Page 1
Crumb rubber modified bituminous
emulsions. CRE-emulsions
Nuria Querol Sola and Emeline Marty
SORIGUE Ctra. C-12 P.k.162 PO 25.600 (Balaguer) Spain
[email protected] [email protected]
ABSTRACT. Nowadays crumb rubber is one of the major environmental wastes. One possible
way to reuse this waste could be in the formulation of modified bitumen emulsions.
The main objective of the study is to formulate crumb rubber modified emulsions with high
storage stability, improved properties than conventional emulsions and better properties than
polymer modified emulsions formulated with SBS.
For its manufactured we did not use a colloidal mill, instead of that we used a system known as
HIPE ( High Internal Phase Emulsion) where we work in laminar regime with inversion phase,
high viscosity, low revolutions and low temperature and for the internal phase.
This paper summarizes the manufactured conditions used to formulate this kind of new
emulsions as well as its main characteristics. The study was conducted comparing different
modified emulsions formulated with conventional polymers such as SBS and modified
emulsions formulated with crumb rubber.
In conclusion we can say that a new generation of modified emulsions formulated with
crumb rubber is possible. They have high storage stability, improved properties over
conventional emulsions such as better ductility and plasticity.
KEYWORDS: CRE Crumb Rubber Emulsions, modified emulsions, HIPE ( High Internal Phase
Emulsions, settlement, stability.
Page 2
Crumb rubber modified bituminous emulsions. CRE-EMULSIONS
1. Theoretical introduction
Bitumen emulsion is defined as a heterogeneous system comprising two or more
liquid phases, a continuous phase, water, and, at least, a second liquid phase, bitumen,
dispersed as droplets.
Bituminous emulsions are complex fluids. Its stability depends on the forces arising
from intermolecular attractive and repulsive forces that exist within the structure. Are
thermodynamically unstable systems; their instability is due to increased surface (∆A)
during emulsification, which produces an increase in the Gibbs free enthalpy (∆G):
where: γ = surface tension
Emulsions stability can be classified into: reversible or irreversible.
2. Reversible settling
2.1. Creaming and settling
Bitumen has a slightly higher density than water, therefore, due to the effect of
gravity drops tend to settle at the bottom of the container; that is when sedimentation
occurs. By adding a solvent to the bitumen, this can take less dense than water and
rise toward the surface, this phenomenon is known as creaming:
We can predict this rate of sedimentation through Stokes' law:
where, V= final speed; cm/s
r = particle radius; cm
δ globules - δ continuous phase = dispersed phase density and
dispersing phase
g= gravitational acceleration; 980 cm / s2
η= viscosity of dispersing phase; ( g/cm/s )
∆G = γ x ∆A
2g. r2 (δ globules - δ cont. phase
V = ────────────────────────
9 η
Page 3
Crumb rubber modified bituminous emulsions. CRE-EMULSIONS
3
If δ globules > δ continuous phase → V > 0 SETTLING
If δ globules < δ continuous phase → V < 0 CREAMING
Therefore, the average particle size of an emulsion is directly proportional to the
sedimentation velocity and inversely proportional to viscosity. Ie, the smaller particle
average is, the lower sedimentation rate and higher viscosity, to the same
concentration of residual binder.
In short, the settling speed can be reduced:
• Improving the storage conditions, keeping the emulsion at low temperatures
and / or stirring in short periods of time.
• Reducing the density of bitumen by adding a solvent.
• Preventing flocculation changing the type and concentration of surfactant or
by changing pH.
• Increasing the bitumen content.
• Increasing the emulsion viscosity.
• Decreasing the particle size of the bitumen globules
2.2 Flocculation
Flocculation is a process in which droplets begin to join each other. Normally
there is a larger central droplet surrounded by smaller droplets. Therefore, much more
homogeneous emulsion has less flocculation. Normally flocculation disappears with
stirring.
Flocculation speed decreases to reduce the concentration of the dispersed phase and a
lesser proportion as the temperature decreases as the kinetic energy of the globules
increases with increasing temperature.
3. Irreversible settling. Coalescence
When two droplets merge and form larger particles, the emulsion tends to break.
This effect begins with flocculation, but does not disappear with stirring. This effect
can come influenced by the content of emulsifier, a wrong choice of emulsifier,
erroneous use of temperatures during the production process or storing.
The coalescence rate depends on:
• The speed of flocculation prior to fusion of the droplets (hence, the
concentration of the dispersed phase).
• The properties of the interface (electrical charges, crystalline liquid
properties)
Page 4
Crumb rubber modified bituminous emulsions. CRE-EMULSIONS
• HLB (hydrophilic-lipophilic balance) of the emulsifier, chemical
composition and concentration.
4. Manufacturing of a bitumen emulsion with crumb rubber
In the previous section we have tried to emphasize the importance of particle size of
an emulsion in its final properties and size distribution, analytically called SPAM.
The particle size and distribution are controlled by the formulation, the
chemicals used, and especially with the manufacturing system.
In a conventional system, using high shear colloid mills, where, low viscosity bitumen
is used: 800 to 200 mPas at temperatures between 120-140 ° C, under turbulent
regime and a temperature for the acid continuous phase about 40-60 ° C. This
manufacturing system limits the final viscosity of the emulsion, the average size and
maximum particle concentration and the final bitumen emulsion.With conventional
manufacturing systems, limiting the average emulsion particle size to 5- 10 microns,
but maximum sizes up to 50 microns are commonly achieved.
To formulate this kind of new emulsions we have used a different kind of
manufacture. We have used a technique known as HIPE: High Internal Phase
Emulsion.
The HIPE process is based on the following items:
• The emulsions are manufactured in concentrated regime, in inversion
phase.
• It operates at high viscosity for the dispersed phase, around 1 Pa.s.
• The mixing speed is low, less than 1000 r. p.m.
• Once the emulsion is formed, we obtain a viscoelastic paste which is
diluted in water since the concentration desired.
• The emulsions are stored at required temperature.
The parameters that will influence the final characteristics of the emulsion are:
Dispersion energy
Dispersion in a emulsion is due to mechanical energy and applied physical
chemistry. The mechanical energy provided by the colloid mill divides the binder into
small particles, physicochemical energy is given by the emulsifier and should:
• Reduce the interfacial tension between the hydrocarbon phase (bitumen) and
the aqueous phase (water) to facilitate emulsification.
• Create a protective film around the particles.
•
Page 5
Crumb rubber modified bituminous emulsions. CRE-EMULSIONS
5
In other words, there must be sufficient mechanical energy to provide bitumen
particles of a size and correct concentration and sufficient surfactant to maintain the
stability of the emulsion.
Shear rate
In addition to the raw materials and formulation, particle size and distribution are
controlled by the shear rate.
The aim is to improve the formation and distribution of the droplets of bitumen.
Final sizes are controlled directly under the manufacturing method and can be
expressed as:
Shear Rate = 2πRV/ 60E
Where:
R = Dispersion mil radius (rotor and stator type);
V = Rotation speed (rpm);
E = gap
5. Emulsion design
Several formulations are made, with residual bitumen concentrations ranging
between 55 and 62% and rubber concentrations between 1-6%. For emulsification, a
diamine type surfactant is employed with a concentration between 0.4% -0.6%.
Selected crumb rubber presented a good digestion ability with bitumen, shows a very
fine granulometry with a particle size less than 400 microns and a low density such
that their dispersion into the bitumen has been very effective.
Results presented in this paper correspond only one type of formulation, which
showed the best results.
5.1 Physical characterization of CRE-emulsion through standard tests:
It makes a first physico-chemical characterization of the emulsion based on
conventional empirical tests for the specification of technical requirements. These
were compared with the results of an polymer-modified emulsion C60BP4 type very
common in road applications:
Page 6
Crumb rubber modified bituminous emulsions. CRE-EMULSIONS
PROPERTIES CRE-emulsión C60BP4
Test standard unit values
original emulsion
Residual binder NLT-139 % 60 59
Sieving NLT-142 % 0,30 0,04
Saybolt viscosity NLT-138 s 130 48
Settling NLT- 140 % 2 5
Evaporation residue to 163ºC ( NLT-147 )
Penetration
( 25ºC,100g,5s)
NLT-124 0,1mm 76 130
Softtening point R&B NLT-125 ºC 58 48
Table 1. Summary of the physico-chemical characterization of the initial emulsion.
CRE-emulsion has very high values of sieving, since not all the crumb rubber is
digested into the bitumen matrix and is retained in the 0.8 mm sieve. This is a very
viscous emulsion, with values of 130 s which almost triple those of a conventional
emulsion with same residual bitumen content.
An important parameter to be highlighted is their excellent settling value of just
2%, which means that the emulsion is very stable to storage. Finally, should be noted
that this is a modified emulsion with a bitumen residue tougher than his counterpart,
for the benefits they derive from the crumb rubber to bitumen.
Its elastic properties were also evaluated by testing force- ductility at 5ºC
( UNE-EN 13589) since it is a modified emulsion. Results are shown in the following
graph:
Draw 1. Plotting of force (N) vs strain (mm) according to force-ductility test at 5ºC.
0.00
5.00
10.00
15.00
20.00
25.00
0 50 100 150 200 250 300 350 400
Fo
rce
( N
)
Deformation ( mm )
FORCE-DUCTILITY
CRE-EMULSION 2
CRE-EMULSION 1
Page 7
Crumb rubber modified bituminous emulsions. CRE-EMULSIONS
7
According to UNE-EN 13589: Determination of tensile properties of modified
bitumen by the force-ductility method and the standard UNE-EN 13703:
Determination of the strain energy It can be reached to obtain a value for the
cohesion force ductility 5 ° C using the following formula:
Ei = ni x Eu
Where: Eu = du x Fu
D
du= ─────
V x t
D = specimen elongation
V= plotting speed
t= test time
Therefore,
E STRAIN CREEMULSION 1 CREEMULSION 2 C60BP4
J/cm2 0.406 0.563 ≥ 1
Table 2. Summary of strain energies for each sample of emulsion.
Energy values are below those required for a conventional C60BP4 emulsion
although the amount of crumb rubber contained in these samples was lower than the
equivalent quantity of polymer in a C60BP4 type emulsion.
5.2 Particle size determination
It was also determined the particle size of these emulsions to be an important
parameter as already discussed above.
For determining particle size, a laser diffraction technique was used. As can be seen in
the table below, the particle size average of this emulsion is about 4 microns, and its
maximum size is only 8 microns.
These results agree with the excellent sedimentation values presented above, since
according to Stokes law, the lower the average particle size, the lower settling rate is.
Page 8
Crumb rubber modified bituminous emulsions. CRE-EMULSIONS
Particle size T min (d0,1) T average (d0,5) T max. (d0,9)
µm 1,980 4,004 7,982
Figure 1: Particle size distribution of a bituminous emulsion with crumb rubber
5.3 Settling evaluation
Finally, special attention is devoted to the study of SETTLING, being a feature
hard to be solved in bituminous binders containing crumb rubber in their formulation.
In this case two methods were developed:
5.3.1 STANDARD TEST NLT-140 :
Figure 2. Test device for determination of settling in bitumen emulsions
In this case, as already mentioned above, values of settling around 2% are
obtained, which suggests that formulation of these crumb rubber emulsions is suitable,
and allows obtaining crumb rubber modified emulsion very stable over time.
Particle Size Distribution
0.1 1 10 100 1000
Particle Size (µm)
0
2
4
6
8
10
Percentage of
settled bitumen =
Top A
Bottom B
Page 9
Crumb rubber modified bituminous emulsions. CRE-EMULSIONS
9
5.3.2 Setting A: qualitative and quantitative study
In order to analyze the dispersion of the rubber powder within the emulsion and
to check the tendency to sedimentation of the CRE-emulsion using two tubes type
"toothpaste" were used to evaluate the stability of modified polymer bitumens. In each
150 milliliters of emulsion are poured and left for seven days at room temperature, as
if it were the classic sedimentation test. After this period of rest, the two tubes are
placed in a freezer at -20 ° C for 24 hours. One of the two tubes is cut in two halves
in order to visually evaluate the dispersion of the rubber while the latter is cut into
three parts.
To determine the degree of homogeneity of the binder water is firstly removed by
evaporation at a temperature of 50 ° C until constant weight. After completion of the
evaporation of water, residual binder modified with crumb rubber is extracted with
tetrahydrofuran, with a proportion of 50 milliliters per 1 gram of residual bitumen,
and determining the percentage of crumb rubber in each.
As stated earlier, after letting stand the emulsion for seven days at room temperature
and placed in a freezer at -20 ° C, the distribution of crumb rubber is evaluated in
two ways:
Qualitative study
This is a visual inspection of crumb rubber distribution within the bitumen. To
this end, the tube of teeth in two halves shows the distribution of rubber
Top of the test tube
Figure 3: Visual assessment of dispersion of rubber within the emulsion
Page 10
Crumb rubber modified bituminous emulsions. CRE-EMULSIONS
Quantitative test
In this case, the tube is cut into three slices in order to determine after complete
evaporation of water and extraction with tetrahydrofuran, the amount of crumb rubber
contained in each slice.
TOP MIDDLE BOTTOM
Figure 4: Test method of the dispersion of crumb rubber within the emulsion
Crumb rubber contents for each section of the test tube are as follows:
Tube sections Crumb rubber content (%)
Top 3,6%
Middle 3,5%
Bottom 4,2%
Table 3: Summary of crumb rubber contents through THF testing.
As can be seen, the distribution of crumb rubber is fairly uniform. These three
values are very similar and show a perfect distribution of crumb rubber in the
volume of the emulsion thus supporting the preceding visual assessment and the
excellent stability determined by the sedimentation testing of the crumb rubber-
emulsion.
6. Residual binder rheological characterization of the crumb rubber-
emulsion:
Bitumens are viscoelastic materials, ie, when subjected to a stress, the material
response is translated into two components: an elastic, when the stress is removed
recovers the initial position, and a viscous, where the deformation is permanent. This
behavior is a function of temperature and load. Thus, to properly characterize bitumen
must be at least two of its properties: the material's resistance to deformation and its
distribution between elastic and viscous components. The experimental form of this
behavior is measured by dynamic oscillation tests that use a dynamic shear rheometer
(DSR) following the procedure described in standard EN 14770 - Determination of
complex modulus and phase angle by a dynamic shear rheometer. This device allows
Page 11
Crumb rubber modified bituminous emulsions. CRE-EMULSIONS
11
to evaluate the viscoelastic behavior of the binder through the measurement of
complex modulus G *, indicator of the relationship between the applied stress and
strain, phase angle, δ, refered to the recoverable and non-recoverable deformation, for
the three critical conditions of the binder.
To study the behavior of the binder three critical areas of temperature and try can
be studied to correlate them with the final properties of the binder:
• T> 100 ° C bitumen behave as Newtonian fluids. Measuring the viscosity is
sufficient to evaluate its workability. It is independent of applied stress.
• 45> T <85 ° C: Pavement deterioration is caused mostly by plastic
deformation. It is necessary to measure G * and δ to know their behavior.
The higher G *, the higher the resistance to deformation, therefore, less
failure by plastic deformation, and the smaller δ, the more elastic behavior
of the binder thus less plastic deformation fault. This deterioration is a
function of the applied load, therefore, should be considered to study fast
loading cycles, resulting in measurements at 10 rad / s, which are equivalent
to speeds of 75-90 km / h.
• 0> T <45 ° C: In this case, failure in the pavement is caused mostly by
fatigue caused by repeated loading cycles. At these temperatures bitumen is
harder and less elastic. Again we measure G * and δ, then the damage will
depend on how much strain occurs and how much of this strain is
recoverable. The results will be also a function of loading time, so we must
perform the tests at 10 rad / s, ie 1.59 Hz
In addition to the SUPERPAVE criteria, used to evaluate the behavior of different
binders to plastic deformation and fatigue, a frequency sweep of the samples between
0.01 and 10 Hz was performed, at two test temperatures: 25 ° C and 58 ° C, to study
the variation of module vs frequency.
Residual bitumen of crumb rubber modified mulsion was analyzed and
compared with the residue of an emulsion binder modified with polymers. As a
reference are also show the results of crumb rubber modified bitumen type (BMC-
3b) and a polymer modified bitumen (BM-3b), which should show the most elastic
behavior.
All binders have been characterized in its original condition. The results
obtained are represented by the diagram of Black, variation of the complex modulus,
G *, with the variation of phase angle, δ, and variation of modulus as a function of
frequency.
Page 12
Crumb rubber modified bituminous emulsions. CRE-EMULSIONS
In the Black diagram can be seen two distinct behaviors: a linear behavior, due
to the low elastic contribution, and an S-shaped behavior, characteristic of binders
containing polymers, due to the interaction of the elastic behavior of polymer and
viscoelastic behavior of the modified binder. The following plot shows the behavior of
these four binders:
Figure 4: Black Diagram for each of the four binders.
It is observed that the binder which has greater elastic behavior, S-curve, is the
corresponding to polymer-modified bitumen, represented in green color, followed by
the bitumen modified with crumb rubber, in blue, and the residue of the polymer-
modified emulsion, brown colored. Finally, the binder with a lower elastic behavior is
the corresponding residue of the emulsion with crumb rubber as the rubber amount
incorporated is still too small for this property can be significant.
Besides, it can be seen clearly the difference in viscoelastic behavior between
different binders. At high temperatures, the binder having higher values of G *, ie
greater resistance to strain, is the corresponding to polymer modified bitumen, but it
should be noted that the value of residual bitumen-emulsion with crumb rubber is
practically the same. Whereas at intermediate temperatures, the smaller value of δ, the
more elastic behavior, which corresponds to crumb rubber modified bitumen,
followed by the residue of crumb rubber emulsion, that would display the same value
as the residue of polymer modified emulsion.
Graph below illustrates the modules G '(elastic contribution) and G'' (viscous
contribution) at intermediate temperature, 25 ° C throughout the frequency range for
Black Diagram
1,00E+01
1,00E+02
1,00E+04
1,00E+05
1,00E+06
1,00E+07
30 40 50 60 70 80 90 100
δ
G*
1,00E+03
Tª intermediate: 25ºC
Tª high : 58ºC
■ Crumb rubber residue
■ Polymer modified residue
■ BM3b
■ BMC-3b
Page 13
Crumb rubber modified bituminous emulsions. CRE-EMULSIONS
13
the residue of the crumb rubber emulsion and the residue of an emulsion modified
with polymers. These two residues show mainly viscous behavior, since values of G''
are found throughout the frequency range above the values of G '. For long loading,
0.01Hz frequency, the residue of the crumb rubber gives lower values, ie, worse
fatigue behavior, although for rapid loading, frequencies of 10 Hz, both binders have
similar behaviors.
Figure 5: Viscous and elastic modulo as a function of frequency of a residue of an
polymer modified emulsion and a residue from the crumb rubber-emulsion at 25 ° C
.
7. Conclusions:
• A new generation of modified emulsions made with crumb rubber from used
tires, stable to storage, has been developed.
Initial physicochemical characterization tests allow us to evaluate the
characteristics of this binder comparable with a commercial polymer-modified
emulsion. It is worth noting the excellent values obtained in the settling test,
NLT-140.
• Force ductility test,UNE-EN 13589, shows that it is an emulsion with a high
cohesion value when considering that the amount of crumb rubber contained in
it is far below the amount of polymer used to manufacture commercial modified
emulsion.
Qualitative evaluation joined to quantitative tests with THF confirms the
excellent values obtained in the settling test.
Modulus as a function of frequency at 25ºC
1,00E+03
1,00E+04
1,00E+05
1,00E+06
1,00E+07
0, 01 0, 1 1 1Frequency (Hz)
FAST SPEED
SLOW SPEED
■ G’ crumb rubber emulsion residue
■ G’’ crumb rubber emulsion residue
■ G’ polymer modified emulsion residue
■ G’’ polymer modified emulsion residue
Modulus (Pa)
Page 14
Crumb rubber modified bituminous emulsions. CRE-EMULSIONS
• Under the Black diagram, the elastic behavior of the crumb rubber-emulsion is
not significant compared with a reference C60BP4 emulsion, but the maximum
amount of crumb rubber that can be incorporated in these emulsions is yet to
be determined and this property may vary significantly. For high temperatures,
58 ° C, the value of G * for the residue of crumb rubber emulsion is almost
similar to the polymer modified emulsion. For intermediate temperatures, 25 °
C, the value of δ is equal for both binders mentioned above.
• In the frequency sweep, for slow loading, the residue of the polymer modified
emulsion provides better results, but for rapid loading, G'' values are similar for
both binders.
By tuning the formulation of the latest generation of emulsion modified with
crumb rubber, it is possible to managed to combine the advantages of use of
emulsions in road construction to the advantages provided by the crumb rubber
modified binder with an very important environmental commitment to work with this
new binder in reuse, recycling and disposal of this waste.
Page 15
Crumb rubber modified bituminous emulsions. CRE-EMULSIONS
15
9. Bibliography
[1] Dupon. Invention et évolution des pneumatiques, www.moto-histo.com/pneus/pneus.htm,
2009
[2] CEDEX..Ministerio de Medio Ambiente: Manual de empleo de caucho de NFU en
mezclas bituminosas 2007
[3] Samaraez Chemical Consulting: Reciclaje de neumáticos fuera de uso – Trituración
mecánica. 2008.
[4] POTTI, Juan Jose Innovaciones en ligantes bituminosos, Revista CARRETERAS, núm.
138, 2005
[5] COLAS VICTORIA Ma Mar, et al.. Reología de los betunes con caucho, VIII Congreso
Nacional de firmes. 2008
[6] UNE-EN 1429. Determinación del residuo por tamizado de las emulsiones bituminosas, y
determinación de la estabilidad al almacenamiento por tamizado, 2009
[7] NLT – 138. Viscosidad Saybolt de las emulsiones bituminosas, 1999
[8] NLT – 140 Sedimentación de las emulsiones bituminosas, UNE-EN 12847: Determinación
de la tendencia a la sedimentación de las emulsiones bituminosas, 2009.
[9] ISO 13320: Particle size analysis – Laser diffraction methods, 2009
[10] Potti, JJ.. “Emulsiones catiónicas de rotura lenta en carreteras. Primeros resultados del
proyecto Europeo Optel”. Revista “Carreteras” número 103 páginas 81- 97. 1999
[11] K. Van Nieuwenhuyze, et al.”Understanding the relationship between emulsion properties
and binder/emulsifier characteristics.” European Research project. Cold Mix Technology.
Revue Générale des Routes et des Aérodromes numéro 793. 2001.
[12] L. Bonakdar, J. et al. “Rupturing of bitumen-in-water emulsions: experimental evidence for
viscous sintering phenomena.” Paper accepted for publication in Colloids and Surfaces, A:
Physicochemical and Engineering Aspects 176. P.185-194. 2001
[13] Y. Lendresse, et al. “The performance of emulsion-grade bitumens. The use of a new
method for characterising their interfacial properties, Eurasphalt & Eurobitume Congress,
Strasbourg (France),, Paper nº 6.038. 1996