New Crumb rubber modified bituminous emulsions. CRE-emulsions · 2015. 12. 4. · bitumen by the force-ductility method and the standard UNE-EN 13703: ... For determining particle

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.

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


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)


• 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.

•


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:


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


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.


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


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


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


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.


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


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)


• 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.


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

Documents

New Crumb rubber modified bituminous emulsions. CRE-emulsions · 2015. 12. 4. · bitumen by the force-ductility method and the standard UNE-EN 13703: ... For determining particle