US2023068A - Bituminous paving mixture - Google Patents

Description

Patented Dec. 3, 1935 UNITED STATES BITUNIINOUS PAVING MXTURE Walter H. Flood, Chicago, Ill.

No Drawing. Application February 26, 1934,

- Serial No. 713,015

7'Olairns. (o1. 106--31)' This invention relates to bituminous paving mixtures adapted to be laid at atmospheric tem-' peratures commonly known as so-called cold-lay bituminous pavements. V

The usual hot mix bituminous paving mixture which is ordinarily laid hot will adhere in large masses when allowed to cool, so that it is impossible to spread it on the street or road at atmospheric temperatures. I

In order to produce a satisfactory bituminous mixture which can be laid cold, it is necessary to provide some means of preventing the individual particles from adhering too strongly to each other in order that it may be easily spread. Another important feature of a'satisfactory cold-lay mixture is that it should remain in a non-adherent condition for an indefinite period before it is used in order that a considerable amount might be placed in a stock pile until it is ready for use.

I am aware that many methods have been used to prevent the particles of the bituminous mixture from adhering too strongly together or setting up, as it is called. Some of these methods are based on the use of a volatile oil, like a naphtha, which softens the bituminous material and afterwards evaporates to some extent when the mixture is compressed into a paving surface.

Some make use of a fluxing oil and a powdered asphalt or tar as the components of the bituminous material, depending upon the gradual fiuxing together to produce the bituminous cement itself.

All of the methods which I know of do not permit the mixture to stock pile for any length of time before it is used. Moreover, the use of a volatile oil such as naphtha or kerosene, or other light petroleum oil, does not produce uniform results, since the amount of evaporation of the oil is largely dependent upon atmospheric conditions. If too much oil remains in the pavement after it is laid, the bituminous material is too soft and the pavement will become displaced and wavy. When a powdered bituminous material is used with a fluxirig oil, the fiuxing action begins as soon as the mixture is completed, and there is no way of controlling it. This action is also dependent upon the atmospheric conditions, being much greater in speed in hot weather than incold.

In my invention I make use of a material which more or less completely surrounds the bituminous coated particles, which does not become-part of the bituminous coating'until the mixture is com'- pressed upon the street or rolled; Uponcom- -the bituminousmaterial by mixing in anysuitable pressing it dissolves in and becomes an integral part of the bituminous coating.

The materials which I use belong to the class of substances known as soaps and may be stearates, oleates, palmitates,- resinates, linoleatesj 5 or other similar salts. I may use the soluble soaps such as sodium, potassium, or ammonium, or the soaps of the metals such as aluminum, zinc, calcium, magnesium, manganese, lead,. or other heavy metal. I prefer the use of aluminum 10 stearate because it is an extremely light powder and thus occupies a large volume of space per unit of weight. I also use magnesium stearate for the same reason; I have found, however, that aluminum stearate does not so readily dissolve 15 in the bituminous material at a relatively high temperature as magnesium stearate.

The choice of thematerial to be added depends upon whether the bituminous mixture is to be laid on the street soon after mixing, or is to be 2b placed in a stock pile for an indefinite period. Another factor which also affects the choice of the material is the weather condition. A bituminous mixture to be laid in cold weather tends to remain in a loose condition much longer than when it is '35 'used in hot weather. a a

' In producing the mixture I take any suitable" aggregate such as'sand or stone, or gravel, or 'a mixture of thesematerials, dry them by any suitable means, and apply the proper amount of bi- 'tuminous material of a grade similar to that in common use in bituminous pavement construction. In order to facilitate thorough coating of the aggregate, I add a small percentageabout one to two per cent-of hydrated lime before mixing with bituminous material. I then may or may not add 'about five'to twenty per cent of a mineral filler such as limestone dust, silica dust, etc., depending upon whether the sand or stone or other aggregate contains sufiicient fine particles to produce 40 the required density and stability. The amount 'of bituminous material depends upon the nature of the aggregate and will vary from about four per cent to eleven per cent, according to the proportions of fine and coarse aggregate present. I use approximately the same amount that is used ,in the ordinaryhot mix paving mixtures. After the aggregate and lime are thoroughly coated with device, I cool the mixture-if it is necessary, by v adding a' small amount of water to bring the temperature tobelow about F. the desired temperature depending uponthe substance to be 'added. In mostpaving plants the aggregate can be dried without heating to an excessively high num stearate or one of the other materials mentioned above. The aluminum, magnesium, zinc, calcium, sodium stearates, or other salts which are brittle, I add in powdered form. The magnesium and aluminum stearates, being extremely light, occupy a large volume of space, so that .a.

relatively small amount by weight is sumcient to keep the bituminous coated particles separated. The temperature at which I add the substance to prevent the particles adhering together-de pends upon how soon the mixture is to be used, on the nature of the mixture, and on the substance used. If the mixture is to be hauled to the street immediately after mixing, a temperature higher than 150 F. may be used; but if the mixture is to be placed in storage for any considerable length of time, the temperature at which the stearate, or similar substance is added, should preferably be around 100 F. When soft bituminous materials are used, the temperature can be much lower, but it is difficult to successfully mix the harder bituminous materials at relatively low temperatures. I prefer to add the soap at as low a temperature at which the bituminous mixture can be mixed and secure a good coating of the particles of aggregate.

Another method which I have found satisfactory is to dissolve the soap in a petroleum oil to make a jelly-like substance. I then add this solution of soap in oil to the bituminous mixture, in place of the soap itself. In this case I use a slightly harder bituminous material in coating the aggregate, so as to allow for the softening action of the oil. In using a solution of the soap in oil I add about two-tenths to three-tenths per cent of this solution compared to the weight of the total bituminous mixture. The amount of soap dissolved in the oil depends upon the kind of soap used and the kind of oil used. For aluminum stearate and paraffine oil I take about twenty parts, by weight, of aluminum stearate and eighty parts of oil and accomplish solution by heating. I am aware that paraffine oil has been used for this purpose, but parafiine oil alone more or less readily mixes with the bituminous coating, Whereas the soap dissolved in the oil retards this action to a very great extent.

I find that I can successfully use the ordinary commercial powered laundry soap, either in its powdered form or dissolved in oil.

One of the advantages of the aluminum, magnesium, calcium and zinc soaps is that they are waterproof, whereas the sodium soap is not. Also, as I have mentioned, the magnesium and aluminum stearates are exceptionally light in weight per unit of volume. When sodium or other soluble soaps are used, the addition of about two per cent of hydrated lime tothe aggregate will produce an insoluble waterproof calcium soap upon reaction with the soluble soap. This reaction will tend to take place gradually and become more rapid when the mixture is compressed, the compression bringing the particles into intimate contact. The amount of soap I use--approxim-ately two-tenths of a per cent of the total weight of the mixture-4s so small that the cost is low, and the effect on the bituminous material isnot in any way harmful. For bituminous mixtures containing coarse particles of aggregate, I find. that onetenth per cent will accomplish satisfactory results. In the ordinary standard sheet asphalt mixtures, containing about ten per cent of asphalt cement, I use about two-tenths per cent of soap, which would be two per cent of the asphalt cement. 5 The soap accomplishes my purpose with a Wide range of bituminous materials, including all that are commonly used in bituminous pavement construction. I have found that it works satisfactorily with hard or soft asphalts, tars and emulsions. 10 One of the distinct advantages is the small amount which is necessary to use. Most of the cold-lay bituminous mixtures employing an oil require that the oil constitutes aproximately ten per cent or more of the bituminous material. This amount 15 of oil impairs the quality of the bituminous material, since the oil possesses no adhesive property, but it is purposely employed on account of its lubricating properties.

Soap is a lubricant and is used in lubricating 20 compounds, ordinary sodium soap, as well as aluminum and other stearates being used for this purpose. However, I use a very small quantity which dissolves in the bituminous material upon compression with the roller or other means com- 25 monly used in street construction. Before compression and while the mixture is still in an uncompacted condition, the soap remains on the surface of the bituminous coated particles and serves as a lubricant, as well as a separating 39 medium to keep the sticky surfaces of the bituminous material apart. I

I am aware that substances such as powdered limestone, magnesium carbonate, Portland cement and other fine mineral powders have been 35 used to prevent the bituminous particles from sticking together, but these are objectionable since they tend to prevent the particles sticking together when compressed on the street. It is most essential that any substance which is used 40 to prevent adhesion of the bituminous coated particles should permit this adhesion to take place when it is rolled on the street.

While I have mentioned sand, gravel and stone as the aggregate which I have used, I do not con- 45 fine myself to these materials, but may use any of the aggregates commonly used in bituminous pavement construction and also organic materials such as sawdust, which may be used in the construction of floors, walks, etc. 50

Having thus described my invention, I claim:

1. The method of making a paving mixture comprising coating a mineral aggregate with bituminous material and adding powdered aluminum stearate to separate the coated particles. 55

2. The method of making a paving mixture comprising mixing mineral aggregate and. hydrated lime, coating same with a bituminous material, and'adding asoap to separate the coated particles. 7 a a 3. The method of making a paving mixture comprising mixing mineral aggregate and hydrated lime, mixing'same with asphalt cement to coat the particles and adding a fatty acid salt to separate thecoated particles. 6

4. The method, of. making abituminous paving .mixture adaptedto bestored and laid cold, commixture-adaptedjto be; stored and laidpold, comprising mixing a graded aggregate with hydrated rate around the individual particles of coated aglime and bituminous cement at a temperature gregate. not exceeding 200 F., mixing therewith a mineral 7. A paving mixture comprising particles of filler, adding water to cool the mixture to less mineral aggregate and hydrated lime coated than 150 F., and adding to the aforementioned with bituminous material, and a coating of a 5 mixture a viscous solution of soap in oil. soap dissolved in petroleum oil around said coated 6. A paving mixture comprising bituminous particles. coated aggregate and powdered aluminum stea- WALTER H. FLOOD.