This inventiΩn is CΩncerned with the fΩrmatiΩn Ωf a bituminΩus cΩmpΩsitiΩn fΩr applicatiΩn tΩ a surface in Ωrder tΩ render the surface resistant tc penetraticn by water by fΩrmaticn cf a membrane therecn.

There are many applicaticns in which it is necessary tc apply water-resistant ccatings tc surfaces, such as the inner linings cf tunnels, flat rDΩfs, stΩrage tanks, sea defence applicaticns, repair cf 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. 130°C), and then while still hΩt is applied as a ccating to the surface concerned.

It is important to apply the coating while it is still sufficiently hot, so that it can flew ever the surface and fill any crevices, and thereby ccat the surface evenly and withcut leaving any unprotected areas. If the material should be allowed to COΩI tΩΩ much before application, it can become difficult to handle and an unsatisfactory coating may result.

Therefore using present techniques, typical trowel- applied coating rates of only abΩut 20 square meters per hour 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 without requirement for it to be heated prior to application as a coating, and remain highly flexible in cured form, and such that the treated bitumen composition can be applied as a spray when blended with water as a catalyst, thereby increasing significantly the rate of application of the composition to a surface to be treated, and curing immediately to form a membrane thereon.

The Applicants have found that a raw material blended 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 between 8.5 and 12.5 depending on ambient temperatures, and subsequently stored, and which can then subsequently be withdrawn from store and, using a novel spray coating technique, can then be applied to a surface to be treated by a spraying technique to form a rapidly curing membrane on the surface.

Accordingly, the invention provides a method of forming a bituminous membrane for application to a surface in order to render the surface resistant to penetration by water and comprising: providing a raw material supply of bitumen, and an aqueous blending supply in a pH range which is at least slightly alkaline; heating the bitumen and the aqueous blending supply and blending them together in a blending unit to form a blended mixture / emulsion; and, storing the blended mixture / emulsion in a flowable form prior to supply to a spray coating device, together with a separate acidic aqueous dispersing supply to the device to form a dispersed spray applicable to said surface.

Preferably, the raw material supply of bitumen comprises a 50 / 200 PEN bitumen blend (preferably Venezuelan bitumen of relatively low acidity), and the aqueous blending supply advantageously has a pH in the range 8.5 bo 12.5, and preferably comprises a supply of blending water treated) by a suitable additive to a required level of alkalinity.

However, other blends of bitumen than supplies of 50 and 200 PEN bitumen may be used to provide the raw material supply of bitumen. The additive to the blended mixture may be made up of emulsions, soaps and latexes e.g. from a liquid concentrate supply known as EPROPACK 2 (Trade Mark of Epro UK Limited) _ The additive components will be selected according to the proportions of "fatty acid" present in the bitumen feedstock, to bring the "fatty acid" propΩrtion to ^" a sufficient level and in combination with a required alkalinity, so that the blended mixture can subsequently be stored in flowable form at ambient temperature.

The blended mixture also desirably has certain suitable fillers incorporated therein according to the type of bitumen used, e.g. bentonite powders of a pack obtainable from Epro UK Limited and sold under the trade name EPRO 1 , and with the unexpected advantage that at least tc sΩme 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 bitumen by conventional techniques e.g. preferably at ambient temperature, and curing immediately on application to form a membrane.

The reason why the introduction of alkaline water into a blended mixture with bitumen has surprisingly beneficial results in rendering the bituminous composition formed thereby to be flowable at ambient temperatures is not clear, and it is not propΩsed to speculate whether it is a chemical and / or a physical phenomenon. The fact remains that this advantage is achieved, provided that the bitumen and the blending water are heated, and the water is at least slightly alkaline.

The ratio of bitumen to water, by weight, is preferably in the range 60:40 to 70:30, with the hardness of the finished product being dependent at least partly upon the water proportion, and also upon any additives introduced into the blended mixture. The hardness therefore depends upon the water proportions, and the presence of latexes, soaps and amount of EPROPACK 2 used (Trade Mark of Epro UK Limited).

A method of formation of a flowable bituminous composition according to the invention will now be described in detail, by way of example only, with reference to the accompanying drawing, which is a flow diagram showing the treatment of a bitumen feedstock tc fΩrrn a blended mixture suitable for subsequent sprayed application to form a membrane on a surface to be treated.

Referring now tΩ the drawing, a method of forming a blended mixture of bitumen and water which is at least slightly alkaline (preferably pH range of 8.5 to 12.5) will

now be described in detail, which is suitable for subsequent application to a surface to be treated by a spray coating technique. The drawing shows schematically the initial treatment of a blended bitumen feedstock, which is preferably a blend of 50 / 200 PEN Venezuelan bitumen (low acidity), which is heated to about 140°C to 150 ^* 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"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 supply comprising heated water from a storage tank 15,- in which the water is heated to about 50 ^β C, and is treated e.g. by EPROPACK 2 (Trade mark of Epro UK Limited) to be at least slightly alkaline, preferably in -the pH range 8.5 to 12.5, and to build-up the proportion of "fatty acids" in the blended mixture if necessary. The drawing is schematic only, and each component of the blended bitumen supply (50 PEN and 200 PEN) may be heated up in its own supply tank and then delivered to blending tank 11.

The blending pump 12 then mixes the raw blend of bitumen feedstock and the blending water, together with fillers and any other necessary ingredients to form a fully blended emulsified product within the blending pump 2, and the blended mixture / emulsion is then discharged via line 16 to a storage tank 17 which holds the blended mixture at an initial temperature maintained of about 95 ^β C. The blended mixture is then fed to storage drums 18 for future use 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 (increasing hardness of the membrane with lowered proportion of water) . It is envisaged that other ratios will

give advantageΩus results, as determined by experiments.

When it is required to apply a sprayed composition to a surface to be treated e.g. the wall of a tunnel, the blended bitumen / water mixture / emulsion is fed from a storage drum to a dispenser pump (not shown) which then pumps the mixture along a first discharge line to a first discharge head from which issues a pumped stream of the mixture.

A second supply cf a dispersing medium e.g. naturally available water treated with an additive, such as EPROLYST 1 or 2 (Trade Mark of Epro UK Limited) to make it slightly acidic, is fed to the dispenser pump via a separate feedline, and is pumped out separately along its own second discharge line to a second discharge head, frcm which issues a pumped stream of this second supply of acidic water.

The additive to render the dispensing water slightly acidic, say in the pH range 2.2 to 4.5 may include calcium salts, such as calcium chloride, and the required acidity will depend upon the alkalinity of the blended bitumen / water mixture or emulsion

The first and second discharge heads are positioned close to each other, and arranged to direct respective streams which converge and meet at a region of impingement at which intimate intermixing, globule to globule, of the respective streams takes place, and a dispersed spray is formed which is applied to the surface which is to be coated and cures immediately. After a period of time, a durable and substantially even bitumen membrane with high flexibility remains firmly adhering to the surface to form a water resistant coating.

It has been found in tests that a flowable bituminous composition can be obtained by the method described above, which can be applied by a spray coating technique at ambient temperature (as compared with existing practice of hot application of asphalt 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.