Road structure – process – or apparatus – Pavement – Including bed
Reexamination Certificate
2000-05-16
2003-07-08
Pezzuto, Robert E. (Department: 3671)
Road structure, process, or apparatus
Pavement
Including bed
C404S075000
Reexamination Certificate
active
06588974
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The invention firstly relates to bitumen (asphalt) or asphalt (asphalt cement) for the production of road surfaces.
SUMMARY OF THE INVENTION
Road surfaces are very widely produced in the form of asphalt or a mixture of bitumen with aggregates, such as sand, gravel, grit (round or crushed) or the like.
One aim in a road surface is to achieve high wear resistance. Furthermore, the deformation tendency should be low in order that unevenness, such as wheel tracks or the like, if possible does not occur, is slight or only occurs after a long period of use.
The invention is concerned with the technical problem of providing an improved bitumen or asphalt, in particular for the production of road surfaces.
This technical problem is firstly and substantially resolved wherein the bitumen or asphalt contains a proportion of paraffin obtained by a Fischer-Tropsch synthesis (FT paraffin) FT paraffins principally consist only of normal paraffins. More than 90% are usually n-alkanes. The remainder consists of iso-alkanes. The chain length is from C30 to about C100, with a gradation (solidification point, SP) from about 68 to about 105° C. The proportion of FT paraffin is preferably 0.5% or more, based on a bitumen content of the asphalt or based on bitumen as such. In practice, these percentages are based on the weight. However, they can also be per cent by volume. Surprisingly it has been found that a road surface produced using bitumen or asphalt modified in this way is significantly more durable. The formation of wheel tracks under the usual loads occurring in road traffic due to motor vehicles is significantly reduced compared with conventional road surfaces based on bitumen or asphalt. The strength of a road surface is dependent on various interdependent factors, in particular, inter alia, on the degree of compaction. Surprisingly, it has been found here that the addition of FT paraffin facilitates significantly greater compaction. Although the FT paraffins ultimately result in a harder form of the road surface, in the liquid state they simultaneously reduce the viscosity of the “binding material”, i.e. the bitumen. They act as it were as “fluidizers”. The grit used, round or crushed, is also of importance with respect to the strength of the road surface. In the case of crushed grit, high strengths can be achieved, attributable to the intermeshing of the individual grit particles. However, better compaction can be achieved in the case of uncrushed, round grit or gravel. In this connection too, the addition of FT paraffins has advantageous effects. The adherence of bitumen to the stone, such as precisely this grit or gravel, is improved. A particularly significant improvement can be achieved if—at least partially—oxidized FT paraffins are employed. Although this causes the solidification point to drop by about 5° compared with non-oxidized FT paraffins, the abovementioned adherence is significantly improved, enabling the use of round gravel or grit, at least to a certain proportion, without reductions in strength having to be accepted. The advantageous effect of oxidized FT paraffins is attributed to the functional groups (polarity) which they thereby provide.
In practice, the proportion of FT paraffins is in the range from 0.5 to 10 per cent by weight, preferably in the range from 2.5 to 7.5 per cent by weight, and further preferably about 4 to 5 per cent by weight, based on the bitumen. Regarding the FT paraffins, a preferred range of use is those having a solidification point from 90 to about 105° C.
Whereas standard asphalt, in the form of rolling asphalt, contains about 3 to 8% of bitumen, so-called mastic asphalt, which contains about 6.5 to 8.5% of bitumen, is also prepared. Bitumen grades of B45 or higher are usually employed here. In order to prevent settling of the mineral constituents during transport of mastic asphalt, it is necessary to effect constant stirring until final processing. In order to keep the viscosity low for this stirring, the mastic asphalt is kept at a relatively high temperature, namely at 200 to 250° C. Surprisingly, the addition of FT paraffins, as explained above, in an approximately equal ratio to the mastic asphalt (or the bitumen of the mastic asphalt) results in it being possible significantly to lower the temperature which is necessary to keep the mixture stirrable. Whereas temperatures of at least 220 to 250° C. were hitherto necessary, a reduction of 30° C. is possible on addition of FT paraffins. This lowering in the temperatures is at the same time accompanied by the considerable advantage that release of harmful substances is reduced.
In asphalt, such as mastic asphalt or even rolling asphalt, it has also been found that a significantly longer time is available for working or processing the asphalt. Surprisingly, it has been found that the processing of this asphalt was also possible at lower temperatures than hitherto. Besides the reduction in viscosity described above, this effect is also attributed to a latent heat storage effect of the paraffin. On phase conversion of the paraffin, heat liberation takes place without a reduction in temperature.
Furthermore, the invention also relates to a road surface consisting of a lower layer of sand/gravel (frost protection layer), a bituminous sub-base on top of the sand/gravel layer, an asphalt binder layer and an asphalt/concrete layer, more generally known as an asphalt pavement. With respect to a road surface of this type, the invention is concerned with the technical problem of achieving greater durability, in particular with respect to deformation resistance.
This technical problem is firstly and substantially resolved in respect of the road surface in that the bitumen of the asphalt pavement layer and/or of the bituminous sub-base contains a proportion of FT paraffins. The proportion of FT paraffins is preferably in the range from 0.5 to 10%; by weight, further preferably 2.5 to 7.5% by weight. However, volume percentages can also be used here.
Although not always regarded as necessary, it is also within the scope of the invention, as stated, to modify the upper pavement layer, i.e. the asphalt pavement, by addition of FT paraffins. In fact, it has even been found that addition of from 1 to 3% of FT paraffins to the asphalt pavement allows greater strength to be achieved, in particular owing to the greater potential for compaction. More recent knowledge even indicates that the addition of FT paraffins to the asphalt pavement layer is the most important factor with respect to the individual layers of a road surface.
The FT paraffins in this connection are FT paraffins having an SP from 68 to 105° C., preferably in chain lengths from C30 to C100 or even C105. The above comments, in particular also with respect to oxidized FT paraffins, apply in the same way here.
The invention is also concerned with a method for the production of a road surface with regard to the technical problem of achieving greater durability.
In this respect, the invention proposes admixing an asphalt mixture for the production of a bituminous sub-base and/or an asphalt binder layer and/or an asphalt pavement in road-building with bitumen containing a proportion from 0.5 to 10%, preferably 2.5 to 7.5%, further preferably 4.5%-5%, suitably in per cent by weight, of FT paraffins. The FT paraffins are preferably added to the liquid bitumen or to the asphalt in solid or liquid form. In respect of a solid form, the FT paraffins here can be, for example, in the form of granules, powder, flakes or pellets. In the flake form, a flake-like substrate is involved. The admixing with the bitumen or asphalt is further preferably carried out at a bitumen temperature from about 160 to 170° C. The aggregate, such as stone, gravel or grit, is then added to the bitumen modified in this way.
Overall, it has been found that a bitumen of this type has a higher softening point, with lower penetration. Indeed, the penetration is slightly lower than would have been expected. The softening point rises more quickly
Damm Klaus-Werner
Hildebrand Günter
Iversen Bruno
Matthäi Michael
Richter Ferdinand
Farber Martin A.
Pechhold Alexandra K.
Pezzuto Robert E.
Schümann Sasol GmbH
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