US2094040A - Method of treating porous surfaces to prevent asphalt adhering thereto - Google Patents

Description

Patented Sept. 28, 1937 I hhi pp;

UNET ATENT FEE METHOD OF TREATING POROUS SURFACES TO PREVENT ASPHALT ADHERING THERE- TO No Drawing. Application December 20, 1934, Serial No. 758,534

6 Claims. (Cl. 134--1) Our invention relates to protective coatings and particularly to asphalt repellent compositions of this character for use in paving.

In constructing a brick road or pavement, for

example, the bricks are laid upon a prepared foundation leaving specified (usually A,") spaces between them which are subsequently filled with hot bituminous material. In this filling operation any excess of material which spreads beyond the joints over the wearing surface of the brick must be removed by scraping after the material has cooled and hardened. Probably due to the fact that the hot bituminous material penetrates slightly into the pores of the brick it adheres very tenaciously thereto and is extremely difficult to remove. Moreover it is impossible in any case to rid the road surface entirely of black stains and streaks caused by the hot bituminous material, and a newly finished road besmeared with such stains presents a very unsightly appearance.

Various means have been employed in an attempt to overcome this difficulty. Among other things, it has been suggested that powdery substances be sprinkled over the brick surface prior to pouring the bituminous material. It has also been suggested that painting the brick surface with whitewash or flour and water would solve the difficulty. The idea in each case being to block up the pores of the brick and thus pour 0 the excess asphalt upon a rather loosely attached paint-like coating rather than upon the brick itself. Such methods have been only partially successful because a large percentage of the excess asphalt fails to come oil in the scraping operation. Then too, where liquid mixtures of the character of white wash or fiour and water are used it is quite impossible on hot, dry or windy days to keep the bricks moist long enough to finish the job at hand.

The general object of our invention is to provide a new type of composition functioning in a novel manner as an asphalt repellent, and which, by proper application at any time previous to the pouring operation, will eliminate the difficulties heretofore encountered. More specifically the object of our invention is to provide a composition of matter of such character that, under the action of heat transmitted thereto by the bituminous material, it will release a gas, thus forming a protecting cushion between the surface of the brick and the asphalt. Such gases as ammonia, carbon dioxide, water vapor, etc., on contacting the hot asphalt expand rapidly and thus cool and harden the lower portion of the asphalt whereby it loses its power to penetrate into the bricks. Another object is to provide a composition of such character that the bituminous material can be readily lifted from the bricks without leaving any discoloration of the surface thereof. A still further object is to provide a composition which is immiscible with asphalt, whereby the excess material removed may be reheated and used again.

We have found, in the case of bricks which present a fairly smooth surface, that spraying or impregnating the surface pores thereof with dilute solutions of organic or inorganic chemical compounds which are either hygroscopic or which, upon drying, retain a high percentage of crystal water, or which release gases like ammonia, carbon dioxide, etc., on being heated up to about the temperature of the molten asphalt, will satisfactorily prevent the asphalt from adhering thereto. Among these compounds are zinc chloride, calcium chloride, alum, Glauber salt, aluminum sulphate, aluminum carbonate, ammonium nitrite, urea, and the sugars, especially the hexoses.

While all of these substances worksatisfactorily, 30 there exists with nearly all of them the possibility of crystallizing. Where crystallization occurs the road surface will take on a salty appearance and the extremely thin coating which should be continuous will frequently crack and open exposing 35 an unprotected surface of the brick which may subsequently be attacked by the hot asphalt. We have found however, that if a moderate quantity of a Water soluble colloid, such as starch swollen in water, gelatin, casein, glue, etc., be incorporated in the mixture it will effectively prevent crystallization.

The following is a typical example of our composition- Water ga1lons 800 Zinc chloride pounds 200 Corn starch pounds 16 In making up this solution the corn starch may be stirred into about 30 gallons of water,

then the entire amount of zinc chloride may be added and the whole agitated until the dissolution heat has swollen the starch. After that, the mixture may be diluted with the remainder of the water. If instead of zinc chloride a salt is used which does not create with water an exothermic reaction, external heat must, of course, be applied to swell the starch.

Another example of our composition is- Water ga1lons 800. Urea pounds 250 Starch pounds 16 When these or similar solutions are applied to bricks, concrete or other porous surfaces, and hot pitch or asphalt is poured 'thereover, it will be found that after partial or complete cooling the bituminous material can be lifted off practically without any effort. An outstanding feature of 7 our invention is that when a brick or other porous surface is coated but once with our composition, hot bitumious material may be poured thereon and removed Without difficulty several times in succession leaving, in each case, a clean and -unmarred surface. This indicates quite definitely that where our composition has penetrated into the pores of the surface and the surface is to all intents and purposes entirely dry, the gas formed upon the application of the hot asphalt provides a perfect protective cushion for the brick.

In the case of bricks, such as the so-called vertical fibre bricks, which present very rough surfaces with deep ridges, curves, rugosities and other irregularities designed to enhance the nonskid characteristics of the pavement, it may be desirable to modify, to some extent, the relative proportions of the several ingredients in our composition so that it may be applied cold in a more or less viscous or paste-like form, or applied warm as a fairly thick liquid which, upon cooling, will solidify to a fairly stiff jelly. Our composition when used in this form fills in the depressions in the surface to which it is applied and prevents the bituminous material from sinking therein. It is to be understood that hot bituminous material will not penetrate into the pores of any surface which has been treated with our composition irrespective of the consistency or viscosity thereof when applied, and that the diificulties encountered with extremely rough surfaces arise from the fact that the material lying loosely in the depressions cannot be removed by the ordinary scraping operation.

The preparation of this more viscous material can be accomplished either by increasing the percentage of the colloid present in the mixture or by reducing the water content, or by both increasing thecolloid and decreasing the water.

Thus, the following formulae may be used to advantage:

Water "gallons" 800 Zinc chloride pounds 200 Corn starch pounds 150 Water gallons 75 Zinc chloride pounds 200 Corn starch pounds 16 Another formula adapted to be applied warm and which forms a jelly-like coating is- Water gallons 120 Zinc chloride pounds 100 Glue pounds 50 Instead of initially forming our composition of such consistency that at ordinary atmospheric temperatures it is a more or less viscous paste or jelly and therefore, in many instances at least, must be heated before it can be conveniently applied by spraying, it is possible, by a very slight modification in the mixing procedure to produce a composition which is sufiiciently fluid at ordinary temperatures to permit spraying but which, under the influence of heat absorbed from the overlying hot asphalt, will expand in volume and form in situ a paste or jelly-like substance.

For example, if 16 pounds of corn starch is stirred into 15 gallons of water and 100 pounds of a hygroscopic salt, such as calcium chloride, is added thereto, the dissolution heat of the latter will swell all of the starch and bring it into solution. If this mixture is now diluted with enough Water to make 50 gallons it will, upon cooling, gelatinize, and must be warmed before it can be applied to a surface.

On the other hand, if only one-half, or 8 pounds, of the starch .content be dissolved by the dissolution heat of the calcium chloride and the other half of the starch be added after the concentrate has been diluted to 50 gallons and cooled, the starch last added will not swell but will remain suspended in the solution, and the viscosity of the composition, at ordinary atmospheric temperatures, will below enough for spraying. However, when hot asphalt is poured over a surface upon which this composition has been sprayed, the starch in suspension will be swollen by the heat from the asphalt and the ultimate compo sition thus formed in place between the asphalt and the underlying surface is a paste or jelly-like substance which fills out all the irregularities in the surface and converts it into one which is temporarily smooth.

Comparative tests of white Wash and our composition :in the form last described above indicate- 1) That in remelting the excess asphalt salvaged from a white-wash-coated brick pavement, the white-wash settled down in a solid cake at the bottom of the heating kettle and clogged up the-outlet pipe, whereas, the small quantity of our composition which adhered to the asphalt rose to the top on reheating and was easily removed as scum;

(2) That where white-wash is used, large quantities of asphalt stick to the scraper so that frequent cleaning thereof is necessary, whereas, our composition acts as a lubricant for the scraper and not only keeps it clean but permits the tool to slide easily between the asphalt and the underlying surface;

(3) That where white-wash is used the finished road is discolored with a streaky white coating, whereas, with our composition the road appears perfectly clean after the removal of the excess asphalt.

In actual practice our composition should be applied so that only the upper brick surface and the upper edge of the sides of the brick are coated. The balance of the sides should be kept as free of the composition as is possible. Where the com position is applied by spraying this may be accomplished by spraying vertically rather than from an angle.

While we have described our invention with particular reference to its application to brick and brick pavements, it is to be understood that our composition may be used in the treatment of porous surfaces generally to prevent the adhesion thereto of hot bituminous material.

What we claim is:

1. That step in the method of treating porous surfaces to prevent molten bituminous material from adhering thereto which comprises applying to such surfaces, prior to the application of the molten material, a water solution of a chemical substance which, upon drying, retains a substantial percentage of water of crystallization; whereby said substance when substantially dry will disengage a gas when heated by the application of said molten material thereto.

2. That step in the method of treating porous surfaces to prevent molten bituminous material from adhering thereto which comprises applying thereto, prior to the application of the molten material, a water solution of a salt which, when heated in a substantially dry condition by the application of said molten material thereto, will disengage a gas.

3. That step in the method of treating porous surfaces to prevent molten bituminous material from adhering thereto which comprises applying thereto, prior to the application of the molten material, a water solution of a water soluble colloid and a salt which, when heated in a substantially dry condition by the application of said molten material thereto, will disengage a gas.

4. That step in the method of treating a porous surface to prevent molten bituminous material from adhering thereto which comprises applying to such surface, prior to the application of said material, a water solution of a chemical substance immiscible with said material and which, when heated in a substantially dry condition to a temperature of the order of said molten material, will disengage a gas; the quantity of said substance present in said solution being sufiicient to produce, when heated by the application of said material to said treated surface, a gas cushion between said surface and said material of such effective thickness and extent as to prevent adhesive contact between the two.

5. That step in the method of treating a porous surface to prevent molten bituminous material from adhering thereto which comprises applying to such surface, prior to the application of said material, a water solution of a hygroscopic substance immiscible with said material and which, when heated in a substantially dry condition to a temperature of the order of said molten material, will disengage a gas; the quantity of said substance present in said solution being sufficient to produce, when heated by the application of said material to said treated surface, a gas cushion between said surface and said material of such effective thickness and extent as to prevent adhesive contact between the two.

6. That step in the method of treating a porous surface to prevent molten bituminous material from adhering thereto which comprises applying to such surface, prior to the application of said material, a water solution of a colloid and a chemical substance immiscible with said material and which, when heated in a substantially dry condition to a temperature of the order of said molten material, will disengage a gas; the quantity of said substance present in said solution being sufficient to produce, when heated by the application of said material to said treated surface, a gas cushion between said surface and said material of such efiective thickness and extent as to prevent adhesive contact between the two.

WERNER E. KLEINICKE. GLOSTER P. HEVENOR.