US 2308289 A
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atented Jan. 12, 1943 NITD WINTER ROAD SAND James E. Lawrence, Beverly, Mass.
Application August 20, 1940,
Serial No. 353,381
The winter sanding of highways and the like has come to be a very considerable public problem. As is well known, this sanding of icy highways runs into the expenditure of many hundreds of thousands of dollars in single States. Even with large and generous appropriations to spend on these winter projects, certain difiiculties seemed inherent or so apparently insuperable as to baffle the best of road engineers and experts.
One of the great troubles in winter sanding has been the loss of sand, cinders, or equivalent anti-skid abrasive material on wind-swept stretches with the necessity of re-sanding at new expense and consequent delay in making the equipment available for other jobs.
Another dificulty lay in damage to equipment when the sand caked or lumped and clogged the spreaders, causing breakage of gears, drive chains and other parts of these machines.
Solution of the problem was attempted from various viewpoints and one of the most promising seemed to be in getting some kind of a mixture that would disintegrate an icy surface and so gain a hold against wind dislodgement. Such proposed mixtures were expensive and hard to handle successfully.
The use of rock or like coarse salt (NaCl) on frozen places has been most common practice about walks or in frozen switches of the tracks of railroads or trolleys. It was effective to melt ice, except in very low temperatures, but as it is only capable of relatively low brine concentrations in field work freezing temperatures approaching 6 F. had to be watched very carefully.
For the laying of dust, calcium chloride (CaClz) came early into use in modern road treatment especially on dirt or gravel roads where sprinkling with water was impracticable for lack of convenient hydrant or like supply and where tank wagons with spray bars were not available as part of small town equipment.
With the advent of the hard surfaced high ways of bituminous, but more particularly in the case of roads of cement mixtures, great difficulty was experienced because they iced or became slippery with high skidding danger to automobiles and like fast moving traffic. Treatments of various kinds with calcium chloride (CaClz) were tried and with some success. Two major dithculties were encountered. The calcium salt while highly hygroscopic was expensive for ordinary known methods of handling. Also, it did not hold the sand or like abrasive to the road surface and so was blown or swept off by wind or tire velocities.
The cost of sand suitable for use on such surfaces was and is very high. Even under careful management the abrasive bill was a very large factor, running into hundreds of thousands of dollars in States with modern highways, so that the burden fell heavily on the local taxpayer. The sand generally went Where it was not intended to go by drift to abutting property and thereby entailed a factor of such high percentage of waste that every effort was made to check it.
The patent art early reflects the serious efforts to combat the increasing menace to life as the number of vehicles increased and speed capacity developed. The use of sand mixed with limestone or cement, or with salt and calcium chloride as a component of the surfacing material of pavements is indicated to prevent the accumulation or formation of ice on a pavement.
As motorized plowing and scraping on main highways became more common, the menace of the ice film increased. Still the thought seems to have been to melt or prevent the formation of such ice films or coatings.
Common salt and calcium chloride in granulated, flaked or powdered form were tried in mixtures with lampblack, powdered charcoal, coal or coke dust. Ferrous oxides and ores were also tried in the effort to add heat absorption to the mixture applied to the road surface.
In an efiort to anchor the sand to the ice, combination treatments were tried by which different mixtures were fed from a rapidly moving truck using two or more screw feeding hoppers for the spreader disc by which fine, low moisture sand and dehydrated calcium chloride to absorb the water of the sand were applied to the road surface.
My present invention contemplates the application of ordinary sand or other abrasive material to the road with a previous inexpensive processing, so that the sand becomes a novel material or state of material condition by which it has all of its old advantages without being subject to previous disadvantages.
According to my invention or discovery, I work from what might be called a quicksand basis. In nature quicksands are kept living or in a state of free motion by spring action from below by which water and air bubbles keep it in a state of suspension.
In my basis of winter highway engineering I have my sand treated at time of loading or treated and stored in bins or stacks convenient to the project. This I apply to the highway in a state of saturation of the sand by a calcium chloride brine.
It has been heretofore noted that the calcium salt on account of its high hygroscopic character was dangerous to use on cement or like surfaced ways. ts activity on surface pores was so great as to start disintegration of the hard cement itself.
According to my concept I use the calcium salt but in greatly reduced quantities and find it actually more economical on account of higher efficiencies according to my invention. This is due to the basis of the salt as efliciently applied and also to the very high sand economy I have been able to effect and a consequent reduction in cement surface.
A comparison of calcium chloride and rock salt solutions for ice control purposes shows the following:
Flake calcium chloride readily dissolves in either warm or cold water, while rock salt dissolves slowly, even with constant agitation, especially in cold water. On a standard rate of solubility test in water at 30 C. (86 F.) with mechanical agitation at the rate of 40 R. P. M. calcium chloride dissolved in 9 the time required to dissolve rock salt in equal concentrations (20.25%) using respectively 2.92 lbs. calcium chloride per gallon of water and 2.18 lbs. of rock salt per gallon of water. With agitation at 68 R. P. M, and other factors as above, the calcium chloride dissolved in A; the time required for rock salt. No tests have been made in colder water, but flake calcium chloride undoubtedly would show even more favorable solubility rates as compared with rock salt. Even under these very favorable conditions, thirty-five minutes were required for complete solution of the rock salt.
A solution containing 5 lbs. of calcium chloride per gallon of water has a freezing point of minus 60 F. The lowest freezing point obtainable with a sodium chloride solution is minus 6 F. This solution must have a concentration of 23.3% NaCl equivalent to 2.6 lbs. of rock salt per gallon of water. Deviation either way from this concentration raises the freezing point considerably. A solution containing 2 lbs. of rock salt per gallon of water has a freezing point of plus 5 F. Due to the fact that it is impossible to maintain concentrations within close limits in the field, it would seem that the lowest temperature at which rock salt solutions could be safely used would be about +5 F. Air temperatures below this may be expected at times during most of the ice control season. In view of the fact that freezing of the solution in the tank, pipe lines, flexible hose and nozzle would completely disrupt the solution method of treatment, we believe that the use of a calcium chloride solution which will not freeze at any winter temperature is essential.
Reports indicate that the sand used for ice control in the Commonwealth of Massachusetts has an original moisture content between 2 /,2% and 3 /2%. A moisture content of 3% is equivalent to approximately 75 lbs. or 9 gallons of water per cubic yard of sand. If too much water or solution is added to this sand it becomes saturated and any excess will drip out. The test indicates that'only 6 /2 to 8 gallons of solution per cubic yard of sand can be added advantageously. This gives a total water content of approximately 15 to 17 gallons of water in a cubic yard of the wet or treated sand. The addition of 6 to 8 gallons of rock salt solution can incorporate only about 15 lbs. of commercial rock salt per cubic yard of sand. This quantity is insufficient for adequate stockpile protection. The use of calcium chloride solution in the above volumes (6 to 8 gallons) will permit a maximum treatment, on the basis of flake calcium chloride, of about 32 lbs. per cubic yard of sand.
Another factor which might be considered in com aring the two products for the solution livery to the tanks.
method of treatment concerns the exothermic action of flaked calcium chloride and the endothermic action of rock salt. When dissolving the flake in water a very noticeable rise in the temperature of the solution is noted. This heat is held by the solution for a considerable period of time, and is advantageous in treating sand or thawing frozen stockpiles. Sodium chloride on the other hand produces a slight lowering of temperature when dissolved in water.
Multiple compartment tanks are inconvenient if it is desired to dissolve the calcium chloride directly in the tank. It is therefore advisable to use single compartment tanks or remove the partitions if such tanks are to be used permanently.
Whenever possible mechanical loaders should be used for loading the sand trucks, except in the case of elevated bins which eliminate this loading cost. The spray nozzle should be mounted just underneath the loading chute to spray the sand as it falls into the truck.
Instead of pre-treating the sand at the pit, it
may be preferred to stockpile untreated sand and then treat with calcium chloride solution a section of the pile sufiicient to provide workable material for each succeeding storm. Experience indicates that frozen stockpiles can be readily thawed with calcium chloride solution. When treated in the afternoon with solution, frozen stockpiles were entirely free and workable the following morning. seems preferable for general use.
Flake calcium chloride can be readily dissolved either in the tanks or in 50 gallon drums for de- The calcium chloride should be added to the water (rather than adding water to the calcium chloride) and will dissolve readily with a little agitation by air, mechanical or hand stirring. A still simpler method is to use a fine mesh wire basket hooked over the edge of the drum or tank so that it is partially immersed in the water. Flake calcium chloride placed in this basket readily dissolves without the aid of agitation, except a little stirring after dissolving to insure uniform concentration.
Water for making up the calcium chloride solution may be available in a few cases at the tank location. However, in many cases the water supply may be at some distance and it will be necessary to truck either the water or the prepared calcium chloride solution to the storage tank. A tank truck or drums on a truck can be used for this purpose, preferably the former. In some cases a central plant may be desirable where the solution can be made up and then trucked to various storage tanks.
My sands are extremely free flowing, as has always been attempted but never really attained. I have at times used the expression quick or fast as any sand treated according to my invention will not cake or clog.
According to my method of sanding the abrasive is preferably as moist as possible without actually dripping. My brines so permeate the sand as to wet or film each particle. They are of such predetermined strength or concentration, according to weather conditions or prevalent temperatures, as to avoid freezing without being wasteful.
I have discovered and proven by careful tests the reasonable limits within which my invention operates smoothly and with high efficiency to produce novel results long sought but never attained. By it I have effected impressive savings in the amount of calcium chloride used and in the cost However, pre-treatment of this factor, while maintaining maximum efficiency.
By using lesser amounts of my active salt the damage to concrete roads (by pore penetration and subsequent freezings and thawings to degenerate the surface skin) is reduced to what is really a negligible item.
In action my treated sands make instantaneous attachment (as compared with four or five minutes attaching time as formerly) of the discrete grains to icy surfaces with no loss of wind-swept stretches so that re-sanding is not necessary. On account of its great freedom of internal movement between particles, distribution is uniform and sand costs of given sections of ways are cut. Where ways are free of ice my sands hold moisture, stay damp and adherent and avoid the former dangers and discomfort to travelers from wind driven particles which had not been frozen down.
I have not attempted illustration of equipment as my invention is fortunately capable of practice with present available mechanical appliances. I advocate the construction of bins and tanks or better adaptation of present devices now on hand.
My methods can be practiced with makeshift equipment but it has as one of its fundamentals a basis of prompt handlings and continuity of work movement that makes for maximum efliciency which is so essential to what is often emergency work as well as the routine of lesser extremities.
For best results I prefer bins for my treated sands and. tanks for my brines, but temporary stockpile storage may also be used. According to my invention I may use between 6 and 8 gallons of solutions per cubic yard of sand, depending somewhat upon the gradation of the sand and its original moisture content. The treated sand, for maximum effectiveness, should be as moist as possible without dripping.
The tests indicate that a solution containing 4 pounds of flake calcium chloride per gallon of water will be satisfactory under all ordinary Winter conditions. This is equivalent to 3.4 lbs. of flake calcium chloride per gallon of solution. The concentration of the calcium chloride solu tion can be increased, if desired, to 5 pounds of flake calcium chloride per gallon of water (equivalent to 4 pounds of flake per gallon of solution), but should not exceed this quantity.
For fall and spring use the concentration can be reduced if desired. The following table shows the concentration which can be safely used down to the temperature indicated.
Pounds of flake calcium chloride Temperature Per gallon of water Per gallon of solution Reports of work carried out in accordance with my orders issued in the maintenance of public highways in winter months with such satisfactory results that I have used herein abstracts relating to the treatment of abrasives as practiced according to my invention. While I have found the calcium as compared with the sodium chloride far more eflicient and economical in public service use, it seems advisable for the understanding of my invention that I compare the two. This is not to be understood as by way of limitation, but for instruction as to the results of my concept, use and such research as I have had time to have made or receive. 7
As a more complete table of data showing the use of brines of predetermined concentration for different temperatures I quote the following taken from practical tests and calculations on winter sanding:
Lbs. -80% flake Gallons Gallons calcium chloride filnal water Temperature vo ume required at which Specific g i g crystallizagravity 6 ion a Per Per 0 (column (column w g gallon of gallon of 60/60 2) is added 3) to water solution to I produce 1 gallon 01 gallon of water solution 0.27 0.27 1.022 1.012 .988 0. 91 0. 87 1. 066 l. 041 962 1. 45 1.36 1. 102 1. 066 939 1. 87 1. 72 1. 128 1. 086 922 2. 23 2. 0? 1. 149 1. 103 907 2. 56 2. 29 1. 168 1. 120 893 2. 2. 51 1. 184 132 883 3. 14 2. 73 l. 198 1. 150 871 3. 39 2. 93 1. 212 1. 162 .861 3. 64 3. 10 1.224 1.172 .852 3. 88 3. 28 1. 237 1. 186 844 4.14 3. 45 1. 248 1. 200 834 30 4. 39 3. 60 1. 258 1. 212 826 35 4. 57 3. 74 l. 266 l. 223 818 4. 74 3.85 1.275 1. 231 .813 4.87 3. 94 1. 280 1. 238 808 4. 3. 98 1. 283 1. 242 816 5. 03 4. ()3 l. 287 l 246 804 5. 10 4.08 1. 290 l 250 801.
By observing the temperatures and concentrations indicated in this table highly satisfactory results will be attained and very considerable economies effected.
What I therefore claim and desire to secure by Letters Patent is:
l. A winter road sand consisting of discrete free-flowing grains having a wet adherent film of predetermined unsaturated brine concentration of calcium chloride on the surface of the grains, whereby the grains become embedded in surface ice pits at the area of film contact with an ice surface on which the sand is spread.
2. A winter road sand as in claim 1, in which there is six and one-half to eight gallons of brine per cubic yard of abrasive, and the brine is at a strength of between .27 and 5.10 pounds of calcium chloride per gallon of water.
JAMES E. LAWRENCE.