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IC ROADS
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oe HIGHWAY RESEARCH _ |
UNITED STATES DEPARTMENT OF AGRICULTURE
BUREAU OF PUBLIC ROADS
2 ioe. SA
A BITUMINOUS MACADAM ROAD AFTER 21 YEARS OF SERVICE
For sale by the Superintendent of Documents, Washington, D. C. - - - - - - - - - - - - See page 2 of cover for prices
PUBLIC ROADS Giese
UNITE DES TATE SsDEPAR TIVE NIRORSAGR @GUISRUI gE: BUREAUSOLSPUBELGSROADS
G. P. St. CLAIR, Editor Volume 13, No. 6 August, 1932
The reports of research published in this magazine are necessarily qualified by the conditions of the tests from which the data are obtained. Whenever it is deemed possible to do so, generalizations are drawn from the results of the tests; and, unless this is done, the conclusions formulated must be considered as specifically foertinent only to the described conditions.
In This Issue
Page Rationalization and Simplification of Test Requirements For Liquid Asphaltic Materials . 89 The: Batching: Plantin Concrete Ravine Work7=. 2) sa emneennnn eaten 0m a nL Connecticut Avenue Experimental Road Now 20 Years Old . .... =. 2.2. =. =. 104
THE BUREAU OF PUBEIT@ ROADS ~~) = =) Willard Building aw ashinetons aes
REGIONAL HEADQUARTERS- - - - - - - - Mark Sheldon Building, San Francisco, Calif. Vv DD VSs i RiUGsls Ost Gas DISTRICT No. |. Oregon, Washington, and Montana. DISTRICT No. 7. Illinois, Indiana, Kentucky, and Michigan. Post Office Building, P. O. Box 3900, Portland, Oreg. South Chicago Post Office Building, Chicago, IIl. DISTRICT No. 2. California, Arizona, Nevada, and Hawaii. ENSUES TINS eon Florida, Mississippi, South Carolina, Mark Sheldon Building, 461 Market St., San Francisco, Calif Shepherd Building P. O. Bog Jy Nonteomeyaaamn DISTRICT No. 3. Colorado, New Mexico, and Wyoming. DISTRICT No. 9. Connecticut, Maine, Massachusetts, New Hampshire, New 237 Custom House, Nineteenth and Stout Sts., Denver, Colo. Jersey, New York, Rhode Island, andaViermont
Federal Building, Troy, N. Y. DISTRICT No. 4. Minnesota, North Dakota, South Dakota, and Wisconsin.
410 Hamm Building, St. Paul, Minn, | DISTRICT No. 10. Delaware, Maryland, North Carolina, Ohio, Pennsylvania, Virginia, and West Virginia. DISTRICT No. 5. Iowa, Kansas, Missouri, and Nebraska. Willard Building, Washington, D, C. Eighth Floor, Saunders-Kennedy Building, Omaha, Nebr. DISTRICT No. II. Alaska. Room 419, Federal and Territorial Building, Juneau, Alaska. DISTRICT No. 6. Arkansas, Louisiana, Oklahoma, and Texas. DISTRIGI Nos aldahorearleshe 1912 Fort Worth National Bank Building, Fort Worth, Tex: 403 Fred J. Kiesel Building, Ogden, Utah.
Owing to the necessarily limited edition of this publication it will be impossible to distribute it free to any persons or institutions other than State and county ofhcials actually engaged in planning or constructing public highways, instructors in highway engi- neering, and periodicals upon an exchange basis. Others desiring to obtain Pustic Roaps can do so by sending 10 cents for a single number or $1 per year (foreign subscription $1.50) to the Superintendent of Documents, United States Government Printing Office, Washington, D. C.
CERTIFICATE: By direction of the Secretary of Agriculture, the matter contained herein is published as administrative information and is required for the proper transaction of the public business.
RATIONALIZATION AND SIMPLIFICATION OF TEST RE- QUIREMENTS FOR LIQUID ASPHALTIC MATERIALS
By E. F. KELLEY, Chief Division of Tests, U. S. Bureau of Public Roads, and PREVOST HUBBARD, Chemical Engineer, The Asphalt Institute.
HE PURPOSE of test requirementsin specifications is toinsure that materials furnished to meet the spec- ifications will be suitable for the use for which they
are intended. The value of test requirements is meas- ured by the extent to which they fulfill this purpose. Test requirements may be of two types—first, those which describe the properties or characteristics of a product which it is essential that it possess if it is to be suitable for a given purpose and, second, those of a
restrictive nature which define characteristics which |
may or may not be inherent in a suitable product, and the presence or absence of which has no measurable influence on satisfactory performance.
It is evident that, so far as possible, tests of the first type only should be used in specifications. However, the selection of such tests is not always a simple matter because of the lack of sufficient data, and the situation is frequently complicated by the difficulty of eliminating tests of the second class. The latter serve no useful purpose and such prestige as they may enjoy is undeserved, but before they can be discarded it is commonly necessary to overcome the inertia due to years of unquestioned acceptance.
Unfortunately, many of the common test require- ments for road materials are of the second class. of obscure origin and possibly developed originally for a purpose foreign to their present use, they retain their place in specifications, sometimes for lack of adequate substitutes and sometimes because of established prece- dent. This is particularly true of the specifications for that class of road materials known as liquid asphaltic products, of which enormous quantities are now used in the construction and maintenance of low-cost roads. Many of the tests which are used at present in specifica- tions for these materials have been handed down from specifications for bituminous materials of an entirely different class, often semi-solid in character, which were never intended to be used for the same purposes as those to which liquid asphaltic products commonly are put in highway work to-day.
In any attempt to rationalize specifications each indi- vidual test must be carefully scrutinized to ascertain its actual value. What does the property defined by the test signify in connection with the use to which the mate- rialis to be put and how can this property be adequately controlled by use of the test? If satisfactory answers to these two questions can not be formulated, the test has no place in a specification. Many of the tests now in common use will fail when subjected to this scrutiny.
In addition to the need for selecting the tests for liquid bituminous materials on a rational basis, there has been an equally urgent need to simplify the test requirements in current use.
The lack of agreement among the various State high- way departments with respect to tests and methods of testing has created a condition which has been little short ‘of chaotic. It is unnecessary to go into details here as this has already been done.’ It is sufficient to
1 Cooperative Research and Standardization of Low Cost Road Improvement, by Prevost Hubbard, Eighth Annual Asphalt Paving Conference, 1929. Simplified Specifications for Liquid Asphaltic Materials, by E. F. Kelley, Ninth Annual Asphalt Paving Conference, 1939. Cooperative Simplification of Tests and Specifi- cations of Liquid Asphaltic Materials, by J. T. Pauls, Association of Asphalt Paving Technologists, January, 1932.
131072—32
Often |
state that a survey in 1930 of State highway depart- ment specifications for liquid asphaltic products showed that there were in use, including all variations, a total of 119 different tests. As the practice of the different States in specifying such products varied greatly with respect to the selection of tests required, it was too often impossible to compare the specifications of two States in order to ascertain whether they were using practically the same or entirely different materials for the same type of work.
In addition to the complications entailed by the practice of specifying different tests or combinations of tests to define the characteristics of materials of essen- tially similar character, there also has been no general
agreement regarding the test results, or test limits, which should be incorporated in specifications. The
net effect of the non-uniform practice with respect to the requirements for both tests and test results has been the establishment of an unduly large number of erades of material. This has placed on manufacturers the burden either of carrying a large stock of different grades or of being prepared to manufacture, on short notice, materials to meet the wide variations required by the specifications of the different states. Naturally, this has resulted in increased expense which ultimately has been charged to the consumer,
The disadvantages of the existing situation were manifest to all concerned and as a result there was in- augurated a cooperative undertaking designed both to simplify and to rationalize specifications for liquid asphaltic materials. This cooperation involved the highway departments of the various States, the asphalt industry as represented by the Asphalt Institute, and the Bureau of Public Roads.
STATES GROUPED BY REGIONS FOR PURPOSES OF STUDY
For convenience in carrying on the cooperative pro- gram the States were divided into five groups or regions, the division being made largely on the basis of the territory served by the principal groups of producers. The States in each region are as follows
Region No.1 —Maine, New Hampshire, Vermont, Massachusetts, Rhode Island, Connecticut, New York.
Region No. 2.—New Jersey, Pennsylvania, Delaware, Maryland, Ohio, West Virginia, Virginia, North Caro- lina, South Carolina, Georgia, Florida.
Region No. 3.—Michigan, Indiana, Illinois, Wiscon-
sin, Minnesota, Iowa, Missouri, Nebraska, Kansas, Oklahoma. Region No. 4.—Kentucky, Tennessee, Alabama,
Mississippi, Arkansas, Louisiana, Texas.
Region No. 8. North Dakota, South Dakota, Mon- tana, Wyoming, Colorado, New “Mexico, Idaho, Utah, Arizona, Nevada, Washington, Oregon, California.
As a preliminary to the cooperative simplification work it was first necessary to establish a basis for the comparison of the great variety of requirements in cur- rent use. Without such a basis of comparison there is no adequate means for establishing the value of present and proposed tests nor for comparing the specifications of one State with those of another, even for materials which may be essentially the same.
89
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ROADS Vol. 13, No. 6
SIMPLIFIED SCHEME OF ANALYSIS ADOPTED
To furnish this basis of comparison a definite test procedure for the examination of all liquid asphaltic products was proposed. This procedure, known as the simplified scheme of analysis, was designed to reduce the required number of tests for any product to a minimum and the attempt was made to select the tests on a rational basis so that, by proper selection, they would define the essential characteristics of all materials of this general class. )
Meetings, which were attended by representatives of the cooperating agencies, were held in the five regions early in 1931 for the purpose of considering the proposed simplified scheme of analysis and to formulate a program for the future conduct of the cooperative work.
As a result of these meetings the scheme of analysis was modified in some of its details and adopted for use in the investigation, for which a program was drawn up. This investigation was for the two-fold purpose of studying the adequacy of the scheme of analysis and developing data which would permit a comparison of different specifications and the materials furnished to meet them. The program provided:
(a) That the producers should submit to the State highway departments samples of their products which would meet State specifications in which they were interested commercially. ‘Two samples, varying as much inconsistency as possible while still complying with all specification requirements, were to be submitted.
(6) That each sample should be tested, by the producer and by the department to which it was submitted, in accordance with the requirements of the State specifications and also in accordance with the approved scheme of analysis.
(c) That each State highway department should test, both according to the approved scheme and for compliance with its own specifications, a sufficient number of deliveries of materials purchased for use to cover the range in characteristics likely to occur in each type of material.
The cooperative work contemplated in this program was begun immediately after the regional meetings and was actively prosecuted until its completion late in the year 1931. In connection with this work the producers submitted to the State highway departments 1,154 samples of liquid asphaltic road materials. These samples were furnished by 27 producing companies from 47 refineries. In some cases a particular product complied with the requirements of several States so that with respect to the number of different materials there were some duplications. Eliminating such dup- lications, the samples submitted represented 715 different products produced to meet approximately 200 State specifications for all grades of liquid asphaltic materials used throughout the United States. The samples were all tested by the producers prior to ship- ment and a large percentage of them were tested by the highway departments to which they were sent. Thus, in addition to the basic data which were desired, there were made available a great number of check tests on duplicate samples of the same material and, in the cases of the duplication of materials mentioned above, check tests on the same materials by several laboratories. In addition to the tests made on samples furnished by producers, the State highway departments reported tests on 361 shipments of materials purchased for use.
The cooperative program provided that the producers should furnish to the Bureau of Public Roads, for such tests as might be considered necessary, duplicates of all samples of materials sent to the State highway departments. It also provided that copies of all test results should be sent to the bureau by the producers and by the States.
These duplicate samples were received by the bureau but were not tested. The samples will be retained for a reasonable period for possible use in connection with questions which may arise later.
The test reports were received by the bureau from time to time during the summer and fall of 1931. Late in the year, as the testing work neared comple- tion, all of the data which they contained were placed in tabular form and distributed for the information of the cooperating agencies. The data contained in these tabulations give additional emphasis to the need for rationalization and simplification of the specifica- tion test requirements.
CLASSIFICATION OF MATERIALS BASED ON VISCOSITY AND DISTIL- LATION TESTS
The simplified scheme of analysis which has been followed in the cooperative work embodies two tests which are considered to be of major importance. These are the viscosity test and the distillation test. The viscosity test is made with the Saybolt-Furol viscosimeter at one of three selected temperatures, depending upon the character of the material and its intended use. The distillation test is included in the scheme of analysis to take the place of tests for deter- mination of asphalt content and loss by volatilization at different temperatures. The residue from the distillation test is subjected to tests for consistency and solubility in carbon disulphide, replacing similar tests frequently made on original materials or on residues from the volatilization and asphalt content tests.
In tabulating the data obtained in the cooperative tests, the materials were classified as to type on the basis of these two important tests.
The materials were first divided into three classes, depending upon the consistency of the residue from the distillation test, as follows:
1. Liquid residue (float test less than 25 seconds at 122° F.)
2. Float residue (float test more than 25 seconds at 122° F. and penetration more than 300 at 77° F.).
3. Penetration residue (penetration less than 300 SSR iy a igeed abe)
Each of these classes was further subdivided on the basis of viscosity, as follows:
A. Viscosity, Furol, determined at 77° F.
B. Viscosity, Furol, determined at 122° F.
C. Viscosity, Furol, determined at 210° F.
The nine types of material which result from this classification are shown in the following table:
Viscosity, Furol, at—
Character of residue Vo Resta gacess | 210° FF:
Us AGU as cee a See ne eee ee ae) oe 1-A 1-B 1-C Bb 1 OSt2 Sas oe a ee ee ee ae ea ees 2-A 2-B 2-C SPP ODetration: < Reels. oe eS eres eee ee 3-A 3-B 3-C
ek
August, 1932
PUBLIC ROADS
|
It is evident that materials of types 1—-A, 1—B, and 1-C are of the nonhardening or extremely slowly hardening variety and, irrespective of their original viscosities, could not be expected to develop an asphalt cement in place in a road surface. Materials of types 2—-A, 2—B, and 2-C yield a distillation residue too soft for a penetration test, but sufficiently viscous for a float test and therefore would be classed as slowly hardening products whose consistency might increase materially after application, but which could not be expected to develop an asphalt cement in place. Mate- rials of types 3—A, 3—B, and 3-C, yielding a distillation residue sufficiently hard for a penetration test, would be classed as products which will eventually develop an asphalt cement in place, the rapidity of hardening being indicated by the results of the distillation test.
A study of the tabulated data, which included also State specification requirements for the various mate- rials, showed clearly that many specifications in com- mon use do not make the important distinctions of the above classification. In a number of cases several materials of entirely different type were found to meet all the requirements of a given specification. For instance, it was found that certain materials of types 1—A, 2—A, and 3—A were submitted to meet the require- ments of a specification for a certain material desig- nated as 45 per cent asphaltic oil. The essential re- quirement of this specification was that the material should contain between 45 and 55 per cent of residue of 100 penetration. The three distinct types met this specification except that the material of type 3-A had an asphalt content slightly above the maximum speci- fied. The specification failed so far in defining impor- tant characteristics, that materials which developed liquid residues, float residues, and possibly penetration residues in the distillation test could all comply with its requirements.
The tabulated data with respect to specifications showed clearly the necessity for discarding many tests in current use if any simplification is to be effected. As an example, in one region the 51 specifications for liquid asphaltic products required a total of 44 different tests.
Early in 1932 a second series of regional meetings was held to consider the data which had been developed by the cooperative tests and to obtain an expression from the States on the adoption of the proposed sim- plified scheme of analysis for use in future specifications and the elimination of other tests which might be con- sidered unnecessary.
The proposed scheme of analysis has been modified slightly with respect to certain details in the method of making the distillation test, and the test for solubility in naphtha, which had been added to the original scheme in the first series of regional meetings, was eliminated by the majority of the States represented at the second series of meetings. Aside from these changes the simplified scheme of analysis, as considered at the second series of regional meetings, 1s substantially the same as the scheme in its present recommended form, which is given in the following paragraphs.
RECOMMENDED SIMPLIFIED SCHEME OF ANALYSIS FOR USE IN SPECIFICATIONS FOR LIQUID ASPHALTIC ROAD MATERIALS
1. Flash point: : a. Cleveland open cup for materials having a flash point of 175° F. or more. A. S. T. M. standard method D 92-24,
b. Tagliabue open cup ? for materials having a flash point of less than 175° F. Method approved by the Bu- reau of Explosives, 30 Vesey Street, New York City, and by the Interstate Commerce Commission (Regu- lations for Transportation of Explosives, etc., par. 227).
2. Consistency: A. Viscosity, Furol, A. 8S. T. M. standard method D 88-30. a. At 77° F. for dust layers, primers, and all prod- ucts which are applied without warming. b. At 122° F. for all products, including cut-backs, which are warmed slightly before application. c. At 210° F. for all highly viscous products which must be heated to approximately 200° F. or above before application and which have a viscosity of less than 300 seconds at this temperature.
B. Float test at 122° F. on materials having a viscosity, Furol, of more than 300 seconds at 210° F. A.S. T. M. standard method D 139-27.
3. Distillation—for all products:
Total distillate, by volume, at the following tempera- tures: 437° F., 600° F., 680° F.
A.S. T. M. standard method D 20-30 with the follow- ing modifications:
Sample distilled shall be 200 cubic centimeters, the weight of this volume to be calculated from the specific gravity at 60° F.
Bulb of thermometer shall be immersed to a point one- fourth inch above bottom of flask.
Condenser shall be water cooled.
Distillate shall be collected in 100-cubic-centimeter graduated glass cylinders and the amount of distillate shall be reported in percentages by volume of water-free material.
Distillation shall be stopped at 680 °F. and the amount of distillate read to the nearest cubic centimeter after the condenser has been allowed to drain thoroughly into the receiver. The total residue shall then be poured immedi- ately into an 8-ounce tin and allowed to air cool without covering to a temperature below its fuming point suitable for pouring. It shall then be stirred and poured into proper receptacles for additional tests.
Temperatures observed in the distillation test shall be corrected for the effect of the altitude of the laboratory in which the test is made. (See A. S. T. M. standard method D 86-30.)
4. Tests on residue from distillation:
a. Float test at 122° F. on all residues having a float of more than 25 seconds at this temperature and hav- ing a penetration of more than 300 at 77° F. (100 grams, 5 seconds.) A.S. T. M. standard method D 139-27.
b Penetration at 77° F. on all residues of less than 300 penetration (100 grams, 5 seconds). A. S. T. M. standard method D 5-25.
c. Ductility at 77° F. on all residues of less than 200
penetration at 77° F. (100 grams, 5 seconds). A. S. T. M. tentative method D 113-26T. d. Solubility in carbon disulphide—all residues. A. S. T.
M. standard method D 4-27.
2 Method of test for flash point with Tagliabue open cup: The Tagliabue open cup flash tester shall be used. ‘The instrument shall set firm and level.
Fill the metal bath cup with water having a temperature at least 20° F. below the probable flash point of the oil to be tested, leaving room for displacement by the glass oil cup, which is then placed in the bath.
Fill the glass oil cup with the oil to be tested to within five-sixteenths inch of its upper level edge. See that there is no oil on the outside of the cup, or upon its upper level edge, using soft paper to clean the cup.
Adjust the horizontal flashing-taper guide-wire in place. Suspend the thermome- ter, with its bulb well covered by the oil. Heat bath with small flame lamp having the flame so adjusted that it will raise the temperature of the oil at a rate of 214° F, per minute, without removing the lamp during the whole operation.
For viscous liquids it is necessary that the liquid be stirred at intervals during the test.
Remove air bubbles, if any, from the surface of the oil before first trial for flash is made.
At the proper trial temperatures, noted below, try for flash with a small bead of flame (not over one-eighth inch) by drawing it quickly and without pause across the guide wire from left to right.
The temperature at which the first or initial flash is obtained is called the flash point.
Trial temperatures: For materials which may be expected to flash at about 80° F., try for flash at 70° F., then at.75°, 77°, 79°, 81°, 83°, and 85°. For other materials try for flash first at a temperature about 20° F. below the expected flash point and then try for flash at every 5° F.
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MUCH PROGRESS MADE AT REGIONAL MEETINGS
The discussions which took place at the second series of regional meetings related entirely to the adoption or elimination of test requirements and no attempt was made to set up test limits for specification purposes. The action taken at the meetings was quite informal in the sense that the acceptance or rejection of a test by a State was considered to represent the intent of that particular State with respect to its own specifications and the action of a majority was not considered as binding on the minority.
The important accomplishments of these meetings, which were attended by representatives of 30 of the 48 State highway departments, are summarized as follows:
The adoption of the tests for flash point, as given in the simplified scheme, was practically unanimous, as was also the adoption of the Saybolt-Furol viscosity test to replace the Engler test. With few exceptions it was agreed that the temperatures at which viscosity determinations would be made would be 77 ia SS F., and 210° F. It was also generally agreed that the float test at 122° F. would be used for materials having a viscosity, Furol, of more than 300 seconds at 210° F.
With two exceptions, the distillation test as described was adopted for cut-back materials by all the States represented, but the majority were not prepared at present to extend its use to materials other than cut- backs. A number announced the intention of making a further study of its suitability for the materials not classed as cut-backs. Discussion of this question led the representatives of the States in region No. 3 to define cut-backs as follows: Cut-back asphalt is a liquid asphaltic product which, when distilled to 680° F., yields a residue of less than 300 penetration at 77° F.
Tt was generally agreed that the end point of the distillation test should be 680° F. and that the volume of distillate should also be determined at 437° F. and 600° F. One region agreed to use no other tempera- tures. One region added another cut at 374° F:; another made the use of this temperature optional; and the other two regions added to it the tempera- tures of 302° F., 320° F., and 500° F., with the general agreement that not more than four temperatures in addition to that of 680° F. would be used in any one specification.
The agreement to adopt the proposed tests of residues from the distillation test was practically unanimous.
With respect to the elimination of tests not included in the simplified scheme of analysis, there was less unanimity of opinion than in the case of the tests in- cluded in the scheme, but, in spite of this, considerable progress was made.
As has been noted, the agreement to replace the Engler with the Saybolt- Furol viscosimeter was practically unanimous and only a small minority expressed the
intention of retaining the test for insolubility in naphtha. However, a large majority favored the re-
tention of the test for the determination of asphalt content, particularly for materials other than cut-backs, until such time as it is more definitely established that the tests in the simplified scheme are adequate to replace it. A large number of those who favored the continued use of the asphalt content test also favored a ductility test on the residue.
About half the States represented at these meetings will continue to use the Bee er test (loss on heat- ing for five hours at 325° F.) for the time being, at least, although of these cee half will use it only for
materials other than cut-backs. The States retaining the volatilization test generally will retain also pene- tration or float tests on the residues from volatilization.
The volatilization test at 212° F., which has been used to a limited extent in the past, was rejected with only one dissenting vote. The elimination of the test for fixed carbon was also practically unanimous.
The test for the determination of paraffine scale, concerning which there has been much discussion during the past few years, particularly in the States of region No. 5, received, in the various meetings, only one vote for its retention. It is known, however, that at least one other State, which was not represented at the meetings, will continue to use the test in spite of its questionable accuracy and problematical value.
The test for solubility of original materials in carbon tetrachloride will not be continued to any extent except in one region.
The vote for the elimination of specific-gravity de- terminations on original materials and distillates and float tests on original materials at 77° F. and 90° F. was so nearly unanimous that their continued use will be practically neghgible.
This summary of accomplishment evidences a truly encouraging progress in the simplification program, particularly when one considers the relatively short time during which the cooperative effort has been carried on. However, much remains to be accomplished before the program can be brought to a satisfactory working basis. Misunderstandings and misconcep- tions must be cleared up and a more complete know- ledge and understanding of many details must be obtained. Asan aid in this direction it is believed that a discussion of the logic of the proposed simplified scheme of testing and a critical analysis of other tests still in common use in certain regions will be of service. ESSENTIAL PROPERTIES TO BE DEFINED IN SPECIFICATIONS FOR
LIQUID ASPHALTIC PRODUCTS
Without regard to the individual tests which may be used for the purpose, it seems important to specify cer- tain fundamental properties of liquid asphaltic products, depending upon their method of use and the purpose which they are expected to serve. Of these, the most important appear to be:
1. Original consistency.
2. Ultimate consistency as representing the material developed after application.
3. Relative rapidity of the change, if any, from origi- nal consistency.
4. Amount and character of active bitumen remaining after application,
Original consistency—The determination of con- sistency of the original material is essential and, in the case of hquid asphaltic products, it is commonly as- certained by a test for viscosity. Some form of viscosity test almost invariably has been incorporated in specifica- tions for materials of this character. The method chosen for determining viscosity of highway materials usually has involved the use either of the Engler viscosi- meter or of the Saybolt-Furol viscosimeter, the test being made with each instrument at a variety of temper- atures ranging from 77° F. to 212° F.
As has been noted, the decision to substitute the Saybolt-Furol test for the Engler test in the simplified scheme of analysis was practically unanimous and it was generally agreed to make the viscosity determina- tions at temperatures of 77° F., 122° F., and 210° F. The primary reason for the selection of the Say bolt- Furol instrument in preference to the Engler is the
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considerably shorter time which is required for the test. The availability of apparatus with multiple tubes and an accurate, automatic temperature control are added advantages of the Saybolt-Furol test.
The maximum temperature originally proposed for the viscosity test was 212° F. (100° C.), but this was changed to 210° F. the use of an oil bath instead of a water bath.
The
difference between the two temperatures is not par- |
ticularly important, but the advantage, if any, gained by the change to 210° F. is not general, since in labora- tories located at altitudes much over 1 000 feet above sea level the oil bath must be used for either temperature.
The viscosity, or resistance to flow, of all liquid bituminous materials may be decreased by raising their temperatures, but the decrease in viscosity per unit rise in temperature often varies greatly for different prod- ucts. Therefore, a given viscosity value at an elevated temperature, such as 212° F., by no means indicates the viscosity or consistency of the product at a more normal temperature.
Consequently, it is desirable when possible to ascer- tain the consistency of bituminous road materials at what may be considered a normal temperature. Since
° F. has been accepted generally as an average normal temperature, it is desirable to make the viscosity test at this temperature when it is possible to do so satis- factonly. However, many of the liquid asphaltic products are so highly viscous that a_ satisfactory determination at 77° F.can not be made. Insuch cases it is necessary to make the test at some elevated tem- perature, and this preferably should be within the range to which the material may be subjected in service subsequent to its application. A temperature of 140° F. represents the approximate maximum of this range. Many materials which are too viscous to be tested at
° F. may be tested accurately at 122° F., and this test temperature, which is within the service range, has come into quite general use for such products. In the proposed simplified scheme of analysis, therefore, 77° F. and 122° F. were put forward as being satisfactory temperatures for the great bulk of products now in use.
Some products so nearly approach the semisolid state in original consistency at normal temperatures that satisfactory viscosity tests can not be made on them even at a temperature of 140° F. or considerably higher. For such products the temperature of 210° F. has been adopted. As a result of further consideration of the matter and subsequent analysis of the cooperative test data, it now appears that it might be advantageous to eliminate determinations of viscosity at this high tem- perature and substitute the float test at 122° F. as a measure of consistency of those products which can not be tested for viscosity at 122° F.
It seems highly desirable to control the consistency of all materials by tests at temperatures within the range of those encountered in service subsequent to application. At the present time the float test appears to be the only acceptable test which is satisfactory for such determinations when the material is too viscous for a viscosity test and too soft for a penetration test within this range of temperature. While it can not be translated accurately into terms of viscosity or penetra- tion for all types and grades of asphaltic material, nevertheless it gives an idea of approximate consistency which is far more significant than a viscosity test at oN bam Oe
As has been stated previously, the viscosity at 210° F. or 212° F. does not indicate consistency at normal
' practical purposes, therefore ) )
to eliminate the general need for |
temperature, and from the standpoint of the applica- tion of a material no record of viscosity at such an elevated temperature appears necessary. For all it is believed that the float test at 122° F. will be satisfactory as a measure of consistency of the class of materials which are too viscous for a viscosity test at 122° F. and too soft for a penetration test at 77° F.
Ultimate consistency as representing material developed after application.—tIn certain types of highway con- struction and treatment, liquid asphaltic materials are used in preference to the semisolid varieties to facilitate their application to or manipulation with the non- bituminous constituents of the roadway surface. If it were practicable to use a much more viscous product, such a product frequently would be used prefer entially to produce without delay the results which it planned to secure ultimately. In other words, while not in-
variably so, it is frequently desirable that the vise osity or consistency of the original material should become greater after it has been applied. Therefore, it is desirable to ascertain and properly describe in specifica- tions the approximate degree to which the original material will harden or increase in viscosity after use. Various tests have been used with this general purpose in mind, but comparatively few actually give the de- sired information for reasons which will be discussed later. Before the simplified scheme of analysis was proposed, these tests were carefully considered from all standpoints and it was concluded that the distillation test, with the thermometer bulb in the liquid rather than in the vapor phase, came nearer to giving the desired information than any other single test.
A distillation test carried to an end temperature of 680° F. has been used for some years by a number