Fuels & Lubricants Magazine

Because of the development of
road transportation and the constant
quality problems of roads, in some
less developed countries, new and
economical solutions are needed in
road constructions. For a century,
bitumen has been successfully used
in asphalt, concrete to construct
roads. Despite the improvements of
bitumen production, road construction
and design, there are limits to
meet new challenges. Growing traffic,
increasing loads of heavy trucks,
extreme climates and construction
shortcomings are taking a toll.
Additionally, there is an increasing
demand for safer, quieter highways
and roads. Polymer modification
(e.g. styrene-butadiene-styrene or
SBS) of bitumen can help to overcome
these challenges. However, the
application of the special bitumen
additives is expensive (12, 13).
The production of rubber bitumen
by blending of bitumen with
used tyres based crumb rubber is not
just a waste handling method, but
an excellent and economic solution
to upgrade the quality of the heavy
residue, improving the performance
of asphalt pavements compared to
roads made of conventional bitumen.
The technology was applied
first in the US in the sixties. The
following advantages are usually
highlighted in case of rubber bitumen
application (12-14):
• longer life time,
• lower life cycle cost,
• better low temperature performance,
• wider utilization temperature
range,
• less deformation,
• better fatigue characteristics,
• better adhesion to aggregates results,
thus improved durability,
• noise reduction effect.
However, many existing technologies
and rubber bitumen products
have some drawbacks (12-15):
• altering product quality,
• quick phase separation (transportation
and storage problems),
• high viscosity (pumping problems),
• spraying problems,
• necessity of special equipment
(investment required),
• special asphalt mixture is required,
• compatibility problems,
• emission of harmful gases.
Therefore University of Pannonia
and MOL Plc. developed a
new, patented production method
(WO/2007/068990, HU226481),
which is capable to produce chemically
stabilized rubber bitumen in a
crude oil refinery according to the
best available technique. The target
was to keep the advantageous properties
and minimise the disadvantages
of rubber bitumen product.
Results and discussion
As it was presented in our earlier
publications (14, 15) several rubber
modified bitumen (RmB) production
test runs were organised by the
research team of University of Pannonia
and MOL before 2012 in Zala
Refinery (Hungary) after temporary
modification of an existing polymer
modification bitumen (PmB) plant.
Test runs with regard to the following
asphalt laboratory assessments,
asphalt mixture productions and test
road constructions were very promising.
The quality and durability of
constructed asphalt roads together
Figure 1: Upgrading
options of heavy
residues producing
lighter fractions
with the gained experiences stimulated
the construction of a new rubber
bitumen unit. As a result MOL
revamped an existing PmB plant. In
the unit both PmB and chemically
stabilised RmB with the improved
wet process can be produced. The
nominal capacity of the prototype
RmB unit is 5 kt/year.
The patented process, consists
of two technological steps. In the
first one, chemical degradation of
crumb rubber occurs at high temperature.
The second step involves
a high shear mixing with the application
of colloid mill. It occurs at
moderate temperature and supports
re-vulcanization of dissolved parts
of crumb rubber in bitumen. During
the production a multifunctional
additive (produced by MOL) is applied
as well, which promotes rubber
dissolution and decreases separation
ability of undissolved rubber particles.
At the same time, the applied
additive decreases the viscosity of
the product providing better processability
in asphalt mixing and
pavement construction.
The insoluble particles in the final
RmB product are below 50% calculated
on the initially added crumb
rubber. It means that more than half
of used rubber completely dissolves
and behaves as active modifying
agent similarly to SBS used for
polymer modified bitumen production.
The swelled but not completely
dissolved particles contribute to
20 Fuels&Lubricants No. 1 OCTOBER 2017