US1227903A - Process of producing paving material. - Google Patents

Description

NITED STAT S PATENT onrron emronn canssn enYmw, or mass crrr, KANSAS.

PROCESS 0,1 PRODUCING PAJTHI'G MATERIAL.

ltloDrawing.

I ducing paving material from colloidal soils,

and has for its principal object to produce a plastic renewable road surface at a cost low enough to be commercially racticable.

In the accomplishment 0 this object I have sought first to produce a base, or what may be termed mineral a gregate, and then bind it with bitumen'to' cm a paving material, in which is combined the properties of maximum density, minimum poroslty, controllable viscosity or plastic hardness, practical insolubility 'and chemical inert ness, inorder that the material when used as a road surface may avoid, to a great extent, the common defects of permeability,

wavmess, deformation under heat and disintegration by the grinding and disruptive tearing action of wheels.

It has heretofore been recognized that sand aggregates with a filler of dust constitute the closest approach to such a base, hut it has been found impractical for commercial reasons to attempt the fine division of particles requisite for the optimum result by attrition,as the range of plasticity of the paving material having such a base is dependent upon the extreme subdivision of the agthe abolition of pore space, the thinness of speoifloatlen of Letters Patent.

Application filed December 20, 1916. Serial No; 138,138.

pact of iron shod hoofs, and the shearing,

Patented m 29, 1917.

the films, and effective use of binder, to

gether with the consequent water-'proofness and tenacity of the immense surface area of the particles socoated. I am aware that this has been attemptedby the use of grain sizing to reduce porosity. Such processes result, however, in mixtures that retain all the properties of viscous solids, having no defimte shear points, but deforming under stresses and elevation of temperature, displaying but little tenacity and reflecting the character of the binding agent, so that attempts at correction havevbe en along the point lines of the control of the softenin of the bitumen, etc. The thick aspha t films which fill the s aces, or pore openings, in

the comparative y coarse a gregate move in accordance with the laws 0% flowage, that is, the asphalt molecules move on each other, only resisted by the internal friction or viscoslty of the fluid itself, which is entirely independent of the pressure and is a function of the rate of movement or velocity and the temperature. Practically it is obvious that it is impossible to do away with tem-' perature differences in a pavement, and hence changes in the viscosity, and consequently the rate of flow is dependent upon the characteristics of the more fluid phases just stated.

Attempts have also been made to produce such a material by the use of soils, heated and reduced to dust. The same difficulties, however, have been met by the employment of, this process as with the attempts to add fine material, as dust, in the paving material. The process of heating must of necessity coagulate and flocculate the colloidal substances in the soil, so that they do not act as single but as compound particles or aggregates, the surfaces of which are coated so that such aggregates act substantially as coarse sand grams, with the additional disadvantage that such particles are ultimately attacked by water, to the great detriment of the materiaL I particularly disclaim all such methods or uses.

I am also aware that early eflorts were made to produce a paving material by reduction of natural rock asphalts to a magma possibility.

to the'extent of forming a finely divided or colloidal product, hadthe desirability of such a product been known at that time. I make mention of it for the purpose of dlsclaiming any such action or process.

My method base, or mineral aggregate, as distinguished from these heretofore ,mentioned, consists of soil containing colloidal material, and one of the principal steps of the process is to effect such changes in the physical and chemical characteristics of the soil as to increase its inertness or immutability both from chemical agencies and mechanical disintegration, in a, manner to render the use of such a base a commercial Soil which forms the aggregate of the paving material is the variable product. of rock weathering, and it is essential in order to secure uniform results to determine the exact nature, as far as possible, of the soil to be used, especially its colloidal proper-' to a more. dispersive phase or sol condition, wherein the well known phenomena of suspensoids and colloidal solutions, particularly surface energy changes, predominate. I believe, in common with many observers of colloidal phenomena, that this dispersive action is due to the selective adsorption of'ions by the dispersoid from the solution of the deflocculating electrolytes in the dispersive medium, and consider that the tem-- perature and agitation I use greatly increase this action. I use the term adsorption in the sense that it is the action of the particle that induces the film or layer in the dispersive medium immediately'surrounding it to become more dense, and chemically removed from its'surface.

electrostatic repulsion and attractlons seems active-than that portion of the liquid more best to accord with the actions I have. ob-

- served, viz., dispersion of the finer particles,

' ume. of water.

more complete separation of .the coarser from the finer particles, and greatly increased mobility and ability to retain the aggregate in suspension, with a 'ven vol- The dispersion o the particles allows complete coatin with fluid bitumen, the increased mobility allows a reduction of water in the composition, which results' in economy both of initial heating The theory of and drying, and in addition permits the use of less expenditure of energy for mixing and pumping.

Deterioration of an asphaltic pavement is caused to a large degree by chemical action, which practically is always dependent upon the presence of water. The exclusion of water is then of vital importance to the continued .high quality of a pavement.

I accomplish this desirable result by my method of, incorporation of the bitumen.

Not only do I, in contradistinction to any known process heretofore disclosed, utilize the advantage of existing colloidality, but I Induce dispersion to the maximumdegree, by the combined purposeful action of heat, agitation and chemical and electrostatic action, wherein the surface tension of the dis persive medium is lowered and the selective adsorption of the required ions encouraged to. bring about the electrostatic repulsion which manifests itself in the phenomena of the maximum disperse phase.

I can consider then that each particle is separated by an intervening liquid phase,

and that this phase is of lowered surface tension and that positive repulsion probably exists between the dispersed particles in varying degree by reason'of the selective adsorption of 1011s from the added defioccu- "lat'ing electrolytes, and furthermore that complete defiocculation does not exist unless this condition or its equivalent is brought about by the proper concentration and quantity of the added reagent.

When bitumen is added to such a properly treated dispersoid and suspensoid, each particle is enveloped in a thin film covering the adsorbed water film on the particle. Between the particles so coated is a continuous, dispersive medium -that is capillary and free Water. When this is. removed by vaporization or the application of heat, it is evident that the bitumen 1s in situ, andis under no necessity, as in other processes, of being rendered thin enough, that is of'having its viscosity reduced by heat, to facilitate its introduction into the minute voids and capillary and sub-capillary pore spaces that existin such a fine aggregate.

It is clear that before the removal of the water the solid particles and the bitumen constitute two separate discontinuous phases dispersed in the free or pore water of the aggregate, and that it is only upon heating that the bitumen becomes the cementitious agent acting as the dispersive medium.

This transition stage is of great practical importance, as it allows the material to be made and stored, and when handled on the street does not require the heating and haildling of heated bitumens.

The process of 'manufacture is much simpler and less equipment investment and bitumen.

sible where the whole process must be carried out at the time of laying.

This economy and utility is especially marked in the maintenance and repair of street surfaces, as the equipment is extremely simple, the material having only to be heated to expel the residual water and to cause the fluxing and subsequent hardening of the Then We have a compound of practically two continuous phases, reflecting the nature of the more solid phase for the reason that the surface area is so great, the points of contact so numerous, and the films of bitumen so extremely thin and consequently rigid that .at normal temperature no flowage is exhibited, but. only slippage of the more solid particles under stress, a property best described by the term plastic hardness.

The routine procedure in preparing pav-- ing material in accordance with my process is as follows:

I take a soil, for examplea loess or clayey soil of glacial origin, and classify it by elutriation, using only three separations, sand, silt and clay, anything smaller than .005 millimeters being classified as clay, siltmaterial anything that will pass through'a 200 mesh screen and larger than .005 mm., and sand anything held on a 200 mesh, this division being purely arbitrary and one I have found convenient. The measurement of the finer material is effected with a microscope and the aid of 'a hemoglobinometer such as is commonly used for blood counts.

After determining the proportions of each division by dry weight I take weighed quantities thereof and add about ten times the volume of water (the water I expect to use) and place in long test tubes which are subj ected to violent and continued agitation. I then add trial quantities of an appropriate electrolyte, for example sodium carbonate in solution, using one or more tubes for control tubes, and observe the rate and character of the resultant suspension. Practically the most completely dispersed suspension willform the most mobile and the least viscous mixture and will combine to the greatest degree of perfection with the bitumen at the proper temperature. while the amount of reagent required to be added is subject to measurement by weight or volume, the controlling feature of quantity so used in a given case seems to be the extent to which the adsorptive process takes place, which is in turn subglect to many variables, surface extent of t e dispersed particles, temperature, and time o agitation.

. so I calculate the minimum amount of reagent It is understood that required from the weight of the soil when commencing a trial. An excess of reagent amount is sometimes in excess when the heat and stirring is too long continued. Sodium silicate and sodium hydrate are sometimes more effective than sodium carbonate, and the chemical constituents in the cla also determine the kind and quantity of ectrolyte used. Calcium hydrate and other calcium compounds particularly affect the amounts must be avoided and what appears the right 7 of sodium carbonate added. Roughly one pound of 58 I carbonate to the ton of loess has proven efiective. The temperature of the mixture should be from 185 to 210 degrees Fahrenheit; the water content should not exceed 46 per cent.; the bitumen should be heated to at least 300 Fahrenheit, and, of course, varying with the bitumen used, the minimum viscosity being desirable without danger of over-heating.

After deflocculation bitumen is added to the base by gradual injection into the heated mass through a centrifugal pump and completely circulated until uniformly mixed. The material is then pumped out and allowed to air dry until required for use in laying a road surface.

When required for use on a road, the material is heated to flux the mass and laid on the road base to form a surface having the properties hereinbefore mentioned.

Having thus described my invention what I claim as new therein-and desire to secure by Letters-Patent, is: I

1. The process of producing paving material consisting in stirring soil containing colloidal material with a 'deflocculating reagent and water to deflocculate the soil, heating the deflocculated mass, adding fluid bitumen to the latter and drying the resultant product. 1

2. The process of producing paving ma- I per cent: commercial sodium ing the deflocculated mass, adding fluid bitumen to the mass to coat the individual soil particles, drying the mass, and reheating the mass to flux the material.

3. The process of producing paving material consistin in stirrin soil containing colloidal material with a eflocculat' reagent and water to deflocculate the soil, eating the deflocculated mass, adding fluid bi-.

tumen to the latter, air drying the resultant product and reheating the latter to flux the materia In testimon whereof I afiix my s' ature. GUIIYFORD CRESSE GL %.TN.