The present invention relates to a method for manufacturing granular mastic asphalt, in which filler and heated aggregate, in a first stage, are mixed with a partial amount of bitumen preheated into a liquid state, and the mixture allowed to cool to ambient temperature to form a granular semifinished product, whereupon the said semifinished product, in a second stage, is mixed with a remaining amount of bitumen heated into a liquid state, to form a granular mastic asphalt end product. Such mastic granular is primarily intended for use as a protective coating over welded seams between pipe sections in subsea pipelines, particularly for conveying hydrocarbons. However, it is suitable also in other applications where there is a need for transporting mastic asphalt in a cold state over longer distances.
The word "filler" is the technical term used to denote rock flour or stone dust, while "aggregate" is the technical term denoting mineral materials in the form of crushed rock, sand, etc.
GB patent 334 588 discloses a method for preparing mastic asphalt in blocs, intended for use as an ordinary paving asphalt. Here, firstly a coarse aggregate fraction is mixed with bitumen, then a fine aggregate fraction is added, optionally together with a remaining amount of bitumen, and finally filler material. The entire operation is performed in one stage without any intermediate cooling, and the resulting product is in the form of blocks - not granular. GB patent 1 494, 279, like the above GB 334 588, discloses a method of fabricating mastic asphalt in the form of solid blocks, where the essential aspect is the choice of the proportional amounts of the various components, bitumen, filler and aggregate, and the particle size of the latter.
A method of the introductory stated kind, for the manufacture of granular mastic asphalt, is known for PCT patent application, publication no. WO 97/24410. The mastic asphalt product resulting from this prior method is an improvement on the 2
Mastic asphalt product described in GB 1 494, 279, the improvement being that the product according to the PCT application appears in the form of a granular which, compared to the bloc-shaped mastic asphalt, requires less consumption of energy in manufacture and is more easily handled in use, such as described in the latter document. A drawback of this prior method, however, is a non-uniform composition of the mastic asphalt granular, tending to result in the formation of lumps.
It has now surprisingly been found that the above drawback of the technique according to the PCT application is practically eliminated by retaining, in the first mixing stage, not only a partial amount of the total amount of bitumen, but also a partial amount of the total amount of filler to be contained in the end product, as stated more fully in the appending claim 1. Thereby the undesirable lumping tendency is obviated and the ease of handling is correspondingly improved. More particularly, the method according to the present invention possesses the following advantages over the prior art according to the above PCT application:
What is bitumen mastic?
The drilling mud bentonite conform to American Petroleum Institute (API) specification 13A which yield approximately 120 to 280 barrels of 15 centiposes mud per ton, preferably about 180 to 240 barrels per ton. Typical bentonites with their trademarks are Hydraul-EZ; KWIK-THIK and Super-Gel-X. The use of non-treated bentonite in bituminous and other polymer binders is well known. The treated bentonite clay from drilling industries was discovered to be, surprisingly, an excellent component in water soluble systems of bituminous mastics and sealants for cold application.
Asphalt is a bitumen derived from a number of materials such as, for example, petroleum shale oil, gilsonite and the like. Asphalt is a thick, viscous mixture of compounds such as paraffin, cycloaliphatic and aromatic hydrocarbon and lesser amounts of heterocyclic compound containing sulfur, nitrogen or oxygen. Although asphalt can be obtained from natural sources, it is primarily derived as the residue of petroleum distillation of (e.g., the bottom product of vacuum distillation is of a topped crude). Although this invention is not limited thereto, it is preferred that the asphalt have a penetration (ASTM D5) at 77-degree F., dmm: ranging from about 5 to about 300 dmm and more preferably, from about 50 to about 160 dmm and conform in general to specification outlined by ASTM D312, D946 and/or D449.
Asphalt cutback is a mixture of asphalt bitumen and petroleum solvent. Petroleum solvents can be one of the following: kerosene, fuel oils, jet fuel, mineral spirit/Stoddard, naphtha, high flash aromatic, low flash aromatic, xylene, toluene and other petroleum solvent products. Of this invention the preferable asphalt cutback is a mixture of asphalt bitumen and mineral spirit/Stoddard solvent, the asphalt bitumen ranging from about 55 to 85 wt. %.
A process of producing water reducible bituminous mastics and sealants is as follows:
1. 4% to 11% treated bentonite clay was to be added into clean water in the mixer. When clay is dispersed, or high sheared in colloid mill, after mixing it turns into clay slurry. The viscosity of clay slurry is between 20,000 to 180,000 centipoise (CPS) at 77 deg. F.
2. Asphalt bitumen cutback consists of 60 to 80 percent asphalt and 20 to 40 percent mineral spirit Stoddard solvent.
3. The clay slurry and asphalt bitumen cutback are mixed together to form a soluble system.
4. An additive is added to enhance the stability of the soluble system.
5. Non-asbestos fiber is added to reinforce the soluble system mastics and sealer film strength. It also provides additional viscosity and texture.
Included are cellulosic paper, fiberglass, mineral fiber, polymer fiber, including polypropylene and polyethylene.
6. Non-reactive fillers commonly called pigment extenders are e.g. natural or calcined clay, mica and silica powder, slate powder, coal ash, fly ash, etc. are added to the system to improve film strength and product's consistency.
7. The elastomers impart buffering as well as tensile strength and elongation to the formulations and include SBR, SBS, SIBS, acrylic, styrene, neoprene, polyvinyl, etc.
EXAMPLE 1 The Preparation of Bituminous Mastic
% By weight
Treated bentonite clay slurry 3-60
Asphalt Bitumen Cutback 20-90
The asphalt emulsions useful as components in the tiecoat of this invention are dispersions of asphalt in water. These asphalt emulsions may also contain emulsifiers and stabilizers, such as for example soap or surfactant, which are anionic, cationic or nonionic. A useful asphalt emulsion, for example, is SS-1 h grade asphalt, an anionically-stabilized asphalt emulsion. The asphalt emulsions contain from about 35% solids to about 75% solids, more preferably from about 55% solids to about 65% solids and most preferably about 60% solids. Asphalt emulsions with less than about 35% solids have been found to be detrimental to tack, lower the viscosity below a usable level and unduly prolong the application of the tiecoat. Asphalt emulsions with greater that about 75% solids have been found to be detrimental to stability and increase the viscosity above a usable level. The asphalt emulsions have hardness from about 20 pen hardness to about 100 pen hardness and more preferably from about 20 pen hardness to about 40 pen hardness. Pen hardness values greater than about 100 are too soft for man roofing applications and contribute significantly to surface tack.
The latices used in the tiecoat of this invention may be formed from any monomer or mixture of monomers which yields a water-insoluble latex polymer with a glass transition temperature of less than about 10° C. In the dried state. For example, acrylic ester monomers, including methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, decyl acrylate, methyl methacrylate, ethyl methacrylate, isodecyl methacrylate, butyl methacrylate; acrylic acid, methacrylic acid, itaconic acid, Maleic acid, fumaric acid, styrene, substituted styrenes, butadiene, acrylonitrile, ethylene, vinyl acetate, and the like may be used. It is required that the glass transition temperature of resultant latex is less than about 10° C. so that the tiecoat composition, formed by admixture with the asphalt emulsion, is flexible enough to withstand the requirements of the mastic coating system which may experience exterior temperature extremes and concommitant substrate expansion and contraction. Some of the monomers may only be used with other monomers in a mixture because they alone would not give rise to a homopolymer whose glass transition temperature is less than about 10° C., such as for example methyl methacrylate, a monomer whose homopolymer has a Tg of 105° C.
In addition, conventional coating components such as, for example, pigments, dispersants, surfactants, coalescents, wetting agents, rheology modifiers, thickeners, drying retarders, biocides, antifoaming agents, colorants, waxes, and the like may be used in the latex of the tiecoat of this invention.
The latex polymer is incorporated into the asphalt emulsion at a level of from about 5% latex solids/95% asphalt emulsion solids to about 85% latex solids/15% asphalt emulsion solids, based on the % total solids of the admixture, more preferably from about 15% latex solids/85% asphalt emulsion solids to about 85% latex solids/15% asphalt emulsion solids and most preferably from about 15% latex solids/85% asphalt emulsion solids to about 50% latex solids/50% asphalt emulsion solids.
The overall level of solids in the tiecoat is from about 10% by weight to about 75% by weight of the weight of the tiecoat. We have found that if the total weight % solids is less than about 10% it is detrimental to tack, lowers the viscosity of the tiecoat below a usable level and unduly prolongs the application of the tiecoat. Total weight % solids greater than about 75% have been found to be detrimental to the stability of the tiecoat and increase the viscosity of the tiecoat above a usable level. The level of solids in the tiecoat is more preferably from about 40% by weight to about 60% by weight, based on the total weight %.
Applications of the tiecoat may be made to various substrates, such as for example, asphalt-containing substrates, bitumen-containing substrates or modified bitumen, cement/asbestos shingles or roofing panels, urethane foam roofing panels, deteriorated concrete, and the like. The tiecoat may be applied by conventional techniques, such as for example by brush, roller, airless spray, and the likes.
A tiecoat is applied to a substrate, such as for example a bituminous surface prone to releasing colored bodies which would otherwise migrate into and discolor a mastic topcoat if it were directly applied to the substrate or if it were applied to a non-latex modified asphalt emulsion tiecoat. The application of the tiecoat is an additional step in the application of the overall mastic coating system. It is essential that the tiecoat rapidly become low in tack so that the subsequent mastic topcoat can promptly be applied by operators walking on the tiecoat such that the overall application process is not unduly prolonged.
To ensure that tenders are based upon the specific grades of mastic asphalt required, it is essential that the asphalt contractor is given precise details of the BSS number and of the table and column number therein.
Natural rock aggregate mastic or limestone aggregate mastic.
The Standard applicable.
The type of asphaltic cement, which is usually defined by reference to the appropriate columns in the tables of the BSS.
In addition, the asphalt contractor must be advised, as appropriate, of:
The type of isolating membrane, eg sheathing felt, fiberglass tissue, kraft building paper underlay etc.
The material to be used fro surface reflective treatment, e.g., chippings, bituminous aluminium paint, acrylic colored paint etc.
Architects, engineers and quantity surveyors are recommended to include the following clause in their invitations to tender
Table of British Standards for mastic asphalt specifications indicating the asphaltic cement recommended in each case