COATING OF SURFACES WITH BITUMINOUS MEMBRANES

Abstract: A method of treating a surface with a sprayed composition including bitumen to form a membrane and which comprises providing a raw material supply of bitumen which is heated to 140 DEG C, and an alkaline supply of blending water which are heated and then blended to form a blended mixture/emulsion, and then pumped when required through a first delivery line to a first discharge head, and a further supply of water which is treated to be acidic is pumped along a second delivery line to a second discharge head, in which the first and second discharge heads are positioned close to each other and arranged to direct respective streams of the blended mixture and the acidic water to impinge one upon the other downstream of the delivery heads to form a dispersed spray which is then applied to the surface to be treated, and which then cures rapidly to form a membrane on the surface. The method of the invention and the components of the spray composition enable bituminous coatings to be applied without need for high temperature application as used in existing hot coating application of asphalt bitumen.

Description: COATING OF SURFACES WITH BITUMINOUS MEMBRANES This invention is concerned with the coating of a surface with a bituminous membrane in order to render the surface resistant to penetration by water. There are many applications in which it is necessary to apply water-resistant coatings to surfaces, such as the inner linings of tunnels, flat roofs, storage tanks, sea defence applications, repair of concrete surfaces etc, and present techniques require a raw material feedstock of asphalt bitumen (which is semi-viscose at ambient temperature) to be heated to a substantial temperature (e.g. about 130°C), and then while still hot is applied as an asphalt coating to the surface concerned. It is important to apply the coating while the asphalt is still sufficiently hot, so that it can flow over the surface and fill any crevices, and thereby coat the surface evenly and without leaving any unprotected areas. If the asphalt should be allowed to cool too much before application, it can become difficult to handle and an unsatisfactory coating may result. Therefore using present techniques, typical coating rates (by trowelling) of only about 20 square meters per hour per man are achievable with a typical team of operatives. The present invention utilises the surprising discovery that bitumen can be treated in such a way that it can be rendered flowable at less elevated temperatures above ambient temperatures than is required for present hot coating application of asphalt bitumen, and such that the treated bitumen can be applied in sprayed form thereby increasing significantly the rate of application to a surface to be treate . The Applicants have found that a raw material feedstock of bitumen, such as a blend of 50 / 200 PEN bitumen, can be heated and then blended with heated water in a predetermined pH range (at least slightly alkaline and preferably of pH range of 8.5 to 12.5 dependent on ambient air temperature), and subsequently stored at a lower (above ambient) temperature and which can then subsequently be withdrawn from store and, using a novel spray coating technique, can then be sprayed onto a surface to be treated to form a membrane. Accordingly, in general terms the invention provides a method of treating a surface with a sprayed composition including bitumen to form a membrane thereon, and comprising: providing a raw material supply of bitumen, and an aqueous blending medium in a pH range which is at least slightly alkaline; heating the bitumen and the aqueous blending medium; blending the heated bitumen and aqueous blending medium to form a blended mixture / emulsion; pumping the blended mixture through a first delivery line to a first discharge head; and pumping a further aqueous supply which is acidic along a second delivery line to a second discharge head; in which the first and second discharge heads are positioned close to each other and arranged to direct respective streams of the blended mixture and the further acidic aqueous supply to impinge one upon the other downstream of the delivery heads to form a dispersed spray which is then applied to the surface to be treated, and which then cures rapidly to form a membrane on the surface. Preferably, the raw material supply of bitumen comprises a blend of 50 / 200 PEN bitumen, and the aqueous blending medium comprises water having a pH in the range 8.5 to 12.5. The further supply of water pumped through the second discharge head is acidic, and depending upon the nature of the water supply utilised, this may need to be treated to render it sufficiently acidic for use in the invention. The blended mixture of bitumen and alkaline water may be stored in storage drums at ambient temperatures ready for use, and can be pumped via the first discharge line at this temperature in flo able form, which compares favourably with existing techniques for hot application of asphalt. The blended mixture also desirably has certain suitable fillers incorporated therein e.g. bentonite powders, and with the unexpected advantage that at least to some extent an emulsion is formed, which is capable of being pumped and delivered as a spray which is able to flow readily over any surface to be treated, while at a temperature lower than that required for heated application of asphalt by conventional * techniques, and which cures rapidly to form a membrane. The reason why the introduction of acidic water (via the second delivery line) into a blended mixture of bitumen and alkaline water has surprisingly beneficial results in rendering the bitumen flowable at ambient temperatures (and rapidly curable upon application) is not entirely clear, although it is believed that there is some breakdown reaction within the components. The fact remains that this advantage is achieved, provided that the bitumen and the blending water are heated, the blending water is at least slightly alkaline preferably within the pH range 8.5 to 12.5 and the further supply of water via the second discharge head is acidic. The acidic pumped water supply delivered via the second discharge head creates a stream which impinges upon the stream of pumped blended bitumen mixture, and comes into intimate contact, globule to globule, and generates a dispersed spray which then is directed onto the surface to be treated. The water contained in the dispersed spray evaporates over a period of time, and the bitumen cures to form a durable water resistant membrane. A preferred additive to the aqueous blending medium is available from Epro UK Limited under the Trade Mark EPROPACK 2 and comprises latexes, soaps and provides "fatty acids" when required to increase the proportions of fatty acid derived from the raw material feedstock of bitumen, which is preferably Venezuelan bitumen of low acidity so that required subsequent break down can take place. The additive also includes components to render the blended mixture sufficiently alkaline that it can be stored subsequently at ambient temperature in flowable form. A preferred additive to the aqueous dispersing medium is available from Epro UK Limited under the Trade Mark EPROLYST 1 or 2, and which includes calcium salts, such as calcium chloride, and which renders the water sufficiently acidic e.g. in the range 2.2 to 4.5, having regard to the alkalinity of the blended mixture of emulsion, that a suitable reaction takes, place and a curable dispersed spra * y coating of bitumen results on the surface to be treated. One embodiment of the invention will now be described in detail, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a flow diagram showing the treatment of a bitumen feedstock to form a blended mixture suitable for subsequent spray coating application by a method according to the invention; and,. Figure 2 is a schematic illustration of the means whereby the blended mixture is pumped towards a surface to be treated by a sprayed coating of blended bitumen in the method according to the invention. Referring now to the drawings, a method of coating a surface to be treated with a blended mixture of bitumen and blending water which is at least slightly alkaline will now be described in detail. Figure 1 shows schematically the initial treatment of a bitumen feedstock, which is preferably a blend of 50 / 200 PEN bitumen of Venezuelan type, which is heated to 140"C and then stored in an insulated tank 10. The heated feedstock is then fed to a blending storage tank 11 at which a temperature of about 140 β C is maintained, and when required this is then fed to a blending pump 12 via feed line 13, and in addition there is also fed to the pump 12 via feedline 14 an aqueous blending medium comprising heated water from a storage tank 15, in which the water is heated to about 50 β C, and is treated to be at least slightly alkaline, preferably in the pH range 8.5 to 12.5. The blending pump 12 then mixes the raw bitumen feedstock and the water, together with fillers and any other necessary ingredients to assist at least partial emulsification, and the blended mixture / emulsion is then discharged via line 16 to a storage tank 17 which holds the blended mixture at a temperature which is maintained at about 90"C. Then, the blended mixture is transferred to storage drums 17a at ambient temperature. The proportion of bitumen to water will vary according to the ultimate flowability requirements, but a ratio of about 60% bitumen to 40% water has been found to be advantageous. However, this ratio is not absolutely critical, and experiments carried out with ratios of 70% bitumen to 30% water have been found to give advantageous results. It is envisaged that other ratios will give advantageous results, as determined by experiments, but the lower the proportions of water, the harder will be the membrane upon curing. When it is required to apply a sprayed coating composition to a surface to be treated e.g. wall of a tunnel, and which is shown schematically by reference 18 in Figure 2, the blended bitumen / water mixture / emulsion is fed from storage drum 17a along feedline 19 to a dispenser pump 20 which then pumps the mixture along a first discharge line 21 to a first discharge head 22 from which issues a pumped stream 23 of the mixture. A second dispersing supply of slightly acidic water, is fed to the dispenser pump 20 via feedline 24, and is pumped out separately along its own second discharge line 25 to a second discharge head 26, from which issues a pumped stream 27 of this second supply of acidic water. A preferred additive to the aqueous blending medium is available from Epro UK Limited under the Trade Mark EPROPACK 2 and comprises latexes, soaps and provides "fatty acids" when required to increase the proportions of fatty acid derived from the raw material feedstock of bitumen, which is preferably Venezuelan bitumen of low acidity so that required subsequent break down can take place. The additive also includes components to render the blended mixture sufficiently alkaline that it can be stored subsequently at ambient temperature in flowable form. A preferred additive to the aqueous dispersing medium is available from Epro UK Limited under the Trade Mark EPROLYST 1 or 2, and which includes calcium salts, such as calcium chloride, and which renders the water sufficiently acidic e.g. in the range 2.2 to 4.5, having regard to the alkalinity of the blended mixture of emulsion, that a suitable reaction takes place and a curable dispersed spray coating of bitumen results on the surface to be treated. The first and second discharge heads 22, 26 are positioned close to each other, and arranged to direct respective streams 23 and 27 which converge and meet at a region of impingement 28 at which intimate intermixing, globule to globule, of the respective streams takes place, and a dispersed spray 29 is formed which is applied to the surface 18 which is to be coated. Rapid curing of the material takes place, and a durable and substantially even bituminous membrane remains firmly adhering to the surface 18 to form a water resistant coating. It has been found in tests that a flowable coating composition including bitumen can be obtained by the method described above, at lower operating temperatures than normal practice of hot application of bitumen, and with substantial increase in rates of production of bituminous coatings. With one man operation, unhindered, coating rates of 1500 square meters per day can be achieved, and with a two man output, up to 3000 square meters per day can be achieved, with one man operating the pump. The pump rating is such as to be able to pump each of the liquid components supplied thereto to a height of 300 meters, equivalent to a 100 storey high block. Full adhesion of the coating products, after spray application, is achieved after about two hours. The coating composition may be applied directly to asbestos lined products, thereby avoiding the necessity to remove degraded fibres. In view of the enhanced flowability of the bitumen / water mixture, the discharge heads have extended life and routine cleaning is simplified. Conveniently, the dispenser pump 20 is mounted on a readily portable unit, such as a trailer or skid unit which is provided with all lines, spray equipment and filters. Conveniently, a single power source is provided which can provide drive input to a tandem arrangement of pumps, each having their own discharge lines and discharge heads, for two man coating applications. The means by which the bitumen feedstock is initially heated to 140°C has not been shown in the drawing, but conveniently a boiler rated at 27000 btu may be utilised. The application of the dispersed spray coating, shown schematically in Figure 2, may be achieved by connecting a dispenser pump via one quick fit coupling to a holding tank having a blended bitumen / alkaline water dispersion, and via a second quick fit coupling to a tank with an acidic aqueous solution e.g. water with additives to bring the acidity up to the required level. The pump comprises an engine driving a hydraulic gearbox and power pack unit, and having hydraulic systems which are switched through a series of control units controlling both pressure and the split of pressure to individual pumps. The pumps are cat pumps or similar based on a split manifold, three valve plunger system. These pumps are set at desired speeds of revolution, based on a ratio of approximately 1.75-2:1 against the water pump. The pumps are also associated with a pressure diverter switch which allows the operator to adjust the pressure of either the bitumen flow pump or the aqueous solution water pump. The split assists in increasing flow in certain conditions on site. These pumps are connected to two outgoing lines, one for bitumen and one for water which progress through specially designed air tight connections to a gun which has two nozzles, one for bitumen and one for water, which are set at desired angles and provided with required lengths. The nozzles contain two nipples of different diameters and set at different angles, to control the flow pattern of the bitumen, and can be set perpendicular to each other during application. Due to the design nature of the fittings, the pump does not require cleaning out through the bitumen lines of access lines into the pump system. However, a self cleaning tank may be attached via a short line to the bitumen pump which can be used to flush out and suspend bitumen for over night storage. This line is then flushed out through a short extension pipe with bitumen prior to use at the start of each working shift. The pump has engine speeds, hydraulic pressures, pump speeds and diverter all set at specific levels which, if adjusted, affect each and every application setting throughout the pump.

Claims: CLAIMS 1. A method of treating a surface with a sprayed composition including bitumen to form a membrane thereon, and comprising: providing a raw material supply of bitumen, and an aqueous blending medium in a pH range which is at least slightly alkaline; heating the bitumen and the aqueous blending medium; blending the heated bitumen and aqueous blending medium to form a blended mixture / emulsion; pumping the blended mixture through a first delivery line to a first discharge head; and, pumping a further dispersing aqueous supply which is acidic along a second delivery line to a second discharge head: in which the first and second discharge heads are positioned close to each other and arranged to direct respective streams of the blended mixture and the further acidic aqueous supply to impinge one upon the other downstream of the delivery heads to form a dispersed spray which is then applied to the surface to be treated, and which then cures rapidly to form a membrane on the surface. 2. A method according to Claim 1, in which the raw material supply of bitumen comprises a blend of 50 / 200 pen bi umen. 3. A method according to Claim 1 or 2, in which the aqueous blending medium comprises water treated to have a pH in the range 8.5 to 10.5. 4. A method according to any one of Claims 1 to 3, in which the blended mixture has fillers incorporated therein. 5. A method according to Claim 4, in which the fillers comprise bentonite powders. 6. A method according to any one of Claims 1 to 5, in which the blended mixture is maintained at a predetermined storage temperature in a storage tank ready to be pumped through the first delivery line when required. 7. A method according to any one of Claims 1 to 6, in which the raw material supply of bitumen is held in an insulated tank heated to 140 β C, prior to being supplied with the aqueous alkaline blending medium to a blending pump and discharged to a storage tank maintained at 90 β C, prior to discharge to storage drums. 8. A method according to any one of Claims 1 to 7, " in which the bitumen is Venezuelan type bitumen.

Inventors: TOWNEND IAN, TOWNEND, IAN
Applicants: EPRO UK LTD, EPRO UK LIMITED
Application year: 1992
Main classification: B05D1
IPC codes: C04B41, C08L95