U.S. patent application number 09/868346 was filed with the patent office on 2002-11-21 for process and system for production of a warm foam mix asphalt composition.
Invention is credited to Larsen, Olle R., Robertus, Carl C..
Application Number | 20020170464 09/868346 |
Document ID | / |
Family ID | 19910789 |
Filed Date | 2002-11-21 |
United States Patent
Application |
20020170464 |
Kind Code |
A1 |
Larsen, Olle R. ; et
al. |
November 21, 2002 |
Process and system for production of a warm foam mix asphalt
composition
Abstract
The invention describes a process for preparing a warm mix
asphalt composition by mixing an aggregate grain material with a
soft binder, and adding a hard binder to the mixed aggregate grain
material. The hard binder is foamed in a foaming process before it
is introduced to the mixed grained aggregate material. A system for
preparing the warm mix asphalt composition comprising a drying drum
for heating and drying the aggregate component, a mixing mill for
mixing the asphalt components and a mix storage silo, where the
system also includes foam production facilities for foaming the
hard binder before introduction to the mixing mill, is also
disclosed.
Inventors: |
Larsen, Olle R.; (Anna
Hagmannsgate, NO) ; Robertus, Carl C.; (London,
GB) |
Correspondence
Address: |
LADAS & PARRY
26 WEST 61ST STREET
NEW YORK
NY
10023
US
|
Family ID: |
19910789 |
Appl. No.: |
09/868346 |
Filed: |
December 20, 2001 |
PCT Filed: |
February 5, 2001 |
PCT NO: |
PCT/NO01/00039 |
Current U.S.
Class: |
106/273.1 |
Current CPC
Class: |
E01C 7/18 20130101; E01C
19/1077 20130101; Y02A 30/30 20180101; C08L 95/00 20130101; C08L
93/00 20130101; C08L 93/00 20130101; C08L 95/00 20130101; C08L
95/00 20130101; C08L 95/00 20130101 |
Class at
Publication: |
106/273.1 |
International
Class: |
C08L 095/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 25, 2000 |
NO |
20000955 |
Claims
1. A process for preparing a warm mix asphalt composition
comprising mixing a grained aggregate material with a soft binder,
and adding a foamed hard binder to said mixture of grained
aggregate material and soft binder.
2. The process according to claim 1, characterised by using a hard
binder component with a penetration less than 100 dmm (measured
according to ASTM D 5 at 25.degree. C.).
3. The process according to claim 1, characterised by using a soft
binder component with a penetration of less than 0.3 Pa.s at
100.degree. C. (measured according to ASTM D 2171 at 100.degree.
C.).
4. The process according to claim 1, characterised by heating the
aggregate to 60.degree. C.-1200 .degree.C. before mixing it with
the soft and the hard binder.
5. The process according to claim 1, wherein the foamed hard binder
is made in a separate foaming process characterised by the steps
of: heating unfoamed hard binder to a temperature between 130 and
180.degree. C.; providing water at a temperature between
5-80.degree. C.; and injecting 2-7% by weight water into said
heated unfoamed hard binder to expand said heated unfoamed hard
binder to a foam.
6. The process according to claim 1, characterised by using a foam
with a water content of 5% or less.
7. The process according to claim 1, characterised by adding the
soft binder component to the aggregate at a temperature of less
than 120.degree. C.
8. The process according to claim 1, characterised by the
temperature of the warm mix being in the range of 80.degree. C. to
115.degree. C. after mixing.
9. The process according to claim 1, characterised by using a dense
graded asphalt composition as the warm mix asphalt composition.
10. The process according to claim 9, characterised by using a
dense graded asphalt composition with a void content between 2% and
10% as the warm mix asphalt composition.
11. The process according to claim 1, characterised by using an
open graded asphalt composition as the warm mix asphalt
composition.
12. The process according to claim 1, characterised by using an
open graded asphalt composition with a void content between 14% and
26% as the the warm mix asphalt composition.
13. The process according to claim 1, wherein the soft binder and
the aggregate material is premixed in a warm process mixing
facility to a semi-finished product for transferral to an asphalt
laying site where upon a foamed hard binder is applied to the
semi-finished product in a production laying machine at the asphalt
laying site,
14. The process according to any of the preceding claim,
characterised by using bitumen components as the binder
components.
15. Use of the asphalt composition as prepared by a process
according to any of the preceding claims for paving
applications.
16. A system for preparing the warm mix asphalt composition of
claim 1, comprising a drying drum for heating and drying the
aggregate component, a mixing mill for mixing the asphalts
components and a mix storage silo, characterised by the system
further including foam production facilities for foaming the hard
binder before introduction to the mixing mill.
17. The system according to claim 16, characterised by the foam
production facilities comprising heating means for heating the hard
binder component and water or steam introducing elements for
subsequent introduction of water to the hard binder to produce a
foam.
Description
[0001] The present invention relates to a process and a system for
preparing a warm foam mix asphalt composition.
[0002] Asphalt mixes used for road building or paving in general
consist of mixtures of stone/gravel, sand, filler and binder
components. The binder components are referred to as bitumen for
the purpose of this specification, but other binder components may
be equally applicable. The bitumen components may be naturally
occurring bitumen, or derived from a mineral oil. The sand,
stone/gravel and filler are referred to as aggregate material or
aggregate grain material
[0003] The bitumen acts as glue for the mineral aggregate
components. Bitumen is a small fraction of a total asphalt mix,
typically between 4 and 7% by mass (or 10 and 15% by volume).
[0004] Asphalt compositions are normally divided into two main
categories, namely <<hot mix>> asphalt and <<cold
mix>> asphalt. A third less common "warm mix" asphalt has
also been used, as will be described in more detail later.
[0005] Hot mix asphalt has better overall properties than die cold
mix asphalt, and is for this reason used on roads with much
traffic. In production of hot mix asphalt the aggregate material is
heated before the hot binder material is added to the aggregate for
mixing.
[0006] Hot mix asphalt production typically takes place at
temperatures between 150.degree. C.-190.degree. C. and laying and
compaction on the road typically take place at temperatures between
130.degree. C.-160.degree. C. In some cases even higher
temperatures are prescribed. The bitumen and mineral aggregates
need to be heated due to several reasons. The aggregates need to be
dry, the bitumen needs to have a low viscosity to coat and adhere
properly to the aggregate components and the asphalt mixture needs
to have sufficiently low mix viscosity to enable laying, spreading
and compacting on the road. The type of asphalt mix and the grade
of bitumen largely govern the production temperature. Hot mix
asphalts gains their final strength/stability more or less right
away. Therefore a road with a hot mix asphalt can bear traffic more
or less immediately.
[0007] The heating of the asphalt's constituents is normally done
with fossil fuels, and this may produce environmentally unfriendly
gasses and dusts, uses non-renewable resources and adds to the
overall costs of the asphalt. Additionally, handling of asphalt at
high temperatures constitutes a potential safety hazard.
[0008] Cold mix asphalt is cheaper, easier to apply, more
environmentally friendly, than the hot mix asphalt. In production
of cold mix asphalt, the aggregate material is cold and moist when
it is mixed with a hot or cold binder material. To ease the mixing
of cold mix asphalt, the binder is often foamed before it is mixed
with the cold and moist aggregate material.
[0009] Various ways of producing foam bitumen are disclosed in
Norwegian patent application NO 85387 and the international
application WO 95/22661. Unfortunately the technologies relating to
cold mix asphalt result in mixtures with poor quality as compared
to conventional hot mix asphalt mixtures. This is attributed to a
variety or factors such as poorer coverage of aggregates with
bitumen, presence of water in the asphalt mixture, and poorer
spreading and compacting ability of the asphalt mix. This causes
these asphalt mixes to be highly permeable to water and air which
makes the final road surface susceptible to fretting, which means
that loose coarse aggregates are lost from the road surface rather
easily. Cohesion is also reduced and this may ultimately result in
collapse of the material and lack of internal stability. This is
often visible at the road surface and is known as rutting. Cold mix
asphalts needs a certain curing time necessary to build up the
strength of the mixture. The curing time can typically be from days
to months. This in turn results in more rapid deformation, cracking
and surface deterioration of an asphalt surface for the
above-mentioned reasons, cold mix asphalt arc typically used for
roads without much traffic in, for example, the Nordic countries
and Australia.
[0010] To overcome some of the above problems. WO 97/20890 suggests
a <<Process for preparing an asphalt composition>>
where asphalt is produced at somewhat lower temperature than in the
traditional hot mix process. The use of lower temperatures is made
possible by using the bituminous binder in separate parts, namely a
hard and a soft component. Together the hard and the soft
components form a bitumen which fulfils normal and specifications.
The soft component can be mixed with the mineral aggregates at much
lower temperatures (60.degree. C.-130.degree. C., preferably
90.degree. C.-110.degree. C.), The hard bitumen component is
subsequently dispersed into this mixture in powder or emulsified
form. Typically the `hard` bitumen component has a penetration of
50 dmm or less. The temperature of this component may typically be
between 20.degree. C. and 70.degree. C. This process yields an
asphalt mixture that can be laid, spread and compacted at
temperatures between 70.degree. C. and 100.degree. C. Lab and field
trials have shown good performance of these asphalt mixtures.
Asphalts such as this, with reduced mixing temperature as compared
to the hot mix, are for the purpose of this specification called
<<warm mix>>.
[0011] However, warm mix asphalt mixtures using emulsions have
proved to be expensive and complicated to use during production,
mixing, laying and compaction Asphalt compositions prepared from
bitumen emulsions require a bitumen/aggregate mixture with a
relatively high content of voids to allow the water to escape
during the breaking of the emulsion, compaction and service. An
emulsion used in this process typically contains 30-50% water. A
bitumen emulsion is very expensive to produce both in terms of
product costs and equipment costs for the contractor because of the
need for an emulsion factory and extra storage tanks at the asphalt
mix plant. Transportation of emulsions is less cost-efficient due
to the transportation of 30-50% water. Transportation of the
increased mass also contributes to an increase of emission of
environmentally unfriendly substances.
[0012] The production and handling of bitumen emulsions requires
some additional measures because of the chemicals used in
production, the frost sensitivity of the end product and the
requirement for separate tanks.
[0013] Hence, there is a need for an asphalt mix that has the
quality of the hot mix asphalt, but with the environmentally
friendliness, cost and ease of handling of the cold mix asphalt.
Growing health, safety and environmental awareness with the general
public and within industry has resulted in significant efforts
aimed at reducing the use of non-replenishable fossil fuels,
conserving energy and consequently reduce emissions. In the asphalt
industry reduction of hot asphalt mix production temperatures will
assist to get doser to this aim.
[0014] Accordingly, the present invention provides an asphalt
composition that can be produced at lower temperatures than the hot
mix, with lower energy input, with equal or better mechanical
properties, and at the same or lower costs. This is, achieved with
a process for preparing a warm mix asphalt composition comprising
mixing a grained aggregate material with a soft binder, and adding
a foamed hard binder to said mixture of grained aggregate material
and soft binder.
[0015] FIG. 1, shows a schematic comparison of asphalt mix
production routes comparing <<Conventional Hot Asphalt Mix
Production>> with the <<Warm Foam Asphalt Mix
Production>> of the invention; and FIG. 2, shows an example
of a method to foam a hard hinder. After the mixing of the various
components, the hard binder and the soft binder will merge to form
a binder component with the properties aimed at. The foaming of the
hard binder reduces the viscosity and enables proper coating and
adhering of the binder to the aggregate components at a lower
temperature.
[0016] The use of a foamed hard binder has significant economical
and environmental advantages over the use of a bitumen powder or
emulsified form of bitumen, without being detrimental to the
quality of the resulting asphalt mixture and pavement. The water
content is only 2-5% as compared to the previously mentioned 30-50%
of an emulsion. This has a significant effect in terms of storage,
quality, heat requirements and transport. Compared with emulsified
binders the lower water content of foamed bitumen enables immediate
curing with limited heating.
[0017] Compared to the cold mix foamed asphalts, the asphalt made
with the process of the invention gives dense asphalt mixes with
much lower void contents than the cold mix asphalts produced with
foamed binder components. The binders used in cold foam mixes have
a soft penetration, between 180 dmm and 700 dmm.
[0018] Additionally, the `hard` bitumen component as used in an
emulsion has typically a penetration of 50 dmm or less, compared to
a maximum penetration value of the foamed hard bitumen in the
invention of less than 100 dmm depending on the actual
application.
[0019] To compare the asphalt mix of the present invention with a
cold mix asphalt where a binder foam is used, it should be
emphasized that the mix of the invention can be applied on heavily
trafficked road, whereas cold mix foam asphalt only can be used on
low-traffic roads. This is due to the bitumen used in the
traditional cold foamed mixes being a bitumen with high penetration
values between 180 and 700 dmm). The final grade of bitumen used in
the process of the invention can be harder, with a typical
penetration from 60 to 250 dmm. The preparation of a cold mix
asphalt usually takes place in-situ--i.e. on the road--at ambient
(cold) temperatures were as the asphalt prepared according to the
invention can be done in the asphalt plant and/or on the road and
done at typically 60-100.degree. C. This immediately influences the
applications and applicability of these asphalt mixes.
[0020] In the present invention both an emulsified and a
non-emulsified soft binder component can be used, but the
non-emulsified soft binder is preferred. If an emulsified soft
binder is used, the emulsified soft binder contains a large amount
of water. This water must be expelled from the mixture before full
co-hesion and strength of the mixture is achieved. The emulsion may
either be a cationic or an anionic emulsion.
[0021] The hard binder component is added to the mixture as a foam.
The soft binder may also be added as a foam if this is found to
have advantages in a specific situation.
[0022] The soft binder component can also be added to the aggregate
at a relatively low temperature, i.e. a temperature of less than
120.degree. C.
[0023] The soft binder will normally be added to the aggregate at a
temperature of at least 70.degree. C., preferably at a temperature
in the range of from 60 to 130.degree. C., more preferably in the
range from 90 to 110.degree. C.
[0024] In this application, a soft binder component is defined as a
binder component having a penetration of at least 200 dmm
[0025] Suitably, the soft binder component has a penetration of at
least 500 dmm, preferably at least 700 dmm and more preferably at
least 800 dmm. (measured by ASTM D 5 at 25.degree. C.). Such binder
components are often characterised by their viscosity (determined
by ASTM D 2171 at 100.degree. C.) The soft binder component has a
viscosity of less than 0.300 Pa.s, preferably less than 0.200
Pa.s.
[0026] The asphalt prepared in the present invention is mainly
intended for road use, but other use should also be considered to
be within the scope of the invention.
[0027] The dense graded asphalt made in the process of the present
invention has preferably a void content of less than about 10% and
even more preferably a void content in the area between 3 and
10%.
[0028] The asphalt made in the process of the present invention
could also be open graded asphalt with a void content approximately
between 15% and 25%.
[0029] An embodiment of the invention will now be described by way
of the following example.
[0030] Schematic comparison of process routes is given in FIG. 1,
and a method for foaming the binder, in FIG. 2. A comparison of
quality and costs is given in tables II and I.
[0031] An asphalt production facility for producing asphalt mixes
(FIG. 1.) uses the process of the invention and comprises a drying
drum, a mixing mill, a mix to storage silo and bitumen foam
production facilities. Stone/sand is introduced to the drying drum
and is heated to approx. 130.degree. C. The warm stone/sand is then
led to the mixing mill where it is mixed with a soft bitumen at
approx. 120 .degree. C. When the soft bitumen is properly mixed
with the stone/sand, the hard bitumen foam is added to the mixture,
and mixing continues until finally the filler is added to the
mixture at approx. 20.degree. C. The product comprises approx., by
mass, 90% stone/sand, 2,5% soft bitumen, 2,5% hard bitumen and 5%
filler.
[0032] The foam is made (FIG. 2) by letting a controlled flow of
hot bitumen into a piping system through a first valve (A). The
valve first (A) allows circulation to storage, and this ensures a
stable temperature, required in the system. The temperature of the
tubing system is controlled and maintained by surrounding the
piping with hot oil or heater cable, and isolation. The temperature
selected is dependent on the quality, hardness and required
increase of volume of the bitumen. The temperature is typically in
the range from 130.degree. C. to 180.degree. C.
[0033] Controlled flow of water, cold warm (5.degree. C.-80.degree.
C.), is led through a second valve (B) and is added to the bitumen
in an amount in the order of 2-7%. By injecting the water into the
bitumen flow, the bitumen expands. The bitumen is homogenised in a
static mixer in a mixing chamber. Expanded bitumen, typically with
a 10 to 20 times increase of volume, is led out of the mixing
chamber through an outlet and is added to the aggregate mixture
through one or several nozzles.
[0034] By comparing this process with a standard hot mix process
producing asphalt of the same quality, it was found that the
CO.sub.2 emissions where 60-70% lower, dust emissions where 30-40%
lower and fuel consumption 40-60% lower.
[0035] The tables I and II below, shows a relative quality
comparison with hot mix, and a relative cost comparison,
respectively, The <<=>> indicates average or equal,
<<+>> indicates equal or above average, and
<<->> indicates worse or lower than average in table I.
The <<?>> indicates an uncertainty,
<<unknown>> or not measured.
1TABLE I Relative Quality comparison with Hot Mix Warm Mix Warm Mix
Emulsion Foam Cold Mix QUALITY Stability = - - Adhesion - + -
Cracking - = = Durability - + - Workability = + - ENVIRONMENTAL
EFFECTS Fuel 40-60% less 40-60% less ? CO2/CO emission, dust 40-70%
less 40-70% less emission 30% less 30% less HEALTH ASPECTS Working
at Asphalt Plant 60-80.degree. C. less 60-80.degree. C. less
100-160.degree. C. less Working at laying 60-80.degree. C. less
60-80.degree. C. less 80-140.degree. C. less VOC levels Reduced
Reduced 0
[0036]
2TABLE II Relative Cost comparison (Hot mix = 1.0) Warm Mix Warm
Mix Emulsion Foam Cold Mix COST Aggregates 1.0 1.0 1.0 Fuel 0.5 0.5
0 Binder (emulsion/dopes etc) 1.5 1 1.5 TOTAL COST 1.2 0.9 0.9
[0037] The above non-limiting example is but one embodiment of the
invention, and it should be understood that other embodiments could
be performed, still within the spirit and scope of the present
invention. The invention should only be limited by the following
appended claims.
* * * * *