Tabl e 1 throughout the 24 hou r intera c tion peri od.
DESIGN OF DENSE- GRADED ASPHALT-RUBBER CONCR ETE
Bo th
Marshall
and
Hveem
methods
(39)
with
sl i ght ·
modi fications
can
be
used
f or
d esign
of
dense-graded
asphalt -ru bber concre t es. Both proced ures e s sentially cons i st of'
selecting
aggregates and binder, compa c ting mix es at varying
binder conte nt s , ana lyzing compacted spec imen voids, mec hanical
t est ing , and then select ing the binder con t ent based on data
ob tai ned. The follo\1'ing dis cuss i ons when us ing a spha lt-rubbe r, can
be applied to both Marshall and Hveem proce dure s .
Aggregate
Dense -graded asphalt-rubber concrete paveme nt s are composed
of
typi ca l
dens e -graded
type
aggregates
and
appropriate
aspha lt-rubber binder . Aggregate should meet the same quality
requir eme nt s as f or conv.e nUonal asphalt conc ret e which would be
us ed in similar applications . Due to the presence of the rubbe r
parti c l es in the asphalt-rubber binder, the aggregate gradation
for dense-graded mixtures should be maintained on the coarse side
of the gradation band. Gradations which plot between the maximum
d ensi ty line and the uppe r limit of the band should be avoided
(Figur e 5). Mai nt ai ning the gradation on the middl e to coarse side
of typi c al d ense-g raded band s i s important t o provide sufficient
void spa ces in the aggregate for the rubber particles. If the
gradation i s too fine, or the rubber particles ere t oo large ,
compaction problems resulting from rubber interference between
aggregate parti c le s can r esult . Thi s effect i s indicated b~' t wo
observations
during
the
mixture
design
procedure.
Fir st ,
immediately ~fter compaction and while hot, the mixture will
appear to have a somewhat unstable and • spongy ' characteristic if
coarse aggregate particles are pressed into the mix. second ", a
r elatively level trend in mixture air voids data will be noticed
with increasing . asphalt-rubber contents , instead of the typical
decrease in air voids. Both of these effects can generally be
reduced and eliminated by coarsening the gradation or by reducing
rubber particle size used. Suggested gradation limits for 3/8
inch, 1/2 inch, and 3/4 inch maximum sized dense-graded mixtures
f or use with asphalt-rubber binder are li sted in Table 4 .
Asphalt-Rubber
The asphalt-rubber for use in dense-graded paving mixtures
should
be
composed of rubber meeting the previously stated
gradat i on 1 imi t s ' for use
in
dense-graded
mixes,
and
the
appr opriate asphal t cement or b l end with extenders to meet desired
physical parameters such as those listed in Table 1.
Tri al Asphalt-Rubber Contents
Due to the replacement of a portion of the asphalt by r ubber
in
the asphalt-rubber (15 t o 20~), generally. asphalt - rubber
contents to be investigated during dense-grade d mixture d esigns
are 15 to 25X higher than asphalt cement contents which would be
used for the same aggregate type. During the de s ign procedure . the
ru bber in the aspha lt should be considered as an integral part of
the overall binder.
During specimen evaluation and analysis , the rubber is accounted
f or
blio'
measuring the asphalt - rubber specific gravity or by
calculating the combined specific gravity of the asphalt and
ru bber blio' propo rtion. With typical asphalt cements
(specific
gravity of 1.00 to 1 .02) and granulated tire rubber (spe c ific
gravity of 1 . 15 -1. 20), the combined specific gravity of
the
asphalt-rubber is between 1.02 and 1.05 at 600 F.
Specimen Mixing
Prior to mixing, it i s recommended that the asphalt - rubber be
heated to 350 +/- 100 F and the aggregate to 300 +/- SOF. The
350 0 F temperature for the asphalt - rubber is recomme nded for each
asphal t-rubber grade in Table I, regardles s o f base asphalt grade
du e t o the specified viscosity of between 1500 and 4000 cpo The
a sphalt-rubber s ho uld be heated in an oven us ing the procedure
contained in Appendix 2 and should be stirred to assure uniformi ty
( approximately 1 5 seconds) immedia tely before adding t o the 300 0
aggregate .
Mixing of the asphalt-rubber with the aggregate should be
performed using standard types of mechanical mix ers u s ing whips or
paddles. Mixing should be performed immediately after addition of
the asphalt-rubber to the aggregate. Mixing should continue for at
least 30 seconds beyond the time required to obtain comp let e
aggr egate coating. Total mix ti me should not exceed 2 minut es. If
complete aggregate coating i s not achieved in 2 minutes (whiCh may
be due to very fine or dusty mixe s) either the asphalt-rubber
content shou ld be increased or a liquid anti-stripping agent
t
~hould
be added t o the asphalt - rubber t o assist aggregate coa ting. ·
Fo ll owi ng comp l et i on of mixing, the mixture should be sp lit int o
appropr iat e po rti ons (approx . 1100 t o 1200 gms ) f or compaction of
spec i me n s . If Hveem compaction will be used , the spec imens should
be sub jec te d to the st anda rd 140 0 F curing pr ocedure for 15 hours .
SpeCi men Compact ion
When usi ng Marshall compacti on , the indi v idua l spec imens
s hou ld be placed in a forced draft oven maintained at 280 + /- 50 F
f or between 1 and 2 ho ur s prior to compaction. Ins ure that the
mixture has r eac hed the compacti on temperature by chec king the
a c tual mix temperature with a thermometer.
SpeC imen compac tion cons i s t s of r emov ing the specimen from
the oven , pla c ing int o heated Marsha ll mo ld s , spading for 1 5
times , and
compac ting
us ing
standard
Marsha ll
procedures.
Compact i on l eve l can be 3 5 , 50 , or 1 5 blows per side as dictated
f or the anti c ipated tra ffic le ve l . Compac ti on should be comp leted
within 3 minutes f o ll owing removal of spec i mens fr om the o ven.
When u sing th e Hveem procedure , the mix shou l d be heated t o
a compac ti on t empe r a tur e o f 280 +/- 50F aft er the c uring period.
Compaction
the n
procedes
using the standard Hveem kneading
proced ur e . Some agencies use a compa c ti on t emperat ure of 300 0 F.
Immediate l y f o ll owing completion o f compact i o n , the specimens can
be eval ua t ed f o r in s ta b ility and ' spongyness '
as
p revi ous l y
dis c ussed. For bot h pr oce dures, specimens should be a ll owed t o
cool off f or a min i mum o f 4 hours pri o r t o r emov ing from th e
mo ld s. The reason f o r this is that if specimens are r emoved whi l e
still warm, d e f o rmati o n due to rebound fr om t he rubbe r particle s
may occur, which cou l d distort r esu lt s.
Specimen Testi ng
For bo th Marshall and Hveem procedures , f o llowing r emoval
fr om the mo ld s , s pec i mens are te s t ed using sta nd a rd procedures to
evaluate stabi lit y , fl ow , stabilome t er value, density, voids , e t c.
Marsha ll Procedure: Te s t r esult s should be r eported
US ing s tanda rd procedures and me thods. The design asphalt-rubber
binder con t en t s hou ld be selected to prov ide a mix ture with a n
app r opr iat e l eve l of air voids
while
prov iding
appropriate
stability fl ow , and V. M. A. a s indi ca ted f o r conve nti onal mixture s
in the MS-2 manual (40). TWo modifications in d es ign c rit e ri a
should be us ed f or aspha lt-rubbe r d ense -graded conc r e t e . First,
due to th e inc reased viscosity , elasticity, and soften ing point o f
the
a sphalt-rubb'e r ,
asphalt- r ubber concr ete mixtur es tend to
experience le ss compac ti on and dens ifi ca ti on from traffi c after
construction.
There for e ,
f o r den se -graded mixtures containing
asphalt-rubbe r binder , the de si gn air vo id leve l can be set at the
l owe r end of the 3 t o 5% range. The targ et there f o r e for air void
l eve l s hould be 3 to 4%.
The second modification
in
ana lY Sis
of
r esu lt s
f or
d e t e rmining design binder content i s that maximum fl ow values can
be rai sed t o 24 f or light traffic , 22 f o r med ium traffiC, and 20
for h e avy traffic due t o the higher bind e r c o ntents which are
typically r equired . An e xamp le of a mix d esign which shows d ata
and r esu lt s for a d e ns e - graded ho t mi x u s ing asphalt - rubber is
contained in Appendix 3 , Typi c al d es ign a s phalt - rubber binde r
contents f o r d ense - graded mixture s range between 6.5 and 7 . 5% b~1
total mixture weight, (7.0 t o B.Il by agg regate weight).
Hveern Procedure:
As with the Marshall procedure . te st
results should be repor ted u si ng standard pr ocedures and methods.
Aspahlt-rubber mixtures generally yield stabilometer values whi c h
are significantly lower than those obtained for convential asphalt
con c rete (31). This may be due to the more elastic behavior of the
compacted
mixtures.
Typic al
stabilometer
re s ul ts
wi th
asphal t-rubber dense - graded mixe s are 20 to 30
wh en
using
aggregate whi c h produces 35 to 40 stabilities with asphalt cement.
For
specification
purposes l i t is suggested that the
aggregate to be u sed be verified t o be ca pable of providing a
minimum Hveem stability which mee t s standard specifications when
using asphalt cement (35 or 37 minimum) . The suggested value f o r
stability when using the same aggregate and asphalt-rubber i s 20
minimum. During specimen evaluation ,
as
with
the
Marshall
pro cedure, it i s suggested that air voids f or the design be
targeted at 3 to 4 percent instead o f the 4% minimum. As with th e
Ma r s hall procedure , t ypi c al binder contents are 6 . 5 t o 7.5% by
total mix weight .
.Mo isture Res i stance:
After the asphalt - rubber binder
content of the mix ha s been determined , the moisture resistance of
the mix shou ld be c he c ked. Conventional procedures
such
as
Irrrnersion
Compression
(ASTM
01075) (37),
Lottman
(40).
or
Tunnicliff-Root (41) can be used. Additives whi c h are used t o
improve moisture r esistance ( l iquid additives , hydrated lime , or
cement).
of
conventiona l asphalt concretes can be used f o r
asphalt-rubber mixture s. Ac ceptance criteria should be the same a s
for conventional asphalt conc rete .
DESIGN OF OPEN-.GRADED ASPHALT- RUBBER CONCRETE
The modified physical properties of asphalt - rubber binder
permit its use . in a variety
of
manners
with
open-graded
aggregates. Due to the higher viscosity of the asphalt-rubber,
very high binder contents (up to 10 or 11%) can
be
used
effectively without experiencing excessive drain off which occurs
with asphalt cement . Use of a higher binder content results in
mixes with thicker binder films, improved aging resistance and
better durability . When using asphalt-rubber binder, high mix
temperatures can be used, again without the drain off problem, to
permit construction in cooler temperatures or at longer haul
distances than with conventional open-graded mixtures. High binder
contents produce mixtures which have crack reflection reduction
characteristics
similar
to
spray
applied
and
chipped
stress-absorbing-membranes (SAM's)
(42) . The design
procedures
which follow generally use methods outlined in the Federal Highway
Administration Report No. FHWA-RD 74-2 titled "Design of Open
Graded Asphalt Friction Courses· (43) with several modifications
to account for the unique properties of asphalt-rubber materials .
The procedures describe methods for determining the asphalt-rubber
content for three
different
types
of
open-graded
mixture
applications. These applications are:
• Normal free draining friction courses at low binder content
• Durable friction courses at a medium binder content
• Plant mix seals at a high binder content
Aggregate
Aggregate
used
for
open-graded asphalt-rubber concrete
should meet the same quality requirements as for conventional
asphalt concrete which would be used in similar applications.
Recommended aggregate gradations are listed in Table 5. These
gradations are typical of many 3/8 and 1/2 inch open-graded
mixtures used throughout the United States. For the 3/8 inch
gradation, overly thickness should not exceed 1 inch . For the 1/2
inch gradation, maximum thickness should be 1 1/2 inches.
Asphalt-Rubber
The asphalt-rubber for use in open- graded paving mixtures
should be composed of r ubber meeting the
previously
stated
gradation
limits
for
use
in open- graded mixtures and the
appropriate asphalt cement or blend with extenders to meet desired
physical
parameters such as those listed in Table 1. Due to the
large void spaces which exist between aggregate particles in
open- graded mixtures , larger rubber particles can be used in the
asphalt-rubber than with dense - graded mixtures.
Asphalt - Rubber Content
The
suggested method for determining the
content consists of three basic steps followed by
for mix type.
asphalt-rubber
an adjustment
Step 1. Determine the surface constant Kc of the aggregate
using the FHWA RD-14-2 procedure (oil soaking and drain off)
(43).
This procedure is also contained in the Asphalt
Institute t-1S-2 manual.
Step 2. Calculate the required asphalt
the following formula: (43)
cement
content
using
Percent Asphalt (agg. wt . ) - 2.0 Kc + 4.0.
Step
3.
Determine
the base asphalt-rubber content by
dividing the percent asphalt from step 2 by the asphalt
cement (and extender if used) content of the asphalt - rubber.
This provides an asphalt - cement content in the asphalt rubber mix which is equivalent to that determined in step 2.
Open- Graded Asphalt-Rubber Concrete Types
Open - graded mixes using asphalt - rubber can be classified
into three basic types depending on the binder content used.
Free Draining Friction Coarse: This type of mixture is
constructed
using
the
base
asphalt-rubber content with no
modifications. This provides a friction coarse which has skid
resistance and draining characteristics similar to a conventional
open-graded friction coarse constructed using asphalt-cement. Use
of the asphalt-rubber binder provides improved durability and
permits use of higher mix temperatures for cool climates. Typical
asphalt-rubber binder contents are between 6.5 and
8.0%
by
aggregate weight. This mix type generally has between 15 and 18%
air voids when compacted using 50 blows per side with a Marshall
Hammer at 275 0 F. An example design is shown in Appendix 4.
Durable Friction Course:
The binder content for the
durable friction course
is
determined
by
multiplying
the
previously determined base asphalt - rubber by a factor of 1 . 2.
Typical asphalt - rubber binder contents are 8.0 to 9.5 percent by
aggregate weight. This mix type has somewhat thicker binder film
thickness which results in increased durability, but with
a
somewhat lessened drainage capacity. This mix type generally has
12 to 15% air voids when compacted using 50 blows per side with a
Marshall Hammer at 215 0 F.
Plant Mix Seal:
The binder content for the plant mix
seal type of open graded asphalt - rubber concrete is determined by
multiplying the previously determined base asphalt- rubber content
by a factor of 1.4. Typical asphalt-rubber binder contents for
this mix type are 9 to 11% by aggregate weight . When compacted at
2750F using 50 blows of the Marshall Hammer per side, this mix
type generally has 8 to 12% air voids. The high binder content
produces a mix with improved aging resistance , durability and
resistance to reflective cracking. When this mix type is placed to
a thickness of 3/4 inch, there will be between 0 . 65 and O.B
gallons of asphalt-rubber per square yard on the pavement which is
typical of 8 stress absorbing membrane type application.
Specimen Mixing
.
Following determining the asphalt-rubber content for the
application , mixtures of the open-graded a spha lt-rubber concrete
are made . The asphalt-rubber should be heated in an oven to 350 0 F
+ / - 100F and be stirred immed iately proir to addition to aggrega t e
in order to insure that the mixture is homogeneous and rubber
particles are not segregated . Proportioned aggregate should be
heated to 300 0 F prior to mixing with the heated asphalt -rubber.
Mixing of the asphalt - rubber with the aggregate should be
performed u sing appropriate types of mechanical mixer s using whips
or paddles. Mixing should be performed immediately after addition
of the asphalt-rubber to the aggregate. Mixing shou ld continue for
at lea st 30 seconds beyond the time required to obtain complete
asgregate coating. Total mix time should not exceed 2 minutes.
Following completion of the mixing , the mix shou ld be split
into 1000gr. portions for drainage testing and appropriate sized
specimens for moisture r eis i stance testing .
Mixture Production Temperature Determination
Testing should be performed in accordance with the FHWA
RO-74-2 drainage procedure (Section 6 . 11 . A temperature of 290 0 F
is recommended for starting the drainage eva luation . If drainage
at 2900 F after both 15 and 60 minutes is acceptable. a mix
production temperature of 290 0 F + / - l OoF can be used. If excessive
drainage occur s . lower temperatures should be inves tigated unti l ,
appropriate drainage levels are obtained . The appropriate drainage
l e ve l i s defined as no more than a s li ght puddle (l ess than 1/4
inch diameter at points of contact between aggregate and the glass
plate.
Moisture Resistance Testing
MoistUre r esistance of the mixture s hould be determined in
accordance wi th standard t est ing methods u sed f o r open-graded
mix tures such as Immersion Compression or 24
hour
Marshall
Imme rsi on.
Immersion Compress i o n:
Testing
should
be pe rformed
u s ing ASTM D 1075 procedures (371 . Mix compac tion temperature
should be the previously determined mix t emperature, and molding
pressure should be 2000 psi instead of 3000 psi (4 31 .
Marshall Immersion: For Marshall Immersion
testing,
specimens
should be compacted after cond iti oning at the mixing t emperature
f or 1 to 2 hours. Specimen compact i on should be 50 blows per side
of the Marshall hammer and compac ti on shou ld be comp l eted within 3
minutes after r emoval from the oven .
DESIGN OF GAP-GRADED ASPHALT-RUBBER CONCRETE
Gap-graded asphalt-rubber concrete mixtures are a variation
of dense-graded ' mixture s in which the aggregate gradation is
coarsened to provide a greater amount of mixture voids.
The inceased voids permi t use o f an increased asphalt-rubber
content
to
provide
increased
mixture durability . Suggested
aggreg ~te grading limits are shown
in Ta ble 6. Aggregate should
me et
normal
other quality requirements f or asphalt concrete
aggregate s . Asphalt - rubbe r should be of the appr opriate
type
listed in Ta ble 1 and shou ld use the dense-graded type of rubber.
Th e
Marshall de s ign pro cedu re for dense -gr aded mixtures
whi ch was di scussed previous ly can be used for the design of
gap-graded asphalt-rubber conc retes. During the de Sign. it is
suggested that air void levels of 3 to 5 percent be achieved .
Additi ona l criteria li sted in the dense-graded design procedure
should be met except that flows can be raised to 26. 24. 22 f or
light. medium and heavy traf.fic.
Gap-graded mixtur es which have a mor e open gradation which
approa c hes an open-gr aded mix can also be used. As the gradation
is opened , greater amounts of asphalt-rubber binder are required
t o produce 3 t o 5 perc ent air voids, and the mix will take on
chara c teristics closer t o an open-graded mixture.
Typical binder contents for gap-graded mixture gradations
listed in Table 6 are between 7 . 0 and 8.5% by total mix weight.
Suggested thicknes s limits f or 3/8 inch gap-graded asphalt - rubber
mixture s are 3/4 to 1 1/2 inches, for 1/2 inch mixtures, are 1 to
2 inche s , and f o r 3/4 inc h mixture s . 1 3/4 to 3 inches. If
gap-graded mixtUres with more open gradations are used , maximum
thi ckness should be reduced.
ASPHALT-RUBBER CONCRETE MIX PRODUCTION
Equipment
Asphalt -rubber concrete can be mixed in either batch or drum.
type pr oduc ti on plants. It i s suggested that in order to prevent
c ontamination of the storage tanks, and to prevent segregation of
the asphal t-rubber, that a sepe rate asphal t-rubber storage tank
with a ppropriate 8gitati on be used. Additionally. it is sugge s ted
that a seperate asphalt-rubber supp ly system equiped with a pump
and mete ring system capable of adding binder t o the aggregate at
the correct percentage tbe used. Asphalt-rubber binder content
should be maintained within plus or minus 0.5 percent of the ·
de sign value f or ~ingle test value s.
Mixture Produ c tion Temperatures
suggested asphalt-rubber temperatures when being added to
the aggregate f or all mi x types are between 325 and 375 0 F. For
dense and gap-graded mixtures it is recommended that the aggregate
temperat ure be 290 t o 3250 F . For open-graded mixtures, aggregate
temperatures should be appropriate to r esult in the lob determined
mix temperature.
CONSTRUCTION TECHNIQUES AND GUIDELINES
Asphalt-rubber mixtures are hauled, placed, and compacted
using convent i onal equipment and s lightly modified techniques.
When hauling asphalt-rubber mixture s , truck bed s should be sprayed
with a water-soap, solution or dilut e silicone emulsion instead of
kerosene or diesel fuel. Kerosene or diesel fuel shou ld not be
used because o f an affinity f or absorption into the
rubber
particles whic h can result in mix tenderness.
Mixture laydown temperature s should not be be low 250 0 F for
open-graded mixtures or 275 0 F for dens e-graded or
gap-graded
mixtures.
Asphalt-rubber
mixtures
should
be
compac ted
using
stee l-wheeled rollers. Pneumatic rollers should not be used due to
an inc rea sed adhesiveness of the asphalt-rubber binder, which can
stick t o the rubber tires . Compaction should proceed quickly 8S
soon as the mixture is capable of suppor ting the r o llers without
excessive
shoving.
Delays
should
be
avoided
because
8S
asphalt-rubber mixture s cool , they become mo r e
difficult
to
compact due t o the reinforcement provided by the rubber. Figure 6
shows lab d ens ity data obtained f o r dense-graded mixtures made
with 120 and 60 pene tration asphalt-cement, and asphalt-rubber
made fr om the 120 penetration asphalt and 18% minus 20 mesh
rubber . Note the reduced dens iti es of the asphalt-rubber mixture
in comparriso n to the aspha lt cement mixtures as temperatu re drops
fr om 275 0 F to 2000 F.
Open-graded
asphalt-rubber
mixtures should be compac ted
us ing a minimum of 3 full r o ller coverages. Dense and gap-graded
mixture s should br compac ted to provide a minimum of 95% of the
lab compacted density. Vibratory r ol lers can be used with dense
and gop-graded mixtures, but shou ld not be used for open - graded
mixtures .
With some asphalt - rubber concretes at high binder contents,
the compacted mix may exhibit excessive stickiness just after
construction. If this occurs , it is recommended that a light
application (approximately 4 l bs. per square yard) of blotter sand
be use to alleviate the problem.
S~~RY
This paper covers design methods which can be used f or
hot-mixed
asphalt- rubber
concrete
pavement s .
Properties
of
asphalt-rubber binders appropriate for use in hot- mixed paving
mixture s
are
discus sed
along
with factors which influence
asphalt -rubber properties . Criteria for selecting the specific
asphalt-rubbe r formula and specifications
for
us e
in
hot,
moderate, and cold c li ~tes are pre sented .
Mixtur e design methods for asphalt-rubber dense, open, and
gap-graded
mixtures
are
dis cussed .
Each
method
foll ows
conventional Marshall, Hveem, or FHWA procedures with sugsested
mod ifications to incorportate asphalt-rubber binde r. The methods
presented can easily be performed by most l aboratories profi c ient
at asphalt- concrete mix designs with aquisition of mino r pie ces of
additional equipment. Evaluation c riteria and suggested property
limit s for both the asphalt~rubbe r and asphalt-rubber concrete
mixes could possibly be used as a basis for establishment of
uniform constru ct i on specificat i ons.
Table 1 Suggested Phy s ical Prope rty
Limits f o r Asphalt-Rubber Mat erials f o r
Use in Hot-Mixed Asphalt Concrete Appli ca ti o ns
Property
Ho t (2)
Climate
Property Limits1ll...~~,-_
Mode rat e
- Cold
Climtlte
Climate
Viscosity . Haake , 3 50 0 F
1500- 4000
Softening Poi nt, (ASTM 036)
130°F min
Cone Penet rati on , 77 0 F
(ASTM 03407)
20-60
Resilience , 770F (ASTM 03407) 20% min
Ductility , 770 F (ASTM 0113)
15 cm/min
Low Temperature Flexibilit y 3
(ASTM C711 modified)
l500 -4000Cp
120°F min
1500-4000c p
ll OoF min
50-100
10% min
15 cm/mi n
80-150
0% min
15 cm/mi n
15° max
No te s :
1) .
Prope rty limit s shou ld be s tipulated at a spec ifi c int e r ac tion
peri o d such as 60, 90 , and 120 minutes.
2).
Make c limate se l c tion ba sed on the following
tempe rature
ranges
from the U . S . Department o f Comme r ce Enviromental Data
Servi ce . Ho t c li mate - average July max - 110 0 F-; average Jan. l ow
30 0 F+ . Moderate Climate
average July max - 100 0 F- ; average Jan.
low - IS-30°F . Cold Climate - averag e July max - 80 0 F-; average Jan.
low
15 0 F- .
Make the sele c ti o n based o n January low, the n check
Jul y t emperatures . If July temperature s exceed those o f the grade
selected based on Janua r y temperatures , use the n ext stiffer grade.
3).
As an alternate, Cone Pe netration at 39 . 2 o F . 200g. 5 sec . can
be u sed. Limits would be 10 min. for hot c limate, 25 min. for
moderat e c limate , and 40 min . for co ld c limate.
Table 2 Physical Properties of Asphalt
Rubber Blends with
Differing Rubber Contents
Per cen t Rubbe r (Mix BASis)
~
_6_
.L
...JL
...ll..
...ll..
--.l.L
Viscosity, 350 o F, .c p
60
550
aoo
900
15 00
2500
6000
Cone Penetration,77 o F
4a
40
43
40
30
27
Resilience , 77°F
-1
-1
12
19
23
.0
47
Softening Point . F
122
126
136
140
142
146
162
Prope rty
.
Notes:
1).
Asphalt is AC-2 0 , rubbe r is minus No. 16 mesh.
2).
Intera c tion period is 90 minutes at 3500F.
Table 3 Asphalt Rubber
Test Data During B 24 hr
Inter action Per i od
TE ST PERFORMED
Vi scosi t~" Haake
in centipoise
@
30
min
60
min
2000
2000
Interaction Period
90
120
min
6 hr s
min
24 hrs
350°F
2200
2200
2200
72
69
67
65
Re sil ience 0 77°F in
% rebound
17
20
20
23
Duct ility, 77°F 5 cm/min;cm
2.
21
25
32
128
128
129
Penetration, Cone
in 1/10 Illll
@
2200
77°F
Softening Point in of
122
Fra c ture Temperature
127
128
OF LOUIest Passing
,.
12
12
of Fracture
12
10
10
Notes :
1).
Asphalt cement
Point • llOo F.
is
AC - 5 ,
Penetration
(05)
198, Softening
2).
Asphalt Rubber Blend is 83X AC - 5; 17% 20 mesh rubber.
3).
Interaction temperature is 350° F.
4).
6 hour to 22 hour holdover temperature is 300°F.
Table 4 Suggested Gradation
Specifications f o r De nse-Gr aded Asphalt
Rubbe r Co nc rete (Per cent Pa ss ing)
318"
Mix Desi gnation
1 /2"
3/4"
125 . 0 1lIJl)
100
100
100
119.0
IlIJl )
100
100
90 -1 00
1/2" (12.5
IlIJl )
100
Sieve S i ze
1•
3/4
90-100
70-90
3 /8 " (9.5 rrm)
90-100
75-95
60-80
••
(4.75 rnn)
60- 80
50 -70
40 -60
#8
12.36 1lIJl)
4 0 - 60
35-50
30 -4 5
# 30
( 600-um)
18- 30
15 -25
12-2 2
#5 0
(300- um)
8-18
6 -1 6
5-14
2-8
2- 8
2-6
#200 175-um )
· Table 5 Suggested Gradations for
Open- Graded Asphalt-Rubber Concrete
Mixtures (Percent Passing)
Mix Desisnation
Sieve Size
3/B"
1/2"
3/4 " (19 . 0 om)
100
100
112" (12.5 ITJlll
100
95-100
3/8 " (9 . 5 nm)
85-100
75-95
#4
(4.75 om)
25-55
20-45
#8
12.36 nrn)
5-15
5-1 5
#30
(600 urn)
0 -1 0
0-10
0- 5
0-5
#200 (75 urn)
Ta ble 6 Suggested Gradation
Specifications for Gap- Graded
Asphalt-Rubber Concrete (P ercent Passing)
Sieve Size
3/S"
Mixture Designation
3/4"
1/2"
(25 .0
lIlll )
100
100
100
3/4" (19.0
lIlll )
100
100
90-100
1 /2" ( 12. 5 mm)
100
l'
3/S" (9.5 JJJTl)
90-100
65 - S5
90-100
70-90
50 - 70
#.
(4.75 mm)
50-65
35-50
30-45
#8
(2.36
28-40
20-32
16-28
#3 0 ( 600 urn)
12 - 22
8-18
6-16
# 50 ( 300 urn)
6- 16
5- 14
4 - 12
3-7
2-6
2- 6
lIlll )
#200 (75 wn)
.,
z
0
"~
<
J.~-l'- Ae-7.S .. HI> in I:lou nder
and 111 ...bh ..
"
"
r-.....r--...,I- AC-7.S
of
u%
AC-l.S "lIh 7: b,e ndc r
and 111 a"bb ,..
u.t.
30
0
z
••
0
0
"
AC 1.S
20
w
•
IIC-7.S -+ lI..bber
"
"
s
AC-20 + lubber
,
AC-20
,
2 .
J
,
s
TIME, HUWT£S
,
• , "
FIGURE 1.
Constant Load Creep Plo ts For Asphalt Cement
And Asphalt-Rubber At 39F With A 500 g. Load
FlGURE 2.
Constant Load Creep Plo ts For Asphalt Cement
And Asphalt-Rubber At 74F With A 25 g. Load
'\C-20
"
"
"
"
•
;: "
•
~ "
"• "
,
AC- ',) v 1th 14% l>tund cr
a nd 11% ."bbu
0
AC7.5 Wi t h 7%
~
-
and
l>tt~nder
171 Rubber
u
~
.0
, , • , • , •
0
0
,
.0
Tna::, KIh11Tts
FIGURE 3.
•
.>0
.60
... !So
•
"" ,
§
~
s
"
k£!iILItHCt
•
"
"-,
-i!
140
"g
.. 130
~
•
~
"
E
~
o
l:
Constant Load Creep Plots FOT Asphalt Cement
And Asphalt-Rubber At IOCF With A 1 g . Load
~
l
SOF'TENINC POIHT
-
~
~
<
120
~
§
•
>
110
o
VISCOSITl
0
0
FIGURE 4.
l
•
,
.,
.,
••
Properties Of Asphalt- Rubber Blends At Various
Rubber Contents (Data From Table 2)
,.
"
<
•
C!V.DATlON AREA
TO AVOlD
o
•
;;;
D
••
••
•
•
..
S IEVE S lI [
0 . 4) POWER
FIGURE 5. I l lustration Of Gradat i on Area To Avoid With A
Typical Dense-Graded Gradation When Using
Asphalt- Rubber Bi nder
AC-1.~
(120 pell.)
'"
AC-20 (60 pell.)
'"
E
§
lJ~
Collpaotin Illort • B/l~ 11..., ~nhd l
" ' +---------.---------r--------r-------:~
2H
)DO
m
'"
Figure 6.
'"
COKPACnO); TD!Pf:lATtlll , t
Variation Of Density Of A Dense-Graded 1/2 "
Mix With Asphalt Cement And Asphal t-Rubbe r
When Compacted At Temperatures Ranging From
From 200F To 300F
APPENDIX 1 Procedure For Lab Interaction
or
Asphalt-Rubber Materials
The r ecommended procedure for preparing a spha lt-rubbe r materials
in the la bo ratory consists of subjecting the asphalt-rubber to
temperatures and times which will occur in actual use. The mixture
is then tested at several specifi c points in the interaction
period to evaluate the properties of the mixture d uring norma l
application period s . The procedure for preparing a spha lt - rubber
is a s follOlJ!s :
1). Selection of asphalt cement. rubber, and additives for the
mixture.
2) . Selection of the proportions of each material to be te s ted.
3). The asphalt cement.extender (if used) and adhesion agent (if
used) ar,e placed in a standard 1 gallon open top metal can.
Approximately 2,000 grams of the blended materials should be
used. The materials are then heated us ing any convenient
met hod to 50 +/- 10F above the desired tempe rature to be used
during the intera c tion period. During heating, the materials
should be stirred to insure uniformity.
4). All of the granulated rubber to be used in the mix is then
added to the heated esphalt cement end stirred in using an
appropriate hand stirring devi ce (spatula) for·opproximately
30 seconds or until ell of the added rubber is wetted into
the asphal t.
5). Th e mix ed material is then placed in a forced draft oven
maintained at an appropriate tempe rature to ~intain the
desired interaction tempera ture (typically approximate ly
25F above the interacti on temperature). Th e container
should be loosely covered .
6). After 15 minutes has elapsed, after th e rubbe r has been
added, the container is removed from the oven, then stirred
b!.' hand for 15 seconds, and then repla ced in the oven.
7). The sample is then sUrred for 15 seconds . aiter an
add itional 15 minutes, and then is stirred at 30 minutes
intervals until 2 hours has elapsed. During this time
period, while stirring, the temperature should be checked
and recorded so that adjustments in oven temperature can
be made, if required to keep the sample temperature within
plu s or minus lOF from the desired interaction temperature.
8). From 2 hours to 6 hours of interaction the sample is stirred
at 1 hour intervals.
9) . After 6 hours of interaction. the oven temperature is
reduced to 300F Bnd the asphalt rubber sample exposed to
the 300F temperature until 22 +/- 1 hours ha ve elapsed since
the rubber was added to the ftsphal t. The asphalt rubber is
then stirred by hand for 15 6econds, replaced in the oven,
and then the oven temperature is raised to raise the tempe rature
of the asphalt-rubber to the interaction temperature within
2 hours. This completes the interaction period.
APPENDIX 2
ReCOIflmendf'd Procedure for Preparing
Samp]M pf AfiDbalt Rllbber fpr Testing
Intrpductjon ;
This procedure recommends methods which should be used for preparing
mixed samples of asphalt rubber obtained from jobs or suppliers for
laboratory use in asphalt concrete mix design, chipseal evaluations,
or other testing procedures .
Asphalt Rllbber Preparation for Testing;
Heating ; The sample of asphalt rubber should be placed in an
appropriate metal container, no larger than 1 gallon (a standard one
gallon round open top paint can ie suitable). The can i6 then placed
in an oven . (preferrably forced draft) maintained at 25 F above the
temperature the asphalt rubber is to be ' heated to. For example if
the asphalt rubber i8 to be heated to 350 F, the oven temperature
sh ou ld be 375 F. Higher temperatures should not be used due to the
possibility of over reacting the rubber components. The can containing
the asphalt rubber shou ld be covered while heating in ' the oven, After
the material has been in the oven approximately 1 hour, the can shou ld
be rem o ved and the sample stirred for 15 seconds, At this time, the
sample will not be totally melted . The can is then replaced in the
oven, covered, heated for an additional 3 0 minutes,
removed and
stirred for 15 seconds again. Temperature is then checked with an
appropr iate thermometer. This procedure 16 then repeated until the
sample is uniformly melted and has reached the mixing or application
temperature . For a 1 gallon sampl e it will take appro ximately 2 1/2
h ou rs to rea ch 350 F.
APPENDIX 3
1.
Aggregate -
Example Dens e-Graded Aspha l t-Rubber Concrete
Mix Design Marshall Method
Crushed Limestone
ilLom
,
'"
l/< ~
lJlo.o
,.
JIB"
," 0.
••
,"0.
"
No..
~o
l! ~"1.1t
,
'"
. •
•
t"
--
"
2~ ",
,.
" .
...,,, AA.! I> 1
,
'",
I
" ...'IrRIAl.
I
25% 1/2 ".
2.
As phalt Cemen t
AR- I.000 .
3.
Gr ound Rubber Gradation
•
".
Kll
to~'U.
sne IrI tA'II OI\
"'"
1 0~ \
H".O
100.0'
93.0
1 0~ . 0
100.0
U . l\
!'S ~ lO~ 1
~ 0. 1
,..
l OO . ~
100.0
e5.] ~
f:>-~~ '
~~. ]
1 00.0
U.l1
~ ~-n \
' .0
!.l
8 B.]
U.l I
l ~-S~ \
U
...
~l.
"
If-!!\
I
] .~
]
](.
S.B'
1 0.S
: .t "
' .~ 'H
~.
'-'
'.1H. 4
~ .,~ , <;>
] .O~ \
l.~;lI
"
l.J .,
.uS ~ tJ· 'IIOl>
.",
1.5% crushed sand
~.O
1.1
".
". "
30% 1/1. -3 /8" .
4- f'
.
f.3 9;>
Penet r ation .7 7F (D5) - 1.9; Softening point (036) - 120F
S j .. ,, ~ Siu
,,,
Rubbu
Cudot1on
100
100
,,,
,,,
1100
11.6
1100
I,,
4.
Phys i ca l Pr opertie s of As phalt- Rubber (1 6% r ub ber ,
'n51
"
PDU'O~
Vi. c~. J ty .
0
HI.ke . t
) )0 ,
i n c ltntipo i u
"'"
Pennrn i on , Cone , "of
1n 1/ 10 mo.
bl1 1h nc e
1 u bovn d
..
."
!!'
.,00
l1Q
• '"
'" '" '" '" '" '"
" " "
" " "
fr , cl ure Te_plt T, luTe
" r l.o~~H Pu~ ln,
0, ,,,nUT,.
Aspha l t.-Rubber Concr e t e Mix t ure Results
Mix Temp . - 300F ..'
l ult
3D
Or
A.fl t!
iii •• •
Sp
g t. .
50/50 Blow Marsha ll
Compac t i on Temp • - 275F
~ I J I D !!
AI Sl e l DAT I SQK KIBI
..,
tr
' uCl
hid.
..,.
2.
~. ~
..
u ~.,
,.,
1.""
1.
~ "H
2. 'H~
1 ' '1 . 5
1 .1 '
T ,S!
1 , " 1"
1 • • '. '-1
n"' . ~
J. n
'.'
, • • n .. ,
1 • • ..,..
I ~n .
'.0
.\1 00
"
Sohlt nl n,. ' Ol M i n " ,
I
" OO
" " "
) <:.'.In.
'1 .. ,. ~·
~
" " "
71"'1
, ull ed , f.ll ur l ,
'u L .p.1.
!.l!.!
'"'' "oo
Du< ~ 111t y f 11°, i n ca
5.
350F intera c tion
a s ph al t )
I
t.M
U. O'
-
J.:,
J
't
15 . 1\
IS .D'
n . ~'
~rr. " t.l
...
lin " " · I
ShUlIt,
(PPll n", )
•••
,.,
,
,
2 . ~~
'0"",
21 H
Recommended asphalt -rubbe r bind er con tent i s 6.5%
6.
Mois t ure Res i s tance Results (r efe r ance 41 procedure)
U~ :oo;D "' ''''tn U t e • •. ""
''' .
. ~h 51:
~" hl "~
,.,.1'
' u . l1 ~
,,,,,,,,h. p.I
no
Itf
j
n.
I. •
I. )
" D 'J1 U ~t
h .
I
,-
eOHI>JT JOn D
'~ h
IL
;.lt1J
~
"-"""""""T.77:1
h .
~
l U :,U
" ,u ~Th
A"
D u. I
SPEC' MtH
Ii.,.,
, . Id
u lo. , . ~ <
,
U !d
s .. ~ r. '!c~
1.6
1. 1
) 0.)
1/.1
~ S.I
I. i
It. ,
!l ••
II .1
I.)
" ,1<.
n .
IP . '
r u. lI.
St ,. nq,~.
"
lu,
10.
I X. ,
' U",
.-
'M l
...
rl . ..
11IIQ Q
p. j
"
"
"
APPENDIX 4
1.
Aggregate
Exampl e Open-Graded Asphalt- Rubbe r Concrete
Mixture Des i gn f or Free- Draining Friction Course
Crus hed siliceous gravel
,"
,-
»
,
,
...
. 00
n .'
.~
. 00
••
·
,.,
'.
t
..
"
".0
It
t6.J
I .l O
11 . 1
•••
n.
<0 .
101 11J~''
S;..
. :-. ~
...
2.
,
.u. 1C>)JI I O~
Asphalt Cement
,
' l .l
n.7
n .'
".6
ll. J
'0.0
u-
7~
U .I
u-
20
29.'
••• •••
••• •••
,..
,..
•••
...•••
I
J. tl"
"
J.111l
'-'
AR- 2000
Penetration , 77F , (ASTM D5) • 66
Softening Point , (ASTM D36) • 11 7F
3.
Ground Rubber Gradation
%Pa.ssing
.10 ... II ..
..,
.n
......
..
.~
.~
.. 00
~
IH OC
. 00
". J
)l . t-
ll.'
..,
'-'
..,
•••
4.
Physical Properties of Asphalt-Rubber (18% rubber, 82% asphalt),
350F Interaction Temperature
l!!
nSf n U'OIUI!:D
~
,- ,-
'fnmsllY . IlAAA1: .u »0 0,
IN CU1'lr01U
"
~~
,,,.
pn. tTu.TI~,
COQ:' nO,
"
kl.IiIUUCl ,
n"T U
»
a Illo _
-. -
i b : !'
m
"
»
,~ -
IOno;1': 1VlIrt n
5.
'" '"
" "
" "
'" '" '" '"
.""
or
n,t,quu. nWIUTUJJ:
0, l,.(lI.·tST 'M5 1~ C
Cl f
"
"
.../ . ,..
1lUcrl1.1lY • n"T U ...
PlAUD • fA1LllU •
)
h..
nAt'f\/J:[
Asphalt-Rubber Content Determination, FHWA Procedure (Reference 43)
0... Dr'd ~h ""'~'
100.0,
OU SOh •• , •• eD<I Drd .... _ I " ,
101.0
"""HU' S.I'. oJ " ". . . . . .
1 . 711)
' .... .... 1.... h « ... (l.71Il/l.Io5 )
1.01
, .~
h.f.. o """.10.'
,.,
(Le)
7.U
Base asphalt-rubber content - 7. 56%(by aggregate, 7 . 0% by mix)
Binder Contents (Mix Basis)
Free-Draining Friction Course
Durable Friction Course (7.0 x 1.2)
Plant Mix Seal (7.0 x 1.4)
6.
Drainage Evaluation at 275F,
lOOn,
7.0%
8.4%
9 . 8%
FHWA Procedure (Reference 43)
0011. VCI'J .lI,h, _ , "f ... Ifto,~ .... 010 ...."" . . . U . ft. '0 .10 .
11.. 1 _ ,lou
I ...
1ft' .1 . . . . . . . f 10 . . . boft
~ hth .
.
_"h, ....
<_'oc' , ..
7.
Density .nd Air Voids of Compacted Mix
'1:!<I ... n
,
•
JI~.
I."
".14.
HoU .....
1.'141
1.UU
11,, 4
14 ••
l.''l ~
1.24H
Ill. l
n.'
2.1414
110.4
14.'
... • • 1Iy
--1.9190
" ..... p
8.
s.c.
l un I.C .
I.
tulk ' 1'«111< , •• vit1 duen.h .. d ... 1. , p ...nth .... Id spul_ •••
1.
til> too.;. • • )O(IT, c~.C<!Oft ' "'I'_ - 11~r.
),
Coopo<tlcn. ) O/~O blo,' )'~nh.ll.
4.
'"phal< r.bb~ r <_.u • • 1.01 ( ...I> •••10).
Mois ture Resistance Evaluation,
Marshall Immersion Procedur e
"""SllT>.! C('J!.;1!1l'(:t.'tP
S nCU~[!'~
5pecl...
IIn.boli
Ip<el. . .
I'... .. b.ll
IIor oboll
,'"
S, . .. II H Z
----1!£,_
$~I>.!!.ll:.
~
...
"
~
,!.wr., .
, .. bUltl bUo •
~.
"
"
. 00
H.~
~7l
1f00U,
l.
1.
l.
4.
Spec I_no oll ,""".IB.d 71 (.I> b .. ,.) .. phalt ..... bb....
H.I> " "'P . • lOOr, <.,....o« t "" •• ~.
27}r.
""-PooUem. $0/ ) 0 "" ,,"oll.
""'01.," <_dI U ... lol ...... h • • d 01 • 24 bOUT . ... k .. 1'0 ' I n . .... .
REFERENCES
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Properties of Asphalt -Rubber Mixtures
Basic
Material
Behavior " Report No. ADOT-R 5 -14 (1 62 ), Arizona Department of
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2.
Pavlovich, R . D . • Shuler, T . S. and Rosner , J. e. , ·Chemical
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Spec ificati ons
and
Te st
Procedures ·,
Report
No.
FHlJJA/AZ-79/121,
Arizona
Department
of
Transportation , November 1979.
3.
Rosner, J.e., and Chehovits , J.C.,
· Chemical and Physical
Sunmary
Properties of Asphalt - Rubber Mixtures-Phase
III
Report and Volumes 1-5, Report HPR 1-19 (159). Arizona
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4.
Piggot, M.R., and Woodhams , R.T . , "Recycling of Rubber Tir es
in Asphalt
Pa ving
Material s '
Department
of
Chemical
Engineering and Applied Chemistry, University of Toronto,
Toront o, Ontario , March 1979.
5.
Oliver , J . W.H . , "A Critical Review of the Use of Rubbers
Polymers
in
Bitumen and Paving Materials ", Report
1037-1, Australian Road Research Board, 1977.
6.
Oliver , J.W.H.,
"A Limited Laboratory Evaluation
of
a
Bituminous
Plant Mix Material Containing Sc rap Rubber" ,
Report AIR 178-8 , Australian Road Research Board , 1976.
7.
OliVer, J.W.H. ,
'Pr elim inary Investigation of the Elastic
Behavior of Digestions or Comminuted Type Tread Rubber in a
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8.
Shuler , T.S.,
"An Invest igation of Asphalt-Rubber Binders
for
Use
in
Pavement Construction" Ph .D. Dissertation,
Graduate School , Texas A&M University, College
station ,
Texas , August, 1985.
9.
Oliver , J.W.H .,
"Modification of Paving Asphalts by Digeston
with Scrap Rubber ", T R R 821, Transportation Research
Board , Washington D. C . , 1981, pp.37-44.
10 .
Schuler, S., Adams, C., and Lamborn , M. ,
"Asphalt-R ubber
Binder Laboratory Study", Res earsh Report FHWA A/TX-85-71 +
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Coll ege
Station,
Texas,
August, 1985.
11.
Lalwani, S., Abushihada , A., and Halasa , A. , "Reclaimed
Rubber-Aspha l t Blends Measurement of Rheological Properti es
to Asses Toughness, Resiliency , Consistency , and Temperature
Sensitivity ", PROCEDINGS. AAPT, Volume 51, 1982, pp. 562-579.
and
A1R
12.
Way ,
G. , 'P reve ntion of Reflective Cracking in Ar izona
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13 .
Ol se n, R.E.,
"R ubber
Asphalt
Bind er
f or
Seal
Coat
Construct i on" , Federal Hi ghway Administration I mp l ementati on
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14.
Huffma n , J.E . , "The Use of Ground Vu l canized Rubber in
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15.
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1978",
Repo rt
No.
1979
GG3 ,
Arizona
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16.
Schnorme i e r, R.H . , " E l even -Ye~r Paveme nt Conditi on Hi story
of
Asphalt-Rubber
Sea l s
in Phoenix, Arizona", Aspha lt
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17.
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18.
Morr is,
G.R ., and McDonald C.H., "Asphalt-Rubbe r St r ess
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1 9.
Verdos , P .,
"Evaluat i on o f the Effe c tiveness of Membranes
f or Pr eventi on of Crack Ref lection in
Th in
Overlays·,
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Scottsdale , Arizona , May 7-8, 1980 .
20 .
Schnormeie r, R.H. , "Fifteen Year Pavement Condition Hi story
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at
1986
Meet ing of the Transportat i o n Re search Board,
January , 1986, Washington D.C.
21.
Epps, J.A . , and Gal l oway , 8 .M . ,
Asphalt -Rubber
User -P rod ucer
Scottsdale, Ar i zona.
22.
Epps , J.A ., Editor ,
Proceedin~s .
Nati o na l
Seminar
on
Asphal t-Rubber ,
Fed e ral
Highways
Admini strat i on ,
Demons trat i on Projects Divisi on, San Ant onio, Texas , October
27-29 , 1981.
23.
Chen , N.J ., DiVito, J.A ., and Mo rri s , G.R . , "Finite Element
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to
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24 .
Coe t zee . N. F . , and Montsm it h , C. L., "Analyti ca l Study of
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Minimization
Ove rl sys
by
Use
of
a
Rubbe r
Asphalt
Interlaye r " ,
Transportati on Research Record 700, 1979, pp .lOO -1 08.
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May
7 8,
Work shop ,
First
1980 ,
25.
McCullogh , F . R . , and Foppe, L . E., "A Five Yea r Evalua ti o n of
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Cur ve
in
Phoenix', Proceedings AAPT , Vol. 54 , 1985 , pp.76 - 90 .
26.
Jimenez , ·R . A. , "La boratory Measurements of Aspha lt-Rubber
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Mixtur es ',
Transportation Research Record 843 ,
1982 , pp . 4-11.
27.
Crit e ria f o r Aspha lt - Rubbe r Concrete
in
Civil
Airpo rt
Paveme nt s ,
OOT/FAA/PM86/39.11 ,
Program
Engineering
and
Ma int enance Se rvi ce , Washington , D. C ., 20591.
28.
Stephens , J . E. , and Mokryewski ,
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Connec ticut, March 5, 1974.
29.
Stephens, J.E.,
"Fi eld
Evalua ti o n
of
Rubber
Modifi e d
Bi t umi n o us Conc re t e ", T.!.!:r~.~n~s~p~a~r~t~.~t~i~a~n,--~R~e~s""e"aIr~c~h,---~R~e~c~a~r~d,,--,,8~4,,3 •
198 2 . pp.11-21.
30.
DeLaubenfels, L.,
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31 .
VanK irk. J.L . , "The Effec t
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of
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32.
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with
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Asphalts " ,
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33.
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34 .
Hugo , F. , and Nachen iu s , Rheinard ,
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35 .
Va l1 erga , B.A.,
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october , 1981, pp. 209 - 2·18.
36.
1987 Annual Book of ASTM Standard s, "American Soc ie ty
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1987 Annual Book of ASTM S tandards ,
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1988 Annual Book o f ASTM Standard s , "American Society f or
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"American
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for
39
'Mix
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40.
lottma n, R.P.,
'Pr edicting
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As phalti c Concrete ", NCHRP Report 192. 1978.
41.
Tunni c liff.
D.G .•
and
Roo t, R.E.,
f o r Effe c tivene ss of Anti-Stripping
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42.
The
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Damage
to
"Test ing Asphalt Conc ret e
Additive s ',
Proceedi ng s ,
Val1erga . B.A., Morris. G.R., Huffman. J.E "
Huff. B. J.
"Applicability .of Asphalt-Rubber
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in
Reduc ing
Re fle c tion Cracking , Proceeding s . AAPT, Volume 49, 1980,
t
pp.330 -3 53.
43.
Smith ,
R.W..
"DeSign
of
Courses ',
Federal
Highway
FHWA-RD-74-2. 1974 .
Open- Graded As phalt Fricti o n
Administration
Repor t
No .