STRIPPING TESTS TO DETERMINE THE QUALITY OF AGGREGATES

Stripping Tests to Determine Quality of Aggregates and Bituminous Material to be Used in Bituminous Construction

FROM time to time there creeps into the work of the Materials Engineer new terms and new fields of endeavor. The rise of the use of large amounts of bituminous material with all classes of aggregates has brought to the fore noticeable differences in their behavior. Not only is the behavior different with the same oil and different aggregates, but it is also different with the same aggregate and different oils. Thus we have been forced to cast a wandering eye upon the phenomenon which has been termed stripping.

Stripping of asphalt films apparently has been known for a long time, but what it means or how serious it is, is a ques tion that has not been fully answered. I do not presume that I can answer it here. I will, however, offer a definition. Stripping is the inability to maintain around a mineral particle a continuous film of bituminous material in the presence of water. This inability to maintain a continuous film may be due either to chemical or physical repelling effects of either one or both of the materials used.

There are several test methods that can be used to exhibit the inability of an asphalt after application to adhere to a mineral aggregate. They are as follows:

Each of these tests exhibits in its way the inability of an asphalt to adhere strongly to the mineral constituents to which it is applied. And now for a discussion of each of these tests.

1. The swell test.

The swell test is one method for determining the adhesion existing between a granular material and the applied asphaltic material. In a paper prepared for the Montana Bituminous Conference by the writer and W. W. O'Harra, Chem ist in the Arizona Highway Department, it was definitely shown that the type of oil, its processing and other characteristics (Xylene equivalent) had a great influence on the resulting swell. It was also shown that length of time of exposure to water had a very definite effect on the swell. All tests in this paper were made with SC-2 oil, but it can be assumed that heavier oils would exhibit somewhat the same tendencies. The swell test can be used either on the total ag gregate or on a portion of it. It is only necessary to determine the proper limits for each determination. At the present time the general consensus of opinion rates it as the best method available for determining the properties of a granular material when mixed with bituminous material.

The water asphalt preferential test.

Recent tests in the laboratory of the Arizona Highway Department indicate that the water asphalt preferential test is both a function of the oil as well as a function of the curing time of the oil aggregate mixture before application of the agent (water). The relationship between the oil and the resulting stripping action is not nearly so well defined as in the swell test. Dr. Hans F. Winterkorn,

By JULIAN W. POWERS

Engineer of Materials ARIZONA HIGHWAY DEPT.

(A paper delivered at the Dallas Convention, American Association of Highway Officials) In a paper prepared for this year's (1938) Montana National Bituminous Conference says: "The only definite conclusion to be derived from the use of the water-asphalt preferential test is, that mineral which goes to the oil phase is a good material, but a mineral which does not do so is not necessarily bad. To reject materials on the basis of such a test is liable to become an expensive sport."

We concur in this statement as the test is now made, but future relations based on a more adequate study and a longer time exposure of the bituminous material to the aggregate allowing possible orientation of the asphalt may result in a better correlation to actual field results. This test is applicable only to the minus No. 200 sieve material.

The stripping test, as outlined by the B. P. R.

In this case bituminous material to be used on the project is the oil to be used in the test. A curing period is allowed after which the mixture is agitated with water for a fifteen-minute period, and the results estimated and reported as no stripping, slight stripping, and a bad stripping. The results are not easy to estimate and are influenced appreciably by the temperature of the liquid. In order to get a more precise method of estimating the stripping we have used mixtures of methanol and water. Methanol itself does not tend to strip any of the materials we have used with it to date. This method holds some promise as it will show in most cases a definite point at which materials will, or will not strip. In the high ranges of methanol concentration there is a slight solution of the asphalt by the methanol which may cause errors in the test procedure in that range. This percentage is in the neighborhood of 90% methanol and 10% water. It is probable in this range that materials will not be suitable and this need not be a concern.

In order to test the effectiveness of this method to differentiate between materials we selected several uniform materials, crushed, screened, and washed them, and added SC-6 road oil. The mixes were then cured and agitated as called for by the Bureau of Pubile Roads with both water and water methanol solutions of varying proportions. The results of these tests on uniform materials are as follows:

8. Gneiss (Pegmatitic) 85 9. Silicified Limestone 0 (Shows some slight stripping up to 25% methanol) Of these materials, chert, basalt, and mixtures of basalt porphyry and arkose have been used on work in this State with nearly all classes of oil. So far as can be determined the roads are fairly satisfactory. It might be noted, however, that those constucted with chert aggregates do exhibit some stripping as evidenced by return of the surface to the natural color in a very short time. Until more data is accumulated by this method, or methods patterned after it, using possibly other miscible agents with water, and the ultimate correlation of such methods, no limits should be set for satisfactory aggregates.

There has been a good deal of effort put forth by many investigators to use other agencies to correct the tendency to strip. Particularly so is this true of Dr. Winterkorn. In the paper referred to above, he suggests that certain primers, not necessarily of an asphaltic type, may aid in preventing stripping. Whether they would be cheaper than other aggregate sources is for the individual to determine. It should, however, be demonstrated first that such primers are permanent. Heating will, in many cases, correct stripping faults as was evidenced by heating quartz (a material which strips readily) to a dull red heat after which it did not evidence any stripping.

How serious is stripping in the completed roadway?

It is my observation that for light oils it is serious because rising waters in the base will cause migration of the oil upward, enriching the top, with the likelihood of instability as exhibited by corrugations.

In the heavier oil, I am not so sure that it makes an appreciable difference providing the material (mineral) is amply protected either by densification of the mix or a proper seal coat, using an aggregate that does not strip.

On a recent trip in Texas with W. H. Wood, Materials Engineer of the Texas Highway Department, we examined one place on a section of inverted penetration in which there were particles which had stripped to the extent of having practically no adhering asphalt; yet this road was in excellent condition and seemed to be none the worse for stripped particles.

In preparing this article for discussion, I have tried to outline briefly some of the efforts that have been made to solve the stripping problem from the laboratory standpoint. Much apparently is left to be desired in both the tests and the materials we have to work with, especially the asphaltic binders In closing I should like to commend to you the paper by Mr. E. F. Kelley, Chief of Division of Tests, B. P. R. in the 1937 Proceedings of the Highway Research Board, and the paper prepared for the Montana National Bituminous Conference at Edgewater Park, Mississippi, by Dr. Hans F. Winterkorn of the Univers. ity of Missouri, both on the subject of adhesion of bitumen to mineral aggregates.

SAN CARLOS INDIAN CATTLE

cattle on the reservation are owned by individual Indians, there being about 600 brands totaling 25,000 head of cattle. In the recent dispersal of the famous Painter Hereford herd in Colorado, Domino C366, reputedly one of the top bulls in the nation, was sold to the San Carlos Indians. In the same bargain one of his yearling offspring bulls also came to the reservation. For many years, we have been buying registered bulls for replacement on the various ranges, but with the acquisition of such prize animals as Domino C366 and his offspring, we plan on raising on our own. These two bulls will be bred with the select of our registered females and we plan to take the best part of Ash Flat range as a strict ly registered herd pasture, it being the most accessible and choicest. In fact the Tribal Council has just passed an ordinance to that effect. Artificial insemination is being studied by our stockmen with the thought in mind of extending the usefulness of these two great sires. Naturally, all pertinent information relative to artificial insemination will be taught to the Indians. All other phases of good stock raising have been given them.

Since the inception of Indian Emergency Conservation Work on the San Carlos Reservation, the projects accomplished have been those which will greatly aid in the working of cattle. Over 400 miles of boundary and range division fences have been built, almost 100 earthen and concrete water tanks have been constructed, stock drives cleared, springs and wells developed. These emergency appropriations have given the Apache a new lease on life. The work has taken him to all sections of his domain, it has given him added income, and a greater realization of the possibilities of self-support. The San Carlos Apache already has self-government, given to him through the Wheeler-Howard Bill of 1934. All tribal affairs are controlled by a representative tribal council, composed of seven elected members of the tribe, one of which serves as chairman. The New Deal has meant a great deal to the San Carlos Apache. Indian Emergency Conservation Work came just at the time when the cattle working facilities were badly in need of repair.tired, came to San Carlos in 1923 and with him came a new era for the Apaches. Expired grazing leases were not renewed. Considerable pressure was brought to bear through Washington channels to have the leases renewed but Jim Kitch and the Apaches were successful in their stand. At the present time, there are no white cattle growers leasing grazing land from the Apaches and it is the intention of the administration that there will be none in the future.

We have now what is generally recognized as the largest registered herd of Herefords in the Southwest. Some 600 registered Herefords were purchased during the drought in 1934 by the government for the San Carlos Indians. The number has increased to 1200. Registration will be kept on 400 of these, and the balance will be used as a breeding herd for reimbursable heifers. Young male Indians over 21 years of age, of good character and desirous of going into the cattle business are chosen by the Tribal Council annually, as recipients of 20 head of choice yearling heifers. The young Indian is given ample time to repay the tribe for these heifers, and as sales are made from offspring steers under his brand, a small semi-annual payment is taken. The registered and purebred herd is owned by the tribe. Other The reservation grazing area is divided into 15 distinct or associated ranges. Clans, or family groups, have been assigned each range and cattle associations with elective officers at their head have been formed. It has been the practice of the San Carlos Apaches to sell or butcher all undesirable animals running on the range. All scrubby, off-colored and inferior stock is disposed of as soon as they are rounded up. Each cattle association takes on the working appearance of a large cattle ranch, or better yet, a cooperative livestock organization. Roundups are held every Spring and Fall; calves branded; steers de-horned; the cutting out of cattle offered for sale; and repairs made to cattle association equipment. Current market prices greatly determine the class of cattle offered for sale. Invitations to bid are sent to the most reputable cattle buyers in the Southwest. Sale cattle are divided into various classes and bids received for each lot, either by head or pound. Bids are opened, read, and sold to the highest bidder when all cattle association members owning cattle in the sale herd have agreed that the price offered is suitable. At a September sale of 1900 head, 400 head of yearling de-horned steers brought a top price of $37.96. This year, the Indian Office has not notified us of our comparative standing with other reservation in the number sold and average price received, but we feel sure that our standing will be about the same as in 1937. For 1938, we have sold almost 11,000 head for an average of $32.00 per head. A grazing fee of $5.00 per head sold is deducted on every head from each cattle check made out to the Indian cattle owner. Roundup chuck, the pay of roundup cooks and flunkies, foremen and general roundup expenses are paid from this fund. The purchase of salt and cottonseed cake for bull feed is also paid from this fund.

As yet, the cattle management plan is not perfected. Though leading the Indian Service in the number sold and money taken in, several phases of our cattle program are to be enlarged. About 400 of the 700 families on the Reservation are numbered as cattle owners. What to do with the remaining 300 is the big problem facing tribal leaders. The Tribal Council has just passed an ordinance setting off a big portion of the eastern range, recently vacated by the Double Circle Cattle Company, as a Tribal herd pasture. The plan will be to graze a herd of approximately 5000 head of cattle for the benefit of all members of the tribe over 65 and not cattle owners, widows, orphans, crippled or blind. The San Carlos Apache is endeavoring to establish his own social security.

HUACHUCA AGAVE NEAR ELGIN.

Upon the retirement of James B. Kitch as Superintendent in August in 1937, Ernest R. McCray was transferred from the Mescalero Apache Reservation in New Mexico where he had served as Superintendent for three years. In reality it is a homecoming for Mr. McCray, as he was Principal of the San Carlos Indian School before being appointed to a Navajo post at Shiprock in New Mexico. Mr. McCray returns to the San Carlos Apaches with an excellent record of Indian Service. Mainly through his efforts the Mescalero Apaches are recognized as one of the leading Indian tribes in economic and social security. The housing facilities he made possible for all members of the Mescaleros is one of the finest features of his work there. Beautiful four-room homes were constructed, using tribal lumber, logged and cut by the tribal mill. The homes are tribally owned and upon the death of the assigned member, the home is renovated and given to another. Such are his plans for the San Carlos Apaches. His will be a strenuous task. There is a decided need for a worthwhile program of adult education in other phases beside cattle raising. It might be fair to state that we hope we have one of the best Indian Day Schools, comparable to any public school system in the state. Headed by Timothy G. Mackey, a man who has given the major portion of his life to educating the young Apache in rudimentary subjects, our San Carlos Day School has made great strides in the last 15 years. It is for us to get behind all that is worthwhile, looking to the future when we may be self-supporting; when the people of the entire nation may say that at last, the Apache is a law abiding citizen; a self-supported and self-governed, respectable individual; and not, as our friend Bancroft once said, "Apparently the Apaches, non-progressing savages, ever the victims of injustices, must dwindle in number and finally disappear."

ARIZONA PECANS

(Continued from Page 5) Other trees from setting so many nuts they broke the limbs. They were to be had only by trial, error, and persistence.

Others joined in solving these primary problems. One of these was A. R. Heineman, who planted 22 varieties on his farm a few miles north of Creswell's. Ray Ward was another. In Salt River Valley, J. M. Schuele, Ernest Hall, Dr. F. D. Rowell and M. D. Ewing were among those who contributed to the growing pool of pecan knowledge. Recognizing the importance of the rising industry, the University of Arizona added a pecan specialist to its staff in Dr. Alton H. Finch. His individual work in the nut field finally caused him to be placed at the head of the horticultural department. By the time of Frank Creswell's death in 1936, three or four varieties had been proven to the point where they could be recommended without a single "if." It was known how to bring a pecan tree to bearing age in the best condition. But a brand new set of problems had arisen. Some of Arizona's advantages had turned out indirectly to be disadvantages.

First let us consider Dr. Finch's best known and possibly most brilliant suc-cess. This was in finding a cure for pecan rosette.

Just about everywhere in Arizona, except in Yuma Valley, a very mysterious disease appeared. Perfectly healthy pecan trees, young or old, would turn yellowish; the leaves would grow small and tend to bunch in "rosettes;" nuts would be few and mainly worthless; limbs would die back; often the whole tree died.

Dr. Finch decided that this must be a deficiency disease. Since it was practically non-existent in Yuma Valley, the soil or the water there must contain something that was lacking elsewhere. But what?

Again it was trial and error. Dr. Finch experimented with every element known to be essential to plant growth. He got no results whatever until he bored holes in the trunks of several badly rosetted young trees and poured in zinc sulfate. Next morning the yellow leaves were green. Miraculously the rosetting disappeared, the die-back stopped, those invalid trees became as vigorous and fruitful as any.

Rosette was marked off the list of pecan problems. A few cents' worth of zinc sulfate, worked into the soil around a tree, is insurance against that trouble for a yet undertermined number of years.

Other difficulties, however, were not vanquished so readily or simply. As Yuma Valley groves grew older they did not increase in yield as expected. A good many of the nuts were "blanks." They "failed to fill." The kernel inside many a plump shell was either a black wisp of nothing, or filled out at only one end.

"Too much vegetativeness," decided Dr. Finch after years of observation and thousands of tests. That is, the trees were growing too vigorously. Their strength was going mainly to the production of wood instead of nuts. The climate and rich soil were responsible. Mature trees, it was determined, needed different treatment than when young. Then the first object is to make them big so they will have plenty of fruiting growth. But when they get big they should slow down in growth, turn to bearing nuts. So a certain "starvation period" is advised, from blooming until harvest. There must be as little nitrogen in the soil as possible. Dr. Finch's recommended "control program" is bringing more perfect pecans and greatly reducing the percentage of blanks for those who follow it.

Then there is pre-germination. Late in the fall, while the "shucks" are still tight and green, nuts will sprout right on the limb. This trouble, like failure to fill, is more acute in Yuma Valley than elsewhere because that district has the longest growing season and the most humidity.

Growers had always waited, as in the South, for the shucks to dry and split as a sign of ripeness. In Yuma Valley this does not happen until late October or early November, and some shucks may remain green until frost.

Dr. Finch suspected that the nuts were actually ripe long before shuck splitting. There being no cold weather to dry the shucks, they just continued to hug the nuts. And a ripe nut, surrounded by a moist shuck, is very likely to sprout just as though it were stuck down in damp ground.

"Gather all nuts by October 15," Dr. Finch advised after chemical analyses had shown that they were ripe by that date. "Then treat them with ethylene gas and the husks will come off in 24 hours. The ethylene treatment is inexpensive, a mere matter of placing the nuts in a room or under a canvas and turning In a little gas. Gathering pecans by hand, however, is more costly than waiting for the shucks to divide and then thrashing them down with canes. But since it gets away from pre-germination loss, mid-October harvesting will probably become a general practice in Yuma Valley. It certainly will if pecan prices ever climb back toward former levels. Another advantage is that it insures getting new-crop nuts on the Thanksgiving market.

The Rainbarrel Of The Desert

(Continued from Page 9) How to get some returns from the land while waiting for a pecan grove to begin bearing, has been a puzzle from the start. Hegari, alfalfa and other "intercrops" have been grown between the trees, with varying results. In the last few years some of the most successful growers have combined sheep raising with pecans. They simply let the grass and weeds grow in their groves, turn in enough sheep to keep the growth eaten down. No cultivating is done, except an occasional disking to help mix organic matter with the soil. Irrigation is by flooding. Both the trees and the sheep thrive, and the nut yields are at least as satisfactory as in groves handled by other methods. Almost as many sheep can be pastured as though the trees were not there.

Marketing? That's always a rub, no matter what a farmer grows. When Arizona produced only a few tons a year of those high-grade extra-large papershell pecans, the home market took them all and Californians were lucky if they could be spared a few pounds. But rising volume, competition with cheap wild pecans from the South, and shrunken national buying power, have changed the picture fast. The growers are being led inevitably toward co-operative selling. One group has already been formed at Yuma to establish the State's first pecan crackery and storage warehouse. The lower grades of nuts, those with hard shells or shells accidentally broken, will be run through the cracking machine. Meats will then be sold in vacuum-packed jars and cans for use in confection and bakery goods, where consumption is always heavy. Whole nuts will be sold in cellophane, in burlap bags, in wooden containers-but always as Arizona pecans and always in strict accordance with grade. Those grades are set up under State law fostered by the industry. Everyone is agreed on the necessity for co-operating in packing, in shipping, in advertising, and in finding new outlets.

The longer roots and the greater number ran up hill. There are more things underground on the desert than on top. If you ever get a glimpse you always feel you are walking on a mine of mystery ever after. Thanks to the rain barrel and the compass you are no longer thirsty and lost but you haven't had your delectable confection yet. Of the three friendly services offered man by the Candy Cactus the most romantic is Cactus Candy, but this is only the crude name given in modern times to the love token known and used through countless ages if a certain legend is as true and ancient as it purports to be. Here is the legend; judge for yourself whether it is good, honest lore or an excellent ad for cactus candy.

The Toltecs, the gentle and poetic ancestors of the Aztecs, first made the love token. They believed that the soul of a beautiful maiden, beloved of the sun-god, was imprisoned in this plant. The white pulp was the maiden's purity and the armor of thorns was bound around it to protect his love.

Out of this belief grew an elaborate wedding ceremony climaxing a most complicated love making. After the young man had ascertained, first from the mother, then from the father, and last from the daughter that his wooing was looked upon with favor he went away to the desert and searched until he had found a perfect specimen without fault or blemish. With his bare hands he then uprooted it and carried it to the doorstep of his sweetheart where he performed the incredible feat of removing the myriads of tenacious spines with his own strong fingers. After this he scalped off the tough skin with his teeth-stout fellow. Next the courageous lover cut round slices of the pulp and proceeded through the intricacies of a long candy making recipe, at last turning out a love token which no sweetheart could resist.

A tiny piece of this confection he might place between her lips and take the other side with his own. No signal was then needed the candy melted in their mouths, the lips of the lovers met-presumably for the first time and they were happy ever after. Try it yourself, it's the most touching little ceremony I've heard of and it ought to work. As well as any. The trouble those old timers took! If all their weddings had been set for summer time the lover could so easily have made for his bride a glorious coronet of bisnaga blossoms, more brilliant than precious jewels, which are well known for their powers to win the nuptial kiss. The bisnaga itself wears them as a coronet from July to September, a remarkably long blooming season. The flowers are from two to three inches long and half as wide, with forty or more petals and twenty sepals, the colors yellow to orange red. If the thought were not unjustly insulting to that handy old soul, Mother Nature, it would occur to most of us to think that the blooms of the bisnaga looked too perfect to be real, paper thin petals, curled and fluted with exquisite precision. A coronet to glorify any wedding.