Compositions: coating or plastic – Coating or plastic compositions – Bituminous material or tarry residue
Patent
1992-10-19
1995-12-12
Lieberman, Paul
Compositions: coating or plastic
Coating or plastic compositions
Bituminous material or tarry residue
2523115, 252319, 252328, 252332, 252341, C08L 9500, B01J 1300, B01D 1704
Patent
active
054746078
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method for improving bitumen emulsions and to an improved bitumen emulsion. More particularly, this invention relates to improvements in respect to bitumen emulsions that may be used for sealing.
Bituminous emulsions were one of the earliest forms for sealing of roads and still remain as a common means for sealing roads. In more recent times, a change to hot spraying of bitumen Came about due mainly to economic and also technical reasons. Technical problems associated with emulsions related to run-off, limits on bitumen level and to cure time. This particularly limited emulsion use for re-sealing of roads. The economic advantages of spraying bitumen were more evident. Despite the problems associated with emulsions referred to above there are other technical advantages that make them attractive despite these drawbacks.
One such development includes the EVERSEAL (TM) emulsions which were used where hot bitumen was not an alternative.
The initial trials in respect to use of this emulsion produced success which created impetus to continue with the trials. It was found however that when a 70% emulsion was sprayed in cold conditions with high wind chill, the emulsion was caused to flocculate into a cheesy state which will not wet the stone. These results were confirmed in further trials where in all cases the pavement temperature was below 9.degree. C. and the wind chill was significant and was found that the emulsion did not wet either the pavement, stone or both.
These trials lead to an investigation on the basic mechanism of emulsion behaviour under cold conditions. It was thought the cutter content could stabilize emulsion against flocculation. However, the addition of higher levels of cutter presents a long term problem of binder softening and potential bleeding. Thus a number of new formulation tools were required. These included changes in manufacturing techniques and equipment in addition to the changes in respect to the chemical formulation. Applicational parameters were also modified to better suit the requirements of the emulsion.
This work led to an extension in the range of conditions which could be accomodated in the field. Trials were successfully carried out with pavement temperatures down to 6.degree. C. It was felt that it was more due to wind chill factors, which could not be withstood that caused the cheesy effect reducing stone retention in the bitumen.
The problem was initially overcome by use of polymer modification. With such materials, pavement temperatures of as low as 4.degree.-5.degree. C. with wind chills of 5.degree. C. have been accomodated. It was felt that one extremely important effect of the polymer modification is that rubber modified sealing can be done in cold conditions and the polymer provides green strength to decrease the tender or cure period.
Since the time that the Everseal Emulsion range was first developed it became evident that the curing time, particularly in poorer conditions needed to be faster.
The present invention attempts to overcome or at least alleviate one or more of the problems associated with these previous processes.
In particular, the present invention resides in a method of modifying bitumen emulsions wherein the method comprises the initiation of coalesence of the emulsion by either i) the addition of a specific chemical agent to the emulsion; or ii) physical reaction.
It is preferred that the initiation of coalesence is as a result of an increase in binder content for the emulsion.
It is particularly preferred that the bitumen emulsion is modified by the combination of a pre-emulsion solution of finer particle size distributions to replace part of the aqueous phase of a primary emulsion solution. This produces at least a bimodal particle distribution having improved packing and stability compared to a single distribution.
The invention further resides in an improved bitumen emulsion produced by the method as indicated above and to a bitumen emulsion having a binder content of at least 75% by weight of the binder.
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Emoleum (Australia) Limited
Hailey Patricia L.
Lieberman Paul
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