US2323435A - Method of preserving quicklime - Google Patents

Description

Patented July 6, 1943 UNITED STATES PATENT OFFICE METHOD OF PRESERVIN G QUICKLIME Nathan Wiseblood, Malden, Mass.

No Drawing. Application May 23, 1940, Serial No. 336,743

3 Claims." (01. 23186) Pavements having non-skid characteristics have been produced heretofore using road materials composed principally of coarse aggregate and containing a very small amount of fine aggregate. Such roads contained large voids which accounted for its anti-skid characteristics. Because of the presence of a large proportion of coarse aggregates, the surface area of the aggre-' gate was small. As a result the amount of bituminous bond which could be used was limited. Lack of fine aggregate causes considerable segregation in the mixing, hauling and spreading of these pavement mixtures. If too much bitumen is used, the bitumen runs off the stone in handling and will produce fat spots in the pavement. The stability and durability of such roads was not great because the road was extremely porous and, consequently, was penetrated by air and water causing oxidation of the bond and disintegration of the road.

It is an object of the present invention to provide a road structure which is stable and durable and has an anti-skid surface.

Prior to the present invention, it has not been possible to use materials in road building which contain clay and loam. The clay prevented the adherence of the bitumen to the aggregate and the presence of organic matter in loam prevented the bitumen from becoming hard. Because of the lack of care in stripping the surface at stone quarries, clay and loam are present in the stone.

acidity prevents the adherence of asphalt and there is always danger of stripping because of the hydrophilic properties of gravel.

It is another object of the invention to provide a road structure and method of making the same utilizing such waste materials.

It is another object of the invention to provide a method of making a cold laid pavement which may be opened to trafiic within twenty-four hours after being finished.

It is another object of the invention to provide a pavement mixture which can be made up ready for use and stored in bales until needed.

-It is another object of the invention to provide a method of making a pavement without previously drying the aggregate.

It is a further object of the invention to prolarge quantities, Gravel also seldom has been used because its vide a method of making a cold laid pavement using a hard asphalt having a higher penetration and a lower softening point than hasflheretofore been possible.

A further object of the invention is to provide a method of manufacturing, storing and using quick lime in a finely divided state.

In general, a road made in accordance with the invention comprises a dense foundation and a surface course of fine texture having 15 to 25 per cent voids to provide anti-skid characteristics. Preferably, the foundation comprises a base course and a top course. In forming thebase and top courses, the basic road materials, such as aggregate, are graded and mixed with 5 to 15% of a cement formed by pulverizing hard asphalt with quicklime. A flux, such as an asphaltic oil or other soft asphalt, is added and the uniform mixture is spread and compacted. Before spreading the top course upon the base course, a light mineral oil, such as naphtha or kerosene, is sprayed over the base course to facilitate amalgamation of the hard and soft asphalt and to assure a good bond between the two courses. Similarly, before spreading the surface course upon the top course", alight mineral oil is sprayed upon the top course.

In forming the surface course, basic road materials are graded and mixed with lime and, when the mixture becomes warm, a light mineral oil is added. Hot asphalt cement is added and the mixing continued. The surface and top courses, preferably, are compacted together so that the former is made an integral part of the latter. The basic road materials used in the surface course are graded intermediate sizes containing no coarse aggregate and no substantial amount of fines, providing a surface having from 15. to 25 per cent voids.

The invention contemplates the use of aggregates found at or near the place of road construction and which may contain clay or loam. For the baseand top courses, these materials may be mixed either with washings of washed stone screenings or washings of sand and gravel. For the non-skid surface course, washed stone screenings or concrete sand, that is, washed graded sand, may be used.

The cement made by pulverizing lime and hard asphalt can be stored in bags, barrels or bulk and used as needed. Preferably, this cement is pulverized so that at least 95% passes a No. 20 mesh sieve and at least 50% passes a No. mesh sieve. The asphalt protects the lime from the action of carbon dioxide in the air. This-cement may contain from 25 to 75% lime and the remainder asphalt but, preferably, contains about '70 per cent lime and 30 per cent asphalt. When pulverized with lime, a hard asphalt having a penetration as high as 30 and a softening point as low as 175 F. may be used. Otherwise, it would be necessary to use an asphalt having a penetration of less than 10 and a softening point greater than 200 F.

The use of lime as described dries and heats the wet aggregates and neutralizes acid mate" rials present. It makes possible the use of aggregates containing clay, gravel, loam and other materials having hydrophilic properties. The hydrated lime, which results in the chemical action of the quick lime with the mixture in the aggregates performs an electro-chemical as well as a mechanical function by tending to provide the entire mineral mixture with properties producing a stronger bond with the binder. The lime produces a mortar due to the crystallization ofcalcium carbonate. Th more finely divided the quick lime, the greater is the speed of action in drying the wet aggregates and the greater will be the heat generated due to the chemical action and the smaller will be the amount of lime required to perform the necessary work. This is true if the quick lime has not been affected by air in being pulverized. It has been found that by pulverizing quick lime together with hard asphalts that the asphalt prevents the action of air and protects the quick lime from weathering in the handling, shipping and storing in bags, barrels or bulk for several months. The lime prevents crystallization of the asphalts and the loss of elasticity. It also hardens and toughens the asphalts and permits the use of more flux and softer asphalt. Consequently, the pavement will not become soft in hot weather nor brittle in cold weather; The presence of the lime speeds up the amalgamation of the hard and soft asphalt.

In the preferred practice of the invention, the grading of the aggregates in the base, top and surface courses should fall within the limits in dicated in. the following table when tested by standard U, S. Tyler square opening sieves. The figures in parentheses in the table indicate the preferred amounts Sieve Base course Top course Surface course Per Per Pass- Be- M mg tamed 111353; 111. ax. in. llax.

%/I 0 0 lg 15 (25) 45 20 (30) 50 38!! MI! 0 5 2 (5) 10 (1o) 40 10 (35) 45 #10 (30) 60 3O (30) 50 #10 #30 (40) 60 #50 5 (15) 25 #50' l0 (15) 15 (20) 35 0 (10) 20 #200 2 5) l0 5 (l0) l5 In the preparation of secondary roads and base courses by road mixing, the material in the subgrade should be tested and the amounts of tested blending materials, which may be crushed stone screenings, screened gravel, washings of screenings and sand, bank gravel and sand, should be determined so that the aggregates for the base cours and secondary roads will fall within the allowed graded limits. If the material of the subgrade is suitable for the top course, the required amount is gradedto the shoulders of the road,

and left in windrows where later it can be used in preparing the top course. The required amount of blending materials should be uniformly spread over the sub-grade and mixed with the materials of the sub-grade to produce the desired thickness of the base course or the secondary road, which should be between 2 to 4". About 5 to 10% by weight of a cement comprising a mixture of lime-and hard asphalt is then spread over the aggregate. The materials are then mixed by means of harrows or motor graders or other various types of road mixing equipment. A soft asphalt or asphaltic oil then is sprayed over the mixture as a flux. Preferably, a 65% asphaltic oil, that is, one containing about 65% of asphalt having a penetration, is used as a fluxin an amount between to /2 gallon per square yard per inch of thickness of pavement. Mixing is continued until the materials are thoroughly mixed. While the base course or secondary road is being compacted, a light mineral oil such as naphtha or kerosene in an amount from 0.02 to 0.05 gallon per square yard should be sprayed upon its surface to ensure rapid amalgamation of the hard and soft bitumen. The materials should be thoroughly compacted to secure a maximum density.

' The materials for the top course may be mixed in a pug or concrete mixer. The required amounts of blending materials are spread uniformly over the materials from the subgrade that previously have been graded to the shoulders of the road. This material is placed in the mixer together with between 6 to 12% by weight of lime-asphalt cement and agitated until the moisture either has combined with the lime or has been driven oil by the heat generated. From 3.5% to 6% by weight of the total mixture of a 65% asphaltic oil then is added and thoroughly mixed in. A light mineral oil then is sprayed upon the surface of the base course and the mixture for the top course is spread thereupon to provide a top course about 1 to 3 thick. The light mineral oil increases amalgamation of the top mixture near the base course and also ensures a good bond between the base and top courses.

The road material used in the surface course, preferably, is washed stone screenings. Concrete sand, that is, washed graded sand, may be used if stone screenings are not available. This material is placed in a twin pug mixer and from 2 /2 to l of quicklime added. When the aggregate is dry and warm about 0.5 to 1.5 per cent of naphtha or light kerosene is sprayed in the mixer. When the surface of the aggregrate is fully coated from 6 to 9% of hot asphalt cement having a penetration between 60 to is poured into the mixer at a temperature between 240 F. and 340 F.

The surface and top course mixtures, preferably, are spread and compacted at the same time. After spreading the top course mixture over the base course, a light mineral oil, such as naphtha, is sprayed upon the top course in an amount from 0.02 to 0.05 gallon per square yard and rolled lightly. The surface course mixture then is spread over the top course in an amount between 30 to 80 pounds per square yard. The top and surface courses are then compacted thoroughly as one course. By rolling the two courses together the surface course is so impregnated into the top course that the thickness of the surface course can be as little as /4" without danger of stripping and ravelling. Thesurface course will contain between 15 to 25% voids. Inasmuch as the thickness of the surface course is small and the voids large, the naphtha evaporates readily and the pavement may be opened to traific within twenty-four hours.

A road constructed in accordance with the invention is stable and durable because the foundation is dense and resists penetration by water and air. Consequently, there is little possibility of disintegration due to oxidation. The foundation contains a relatively large proportion of fine aggregate and, consequently, has a large surface area coated with bitumen. As a result the road contains a large proportion of bitumen giving a strong bond without segregation and resists ravelling or stripping. The cost is greatly reduced by making use of materials at the place of construction as well as washings which previously have been discarded as waste. The surface, which contains a large proportion of voids to provide anti-skid characteristics, is relatively thin and is formed as an integral part of the foundation.

I claim:

1. The method of preserving quicklime in finely divided form so that it will remain active when stored which comprises pulverizing the quicklime with from to per cent of hard asphalt.

2. The method of preserving quicklime in finely divided form so that it will remain active when stored which comprises pulverizing the quicklime with from 25 to '15 per cent of hard asphalt, so that at least 95 per cent of the powdered material will pass a No. 20 mesh sieve.

3. The method of preserving quicklime in finely divided form so that it will remain active when stored which comprises pulverizing the quicklime with from 25 to 75 per cent of hard asphalt, so that at least 95 per cent of the powdered material will pass a No. 20 mesh sieve and at least 50 per cent of the powdered material will pass a No. mesh sieve.

NATHAN WISEBLOOD.