Storage Stable Crumb Rubber Modified Bitumen & Method of
Manufacturing thereof
Field of Invention
The present invention is directed to improve the stiffness, elastic recovery and storage stability of bitumen to desired level by mixing crumb rubber powder particle size less than 3mm preferably less than 600 micron, natural asphalt / gilsonite in presence of poly-phosphoric acid. The present invention is also directed to the method of manufacturing crumb rubber modified bitumen using crumb rubber powder, natural asphalt and poly-phosphoric acid. The present invention claims that the crumb rubber modified bitumen produced using crumb rubber powder, natural asphalt / Gilsonite and poly-phosphoric acid exhibits improvement in stiffness (viscosity), softening point, elastic recovery and in the storage stability to desired level from the base bitumen. The laboratory test data of crumb rubber modified bitumen exhibits better rutting resistance (G* / sin8), intermittent and low temperature cracking resistance in comparison to base bitumen.
Background
As used herein, the phrase "Bitumen" refers to refinery product used to pave the roads after mixing with aggregates. Similarly as used herein, the phrase " Crumb Rubber powder " refers to ground tire rubber / particle size less than 3mm preferably less than 600 micron. The crumb rubber, less than 2mm size has been used for modifying the properties of bitumen either alone or along with poly-phosphoric acid, publication number WO 04 / 081098 or in combination of cross linking agent and / or with additional synthetic polymer, publication number PCT / US 2006/016966.
Bitumen 80/100 & 60/70 grades are normally used for pavement construction in India depending on climatic environmental conditions. Bitumen is a thermoplastic material and at higher temperature becomes soft / less stiffen Therefore, in summer under high axel load and traffic density the pavements suffer with rutting. Similarly at low temperature the bitumen gets brittle leading to pavement cracking due to thermal stress. Therefore, the bitumen is normally modified with natural rubber (latex), crumb rubber powder and synthetic polymers. The modified bitumen exhibits better resistance to rutting, fatigue cracking, elastic recovery and adhesion with aggregates in comparison to neat bitumen. To improve the service life of pavement, sometimes an anti-stripping agent is mixed either in bitumen or with aggregate.
To improve the elastic recovery of bitumen, crumb rubber powder, particle size less than 2 mm or synthetic polymers are mixed with bitumen. It has also been noticed that the mixing of crumb rubber powder increases the stiffness of the bitumen, but it may leads to bitumen-storage problem due to the separation of dispersed crumb rubber from the bitumen, if mixed in higher concentrations. The objective of this invention is to produce the Storage-Stable Crumb Rubber Modified Bitumen with required stiffness (viscosity), elastic recovery having better rutting resistance and cracking resistance at intermitant and low temperatures without using expensive synthetic polymers.
SUMMARY OF INVENTION
In one aspect, the present invention is directed to a crumb rubber modified bitumen comprising of bitumen, crumb rubber powder, natural asphalt / gilsonite and poly-phosphoric acid without adding any additional synthetic polymer. In one embodiment the neat bitumen was modified by mixing 0.5 to 20% by weight of crumb rubber, 0.2 to 10% by weight of natural asphalt / gilsonite and 0.2 to 5 % by weight of poly-phosphoric acid. The elastic recovery of crumb rubber modified bitumen was improved to 66% from 17% of neat bitumen on bitumen modification.

In Another aspect the present invention is directed to manufacturing method of crumb rubber modified bitumen that comprises of bitumen, crumb rubber powder, natural asphalt & poly-phosphoric acid. In the present invention, prepared crumb rubber modified bitumen has elastic recovery typically between 35 to 70 % that was measured following a test method described in Annexure-A of 13:15462-2004. The Storage-Stability-lndex value of the prepared crumb rubber modified bitumen has value typically between 0.3 to 2.0. The storage stability index value was measured by following a modified-test protocol described in Annexure-B of IS-15462: 2004. In this test protocol the bitumen (50 g) is taken in blind aluminum tube of diameter 25.4 mm and length of 136.7 mm. The tube is sealed and kept in air oven at 163+5 °C for 48 hrs in vertical position. After storage of bitumen for 48 hrs at 163 °C, the aluminum tube is kept in refrigerator at 6.71 °C for 4hrs in vertical position so the bitumen gets solidify. There after, the tube is cut in to three equal length-sections and bitumen from top and bottom sections are removed. The bitumen, removed from top and bottom sections, are tested for softening point following standard 13:1205-1987 test protocol. The difference in softening point values of bitumen, obtained from top & bottom sections / layers, is called storage stability index of bitumen. Low value of storage stability index is an indicative of homogeneity of the product (modified bitumen) due to the uniform distribution of modifiers / modifying agent in the top to bottom layers of bitumen. Generally, the modified bitumen with storage stability index value up to 4 units is acceptable. The Storage-Stability-Index value indicates that how stable is the modified bitumen during storage. The modified bitumen with larger values of storage stability index (more than 4) considered storage unstable and requires agitation during transportation & storage to maintain the homogeneity of the product.
Description of preferred Embodiments
1. The present invention is directed to crumb rubber-modified bitumen and method of manufacturing of crumb rubber modified bitumen of desired properties.
The crumb rubber modified bitumen comprise of neat bitumen, crumb rubber powder, natural asphalt or gilsonite and poly-phosphoric acid with out using any addition synthetic polymers. The crumb rubber powder, used in the study, is a ground tire rubber in the form of power having particle size less than 3mm and preferably less than 600 micron size. The invention is not limited with the particle size of crumb rubber; it may have any particle size distribution that result the crumb rubber modified bitumen with desired properties.
1. In the present invention the crumb rubber modified bitumen comprises of
between 65 to 96% of bitumen by weight, between 0.5 to 20 % crumb
rubber by weight, between 0.2 to 5% of poly-phosphoric acid by weight
and between 0.2 to 10% of natural asphalt / gilsonite by weight.
2. In a preferred embodiment of crumb rubber modified bitumen is comprises
about between 82 to 95%of bitumen by weight, between 1.0 to 10 % of
crumb rubber by weight, particle size less than 600 micron, between 0.5 to
5% of natural asphalt / gilsonite by weight and between 0.5 to 3% poly-
phosphoric acid by weight.
3. In a particularly preferred embodiment, the modified bitumen comprised of
between 85 to 94%of bitumen, between 1.0 to 8 % of crumb rubber,
particle size less than 600 micron, between 0.5 to 5% of natural asphalt /
gilsonite by weight and between 0.5 to 2.0% poly-phosphoric acid by
weight.
4. In the present invention, the preferred natural asphalt / gilsonite for used
having the particle size less than 5mm and ash content less than 2% by
weight. The invention is not limited in this respect and any material
suitable to increase the stiffness and softening point of bitumen known to
those skilled in the art may be used in the modification of bitumen.
5. In the present invention, the poly phosphoric acid having ortho phosphoric
content more than 110 % either may be in liquid or may be in semisolid /
solid form at room temperature may be used.
6. The second aspect of the present invention is the method of
manufacturing the crumb rubber modified bitumen. The method of
producing the crumb rubber modified bitumen comprises of the following
steps.
6.1 Heating the bitumen between 135 to 190 degree Celsius in suitable
container equipped with suitable stirring and re-circulation arrangement
or bitumen modification pilot plant.
6.2 Adding the first modifying ingredient to hot bitumen.

6.3 Mixing the first modifying ingredient with hot bitumen in bitumen-
modification-plant by maintaining the speed of stirrer in such a way so
mixture forming vortex cutting angle about 40° for a period between 15
minutes to 10 hrs.
6.4 Adding the second modifying ingredient to hot modified bitumen.

6.5 Mixing the second modifying ingredient with hot modified bitumen in
bitumen-modification-plant by maintaining the speed of stirrer in such a
way so mixture forming vortex cutting angle about 40° for a period
between 15 minutes to 10 hrs.
6.6 Adding the third modifying ingredient to hot modified bitumen.
6.7 Mixing the third modifying ingredient with hot modified bitumen in
bitumen-modification-plant by maintaining the speed of stirrer in such a
way so mixture forming vortex cutting angle about 40° for a period
between 15 minutes to 10 hrs.
7. The modifying ingredient are crumb rubber powder, natural asphalt /
gilsonite and poly-phosphoric acid may be added and mixed with hot
bitumen in any sequence i.e. the first modifying agent may be crumb rubber powder, second may be natural asphalt / gilsonite and third may be poly-phosphoric acid or first modifying agent may be natural asphalt / gilsonite, second may be crumb rubber powder and third one may be poly-phosphoric acid. Alternatively the first modifying agent may be crumb rubber powder, second may be poly-phosphoric acid and third may be natural asphalt/ gilsonite or first may be natural asphalt / gilsonite, second may be poly phosphoric acid and third may be crumb rubber powder. Similarly the first modifying ingredient may be poly-phosphoric acid, second crumb rubber powder and third natural asphalt / gilsonite or the first poly phosphoric acid, second natural asphalt/ gilsonite and third crumb rubber powder.
8. The mixing time of ingredient depends on the temperature of bitumen and
speed and type of stirrer (high shear and low shear), and mixing time may
be altered and optimized by those who are skilled in the art. In a preferred
embodiment, the bitumen was mixed/ stirred for 2-3 hrs after adding of
crumb rubber powder, 15 minutes to 1 hr after adding natural asphalt /
gilsonite and 30 minutes to 2 hrs after adding poly phosphoric acid.
9. In the present invention, manufacturing-method of crumb rubber modified
bitumen, the crumb rubber powder between 0.5 to 20 % by weight, poly-
phosphoric acid between 0.2 to 5% by weight and natural asphalt /
gilsonite between 0.2 to 10% by weight of modified bitumen were used.
10. In the present invention the methods for manufacturing of crumb rubber
modified bitumen have been presented below:
Example-1
10.1.1 Neat bitumen is heated between 135 to 190 °C in Bitumen
modification Pilot Plant (ENH, Germany Make).
10.1.2 Crumb rubber powder, particle size less than 3mm, between
0.5 to 20 % by weight was added to bitumen.
10.1.3 Mixture was stirred between 15 minutes to 10 hrs with
appropriate speed of stirrer forming vortex-cutting angle about
40°.
10.1.4 Natural asphalt / Gilsonite was added between 0.2 to 10% by
weight.
10.1.5 Mixture was stirred between 15minutes to 10 hrs with
appropriate speed of stirrer forming vortex-cutting angle about
40°.
10.1.6 Poly-phosphoric acid was added between 0.2 to 5% by weight.
10.1.7 Mixture was stirred between 15 minutes to 10 hrs with
appropriate speed of stirrer forming vortex-cutting angle about
40°.
Example-2
10.2.1 Neat bitumen is heated between 139 to 190 °C in Bitumen
Modification Pilot Plant (ENH, Germany Make).
10.2.2 Natural asphalt / Gilsonite was added between 0.2 to 10% by
weight.
10.2.3 Mixture was stirred between 15 minutes to 10 hrs with
appropriate speed of stirrer forming vortex-cutting angle about
40°.
10.2.4 Crumb rubber powder, particle size less than 3mm, between
0.5to 20% by weight was added to bitumen.
10.2.5 Mixture was stirred between 15 minutes to 10 hrs with
appropriate speed of stirrer forming vortex-cutting angle about
40°.
10.2.6 Poly-phosphoric acid was added between 0.2 to 5 % by weight.
10.2.7 Mixture was stirred between 15 minutes to 10 hrs with
appropriate speed of stirrer forming vortex-cutting angle about
40°.
Example-3
10.3.1 Neat bitumen is heated between 135 to 190°C in bitumen
modification Pilot Plant (ENH, Germany Make).
10.3.2 Crumb rubber powder, particle size less than 3mm, between 0.5
to 20% by weight was added to bitumen.
10.3.3 Mixture was stirred between 15 minutes to 10 hrs with
appropriate speed of stirrer forming vortex-cutting angle about
40°.
10.3.4 Poly-phosphoric acid was added between 0.2 to 5 % by weight.
10.3.5 Mixture was stirred between 15 minutes to 10 hrs with
appropriate speed of stirrer forming vortex-cutting angle about
40°.
10.3.6 Natural asphalt / Gilsonite was added between 0.2 to 10% by
weight.
10.3.7 Mixture was stirred between 15 minutes to 10 hrs with
appropriate speed of stirrer forming vortex-cutting angle about
40°.
Example-4
10.4.1 Neat bitumen is heated between 135 to 190°C in bitumen
modification Pilot Plant (ENH, Germany Make).
10.4.2 Natural asphalt / Gilsonite was added between 0.2 to 10% by
weight.
10.4.3 Mixture was stirred between 15 minutes to 10 hrs with
appropriate speed of stirrer forming vortex-cutting angle about
40°.
10.4.4 Poly-phosphoric acid was added between 0.2 to 5 % by weight.
10.4.5 Mixture was stirred between 15 minutes to 10 hrs with
appropriate speed of stirrer forming vortex-cutting angle about
40°.
10.4.6 Crumb rubber powder, particle size less than 3mm, between 0.5
to 20% was added to bitumen.
10.4.7 Mixture was stirred between 15 minutes to 10 hrs with
appropriate speed of stirrer forming vortex-cutting angle about
40°.
Example-5
10.5.1 Neat bitumen is heated between 135 to 190°C in bitumen
modification Pilot Plant (ENH, Germany Make).
10.5.2 Poly-phosphoric acid was added between 0.2 to 5 % by weight.
10.5.3 Mixture was stirred between 15 minutes to 10 hrs with
appropriate speed of stirrer forming vortex-cutting angle about
40°.
10.5.4 Crumb rubber powder, particle size less than 3mm, between 0.5
to 20% was added to bitumen.
10.5.5 Mixture was stirred between 15 minutes to 10 hrs with
appropriate speed of stirrer forming vortex-cutting angle about
40°.
10.5.6 Natural asphalt / Gilsonite was added between 0.2 to 10% by
weight.
10.5.7 Mixture was stirred between 15minutes to 10 hrs with
appropriate speed of stirrer forming vortex-cutting angle about
40°.
Example- 6
10.6.1 Neat bitumen is heated between 135 to 190°C in bitumen
modification Pilot Plant (ENH, Germany Make).
10.6.2 Poly-phosphoric acid was added between 0.2 to 5 % by weight.
10.6.3 Mixture was stirred between 15 minutes to 10 hrs with
appropriate speed of stirrer forming vortex-cutting angle about
40°.
10.6.4 Natural asphalt / Gilsonite was added between 0.2 to 10% by
weight.
10.6.5 Mixture was stirred between 15 minutes to 10 hrs with
appropriate speed of stirrer forming vortex-cutting angle about
40°.
10.6.6 Crumb rubber powder, particle size less than 3mm, between 0.5
to 20% was added to bitumen.
10.6.7 Mixture was stirred between 15 minutes to 10 hrs with
appropriate speed of stirrer forming vortex-cutting angle about
40°.
In the present invention, the experimental conditions and the typical data of crumb rubber modified bitumen of following six experiments have been shown in Tables 1-6. The bitumen modification experiments were conducted in M/S ENH, Germany make, bitumen modification pilot plant equipped with desired stirring temperature, stirring speed, and bitumen re-circulation facilities. During the bitumen modification the stirring temperature was kept 165±2 °C in all the experiments. The ingredients were added in different sequences and the stirring time was kept 2 hrs after each addition of crumb rubber powder, 1 hr after each addition of natural asphalt / gilsonite and 1 hr after each addition of poly-phosphoric acid during the bitumen modification. The property of neat bitumen use for bitumen modification has been shown in table-7.
Table-1 Bitumen Modification with sequence of Bitumen-CR-GIL-PPA

(Table Removed)
Table-2 Bitumen Modification with sequence of Bitumen-GIL-CR-PPA

(Table Removed)
Table-3 Bitumen Modification with sequence of Bitumen-CR-PPA-GIL

(Table Removed)
Table-4 Bitumen Modification with sequence of Bitumen-GIL-PPA-CR

(Table Removed)
Table-5: Bitumen Modification with sequence of Bitumen- PPA-CR-GIL

(Table Removed)
Table-6: Bitumen Modification with sequence of Bitumen- PPA-GIL-CR
(Table Removed)
Table-7 Properties of Neat Bitumen, used for bitumen modification

(Table Removed)

We Claim:
1. Storage stable crumb rubber modified bitumen composition comprising :
65 - 95 wt% of bitumen, 0.5 - 20wt% of crumb rubber powder, 0.2 - 10 wt % of natural asphalt/gilsonite and 0.2 to 5 wt % of poly-phosphoric acid.
2. A composition as claimed in claim 1, wherein the said crumb rubber powder
has a particle size less than 3 mm.
3. A composition as claimed in claim 1, wherein the said natural asphalt /
gilsonite powder has a particle size less than 5 mm and ash content less than
5%.
4. A composition as claimed in claim 1, wherein the said poly phosphoric acid
has more than 110 % of ortho-phosphoric acid content.
5. A method of making crumb rubber modified bitumen composition as claimed
in claim 1 comprising the steps:
a) heating of bitumen to 135 to 190°C in a suitable container equipped with
suitable stirring and re-circulation arrangement or in bitumen modification
pilot plant to obtain hot bitumen; (b) adding each of 0.5 - 20wt% of crumb rubber powder, 0.2 - 10 wt %
of natural asphalt/gilsonite and 0.2 to 5 wt % of poly-phosphoric acid in any sequence to said hot bitumen followed by mixing after each addition for a period between 15 minutes to 10 hrs.
6. A method as claimed in claim 5, wherein the said mixing in step (b) is carried
out by maintaining the speed of stirrer in such a way so that mixture forms a
vortex cutting angle of about 40°'
7. A method as claimed in claim 5, wherein the said any sequence of addition in
step(b) comprises addition of crumb rubber powder followed by the addition of
natural asphalt / gilsonite and poly-phosphoric acid respectively in the said
concentrations.
8. A method as claimed in claim 5, wherein the said any sequence of addition in
step (b) comprises addition of natural asphalt / gilsonite followed by the addition
of crumb rubber powder and poly-phosphoric acid respectively in the said
concentrations.
9. A method as claimed in claim 5, wherein the said any sequence of addition in
step(b) comprises addition of crumb rubber powder followed by the addition of
poly-phosphoric acid and natural asphalt / gilsonite respectively in the said
concentrations.
10. A method as claimed in claim 5, wherein the said any sequence of addition in
step(b) comprises addition of natural asphalt / gilsonite followed by the addition
of poly-phosphoric acid and crumb rubber powder respectively in the said
concentrations.
11. A method as claimed in claim 5, wherein the said any sequence of addition
in step(b) comprises addition of poly-phosphoric acid followed by the addition of
crumb rubber powder and natural asphalt / gilsonite respectively in the said
concentrations.
12. A method as claimed in claim 5, wherein the said any sequence of addition
in step(b) comprises addition of poly-phosphoric acid followed by the addition of
natural asphalt / gilsonite and crumb rubber powder respectively in the said
concentrations .
13. Storage stable crumb rubber modified bitumen composition substantially as
herein described with references to the foregoing description, examples and
tables.
14. A method for making crumb rubber modified bitumen composition substantially as herein described with references to the foregoing description, examples and tables.