Note: Descriptions are shown in the official language in which they were submitted.
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Goldschmidt AG, Essen
Method For Producing Foam 9itumen With Improved Foam
Stability And Improved Foam Volume
The invention relates to a process for producing foamed
bitumen having improved foam stability and improved
foam volume.
According to DIN 55 946 part 1 (12/1983) bitumen is the
term for the dark-colored, semisolid to rubbery,
meltable, high molecular mass hydrocarbon mixtures
obtained in the gentle processing of crude oils, and
the fractions of natural asphalts that are soluble in
carbon disulfide, and also mineral wax and montan wax.
Bitumen is used in architectural preservation as a
coating material or casting compound. Further areas of
application are in anti-groundwater sealants, as an
electrical insulating material, in the prepared roofing
industry, but primarily as a binder for a host of
organic and inorganic substrates, such as plastics,
paper, paperboard, recyclable materials such as
constructional rubble or slags from industrial
processes, problematic substances containing asbestos,
and, in particular, conventional roadbuilding gravels
and sands, crushed rock, and chippings.
Since the customary bitumens are solid at normal
temperatures, they must be liquefied in order to
produce a coating which adheres to the substrates.
This can be achieved by heating to appropriately high
liquefication temperatures. Disadvantages here are that
the operation is very energy-intensive and that as a
result of the evaporation of low-boiling constituents
in the bitumen there is a perceptible burden on the
environment.
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Although dissolving bitumen in appropriate organic
solvents circumvents these problems, it too has the
drawback that the solvent, on evaporation, burdens the
environment over a long period of time and, moreover,
raises toxicological concerns.
Replacing the solvent with water requires a
considerable proportion of surfactants in order to
produce stable, useful dispersions/emulsions. The
surfactants are leached by rainwater and hence, in the
long term, are likewise emitted to the environment.
Another method of using bitumen in roadbuilding is to
process it to foamed bitumen. Foamed bitumen is a term
used for bitumen which is foamed using water and air at
temperatures above 140 C and applied, as a mixture of
air, water, and bitumen, to the aggregates that are to
be bound.
Mineral materials bound with foamed bitumen offer
considerable advantages in roadbuilding as compared
with other, comparable technologies: foamed bitumen is
outstandingly suitable for stabilizing mineral
materials and sands. The foam binds immediately to the
surface of the aggregate, especially to the fine
fractions of the mineral material mixture, and even
moist surfaces are adequately wetted.
Owing to their increased temperature stability and
deformation stability, the bitumen-aggregate mixtures
produced in this way (which are also referred to as
asphalt) are especially suitable as material for base
layers and binder layers in roadbuilding.
Additionally, however, there is also increasing
interest in recycling applications, such as the
encapsulation of materials from industrial processes,
such as blast furnace slags, metal slags, and
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phosphorus slags, and, in particular, problematic
materials containing asbestos.
In order to wet and/or encapsulate the mineral
materials effectively, the bitumen foam must comply
with two fundamental prerequisites: on the one hand, a
sufficiently large foam volume, and also a sufficient
stability before the foam collapses on itself to a
marked extent.
These criteria, the degree of expansion and the so-
called half-life (the time within which the maximum
foam volume has contracted by 50%), are critical
characteristics of bitumen foam and depend on a
multiplicity of interdependent parameters, for which at
the present time there are only inadequate explanations
or estimations.
Through the addition of additives attempts have been
made to improve foam volume and foam stability further
in the direction of the requirements of the art, since
when aggregates are added, especially mineral
aggregates, the contraction process is greatly
accelerated.
Thus JP-A 2000219762 (CA 133:154518) describes
quaternary ammonium salt additives which are based on
relatively long-chain amines and alkylimidazolines and
which are added in amounts of from 0.01 to 10% by
weight to the bitumen.
JP-A 62172039 (CA 108:76723) dissolves bitumen in
miscible solvents such as trifunctional polyether
polyols and foams the solution using amine-containing
and tin-containing catalysts, and also water and
silicone oil, to form polyurethane foams.
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JP-A 61115956 (CA 105:119752) mixes bitumen with
butadiene-styrene rubber and an azodicarboxamide
blowing agent and heats the mixture to 160 C.
The foams obtained are intended to have an improved
dynamic stability.
Also of considerable significance, furthermore, are the
origin of the bitumen, its quality, and the refinery
process. The reasons for inadequate foam formation and
foam stability are not always evident, since the
composition of the bitumen is complex and the refinery
processes use antifoams such as silicones, for example.
It is assumed, however, that these silicones have an
adverse effect on the foam behavior.
Surprisingly it has now been found that, contrary to
experience existing to date, certain silicone compounds
are not only capable of not adversely affecting volume
and stability of foamed bitumen but also, on the
contrary, in fact have a positive effect.
One object of the present invention, improving the
stability and volume of foamed bitumen, is achieved
through the use of special silicone compounds as
additives for their improvement.
The invention accordingly provides a process for
producing foamed bitumen from bitumen, water, and
additives, which comprises using as additive at least
one silicone compound of the general formula
F 3 [H3 H3
~ H3 1 H3 ' H3 IH
R-Si- Si=O Si=O Si O i i-O Si-R
CH3 CHs CH3 CH3
a CH3-Si-CH3 CH3 Si-CH3 a
RZ b c g2 bl ct
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in which
R, R1 and R2 in the average molecule can be identical or
different and denote an alkyl radical having 1 to
30, preferably 8 to 22 carbon atoms or the radical
-Z- ( CnH2n0- ) R3 , where
R3 is a hydrogen radical or an alkyl radical
having 1 to 8 carbon atoms,
Z is a divalent radical of the formula -0-,
-( CH2 ) F,-O- or -CH2-CH ( CH3 )-CH2-0- with p = 2 to
6,
n is an average numerical value from 2.7 to 4.0,
m is an average numerical value from 5 to 130,
a and a' together have an average numerical value from
4 to 1500,
b and b' together have an average numerical value from
0 to 100, and
c and c' together have an average numerical value from
0 to 50.
In the formula, R preferably has the meaning of a
methyl radical, R' preferably the meaning of an alkyl
radical having 1 to 30, in particular 8 to 22 carbon
atoms, and R2 that of a polyether radical, in which Z is
-0- or -(CH2)p-0-, with p = 3 or 4. This then gives for
the polyether radical the formula -(CH2) 3-0- (CnHznO-)mR3
and/or -(CH2)4-0- (CH2O-)R3 -
n has an average numerical value of 2.7 to 4.0, a
numerical value of from 2.7 to 3 being preferred. This
average numerical value arises during the preparation
of the polyether by a blockwise or random addition
reaction of corresponding amounts of ethylene oxide and
propylene oxide, it also being possible, if desired, to
use higher alkylene oxides, with one of n =
approximately 2.7 to 3.5.
m has an average numerical value from 5 to 130 and
indicates the average number of oxyalkylene units in
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the polyether radical. Preferred for m is an average
numerical value from 6 to 50_
R3 is a hydrogen radical or an alkyl radical having from
1 to 8 carbon atoms. Particular preference is given to
an alkyl radical having from 1 to 5 carbon atoms,
especially the butyl radical.
The indices a, a', b, b', and c, c' preferably have the
following values:
a and- a''together have an average numerical value from
4 to 800,
b and b' together have an average numerical value from
0 to 50,
c and c' together have an average numerical value of
from 1 to 30.
Especially preferred compounds are those in which R1 is
an alkyl radical having 6 to 22 carbon atoms, R2 is a
polyether radical - (CH2 ) 4-O-C2H40- ) mR3 and/or
-(CH2) 4-0-CH2-CH (CH3) -CH20)n,R3, in which m is an average
numerical value from 6 to 50, in particular from about
10 to 30, b and b' = 0, and the ratio (a+a'):c:c'=(10
to 200):(3 to 30):(0 to 10) in particular
(a+a'):c:c'=(60 to 80):(15 to 25):(0 to 5).
The invention further provides a bitumen foam produced
using at least one silicone compound of the general
formula
~~'H3 ~ H; ~3 ~ H3 j H3 ~ H3
R-Si- Sz*O i i"O S3.'O 3i-O 3i=R
CH3 CH 0 ~ CH3 CH3
3a [3.SlCHJ CH3-Sl--CH a `
Rl b c R2 3 ~ c
in which
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R, R1 and R 2 in the average molecule can be identical or
different and denote an alkyl radical having 1 to
30, preferably 8 to 22 carbon atoms or the radical
-Z- ( CnH2õO- ) mR3, where
R3 is a hydrogen radical or an alkyl radical
having 1 to 8 carbon atoms,
Z is a divalent radical of the formula -0-,
-(CH2) p-0- or -CH2-CH (CH3) -CH2-O- with p= 2 to
6,
n is an average numerical value from 2.7 to 4.0,
m is an average numerical value from 5 to 130,
a and a' together have an average numerical value from
4 to 1500,
b and b' together have an average numerical value from
0 to 100, and
c and c' together have an average numerical value from
0 to 50.
The invention further provides for the use of foamed
bitumen comprising at least one of the above compounds
for adhesively bonding substrates such as, in particular,
mineral materials which can be used in roadbuilding.
The invention further provides a foamable bitumen
mixture comprising bitumen, water, and additives,
wherein as additive use is made of at least one
silicone compound of the general formula
+ H C[H31 CH
3 1 3 ~3 i H3 ~3
R-Si- 1Si O Si O Si=O JSi-O Si-R
I
I I I
CH3 LCHJa CH3
CCa'
Rl b c R2 c
in which
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R, R1 and R2 in the average molecule can be identical or
different and denote an alkyl radical having 1 to
30, preferably 8 to 22 carbon atoms or the radical
-Z- (CnH2n0- ) R3, where
R3 is a hydrogen radical or an alkyl radical
having 1 to 8 carbon atoms,
Z is a divalent radical of the formula -0-,
-(CH2)p-0- or -CH2-CH(CH3)-CH2-0- with p = 2 to
6,
n is an average numerical value from 2.7 to 4.0,
m is an average numerical value from 5 to 130,
a and a' together have an average numerical value from
4 to 1500,
b and b' together have an average numerical value from
0 to 100, and
c and c' together have an average numerical value from
0 to 50.
Further subject matter of the invention is
characterized by the claims.
Surprisingly it has been found that with the
polysiloxane compounds used in accordance with the
invention it is also possible to foam bitumens which do
not normally. produce foams which can be used
industrially, since either the half-life amounts to
only a few seconds and/or the foam volumes are not
large enough. The technical properties of easy-to-foam
bitumens are further greatly improved through the use
of the compounds of the invention. This is all the more
surprising on account of the fact that in the art to
date these compounds are known to have been used as
defoamers.
The bitumen foam is prepared in principle by injecting
a mixture of air and small amounts of cold water (about
1 to 5% by weight, based on bitumen) into an expansion
chamber along with bitumen heated to about 140 to 200 C.
The water evaporates explosively and forces the mixture
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with high pressure through an atomizer die, generating
a bitumen foam having a volume about 15 to 25 times
higher than that of the initial bitumen. This foam is
applied to the aggregates.
In order to wet these aggregates effectively the
bitumen foam must, as a fundamental requirement, have
in particular, on the one hand, a sufficiently high
volume (degree of expansion) and, on the other hand, a
sufficient stability (half-life). Consequently, these
criteria are also employed for assessing the foam
quality.
The expansion ratio (Ex) is defined as the ratio of the
maximum foam volume [Vmax] to the volume of the bitumen
[Vmin]: Ex =[Vmax]/[Vmin]. The volumes are determined
by a measuring rod to an accuracy of 1 cm.
The half-life (T1/2) is the time within which the foam,
after reaching the maximum volume, shrinks back to half
the maximum volume. The respective foam volume is
determined by means of a measuring rod, while the time
is determined by means of a stopwatch and measured to
an accuracy of 1 second.
The aim is for a foam with as high a volume as possible
which at the same time has as long as possible a half-
life. Since both values enter into the assessment of
foam quality, the foam index (FI) has been proposed as
a new quality criterion.
According to the paper by K.J. Jenkins, M.F.C. van de
Ven and J. de Groot at the 7th Conference on Asphalt
Pavements for Southern Africa, the evaluation of
laboratory results has to date ignored the fact that
the foam contracts even during the sprayout time and
therefore that the measured foam volume (ERm) may
deviate considerably from the actual maximum volume
(ERa), as a function of the half-life of the foams. In
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order to determine this ratio (ERm/ERa) a correction factor
(c) has been proposed, and is introduced into the formula
in order to determine the foa.., index FI:
FI =-T1/2 ERm - 41n 4 + l+c * ERm * ts
ln2 ERm 2c
FI = foam index;
ERm = maximum expansion rate;
T1/2 = half-life; time in sec within which the foam
volume has contracted by half;
ts = spraying time;
c = correction factor, taken from the conference
papers.
Figure 1 is a graph of the ratio of ERm to Era against
half-life measured in seconds, for various spraying times.
Since the foam properties are essentially dependent on the
type of bitumen used, the bitumen temperature, the air
pressure, and, in particular, the water content, the volume
flows passed into the expansion chamber and also the
experimental conditions must be carefully attuned to one
another. Operation takes place generally at bitumen
temperatures of about 140 to 200 C, water contents of about
1 to 5% by weight, based on bitumen, and an air pressure of
up to about 5 bar.
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In order to improve the performance properties of the
foam, adjuvants and auxiliaries may be added to the
water used as blowing agent. The additives used in
accordance with the invention are likewise preferably
admixed to the water, the amounts being in the range
from about 0.01 to 5% by weight, preferably from about
0.02 to 2% by weight, based on bitumen.
In accordance with the invention it is possible in
principle to foam any bitumens. The choice of the type
used is determined primarily by the technical
application. Preference is given to the grades which
are commonly used in roadbuilding, i.e., 15, 25, 45,
65, 80, 200, 300, and 400, and especially bitumens with
a penetration rating of 70 to 200 (type B 80 to type B
200).
Experimental procedure:
The examples below were carried out using a type B 200
E bitumen from the company NYNAS. The experiments were
carried out using the foamed bitumen laboratory unit
WLB 10 from Wirtgen, D-53578 Windhagen, Germany, in
accordance with the given operating instructions.
Introduced into the expansion chamber were the bitumen,
heated to 170 C, with a pressure of 6.5 bar, the air,
with a pressure of 6 bar, and the water (20 C) , with a
pressure of 5 bar. The batch size was in each case
500 g, the bitumen flow rate 100 g/sec, the spraying
time 5 sec, and the amount of inventively co-used
additive 0.025% by weight, based on bitumen. The stated
measurement values are averages from three
measurements.
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Experimental results:
Additive 1 Additive 2
Water ERm T1/2 ERa FI ERm T1/2 ERa FI
% by
wt.
1.0 8.4 364.8 8.4 784 8.1 336.6 8.1 650
2.0 20.2 158.7 20.4 2320 19.6 139.4 19.9 1963
3.0 27.8 69.0 28.6 1741 27.2 57.7 28.1 1431
4.0 31.1 30.0 33.1 978 30.7 23.9 33.2 799
4.0 30.1 13.1 34.8 505 30.4 9.9 30.4 429
Additive 3 Additive 7
Water ERm T1/2 ERa FI ERm T1/2 ERa FI
% by
wt.
1.0 8.6 324.9 8.6 751 8.1 417 8.1 798
2.0 22.3 120.0 22.3 2097 21.7 272 21.9 4421
3.0 31.6 44.3 33.5 1399 32.2 178 32.5 5243
4.0 36.5 16.4 40.9 754 39.6 116 40.2 4615
5.0 37.1 6.0 50.1 427 43.8 76 44.9 3521
Additive 9 Additive 10
Water ERm T1/2 ERa FI ERm T1/2 ERa FI
% by
wt.
1.0 8.4 389 8.4 834 8.0 80 8.2 183.
2.0 18.0 249 18.1 2948 19.4 35 20.5 560
3.0 23.5 160 23.8 2989 27.1 16 30.4 500
4.0 24.7 102 25.2 2104 31.3 7 40.6 372
14.0 21.7 66 22.3 1149 31.9 3 56.8 306
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Additive 11 Bitumen without
additive
Water ERm T1/2 ERa FI ERm T1/2 ERa FI
% by
wt.
1.0 8.4 67 8.6 179 10.1 57 10.4 246
2.0 15.5 32 16.4 359 15.9 30 16.9 357
3.0 21.4 15 24.2 345 20.1 16 22.6 330
4.0 25.9 7 33.6 295 22.8 9 28.0 281
5.0 29.1 3 51.9 277 24.0 5 34.3 238
In a comparison of the markedly improved FI values, the
experiments with additives 1, 2, 3, 7 and 9 show the
advantages when using the additives of the invention in
comparison with the noninventive additives 10 and 11
and with the pure bitumen without additive.
Definitions are as follows:
Additive 1 Polysiloxane BC 793 from Goldschmidt in
which b + b' , c + c' > 0 and R, R1 , and
R 2 are polyethylene oxide/polypropylene
oxide chains with molar weights > 1000,
Additive 2 Polysiloxane B 1484 from Goldschmidt in
which b + b' , c + c' > 0 and R, R1 , and
R 2 are predominantly polypropylene oxide
chains with molar weights > 1000,
Additive 3 Polysiloxane B 1959 from Goldschmidt in
which b + b' , c + c' > 0 and R, R1 , and
Ra are predominantly polyethylene oxide
chains with molar weights > 1000,
Additive 7 Polysiloxane TEGO Addibit FS 700 from
Goldschmidt in which b + b' , c + c' = 0
and R is -CH3, R' is a fatty alkyl
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radical, and R2 is predominantly
polyethylene oxide chains,
Additive 9 Polysiloxane TEGOPREN 6814 from
Goldschmidt in which b + b', c + c' = 0
and R is -CH3, Rl, and R2 are fatty alkyl
radicals.
Comparative experiments:
Additive 10 Si-free polyether with polyethylene and
polypropylene chains and a molar weight
> 1000,
Additive 11 Si-free polyether with polypropylene
chains and a molar weight > 1000.
