Heat Stability of Typical Asphalt
Antistripping Compounds KENNETH J. L I S S A N T
AND
ALLEN H. F A R R
TRETOLITE GO. DIVISION, PETROLITE GORP.. WEBSTER QROVES 19, M O .
T h e heat stability of five nitrogen containing organic materials and seven commercial antistripping additives has been determined using four different asphalts and two different antistripping tests. Heat stabilities were determined after heating a t 200” F. for 1, 2, 3, 4, and 7 days. Heat stability i s defined as the percentage initial effectiveness retained after heating for a specified period. The relative heat stability is shown t o be a function of the type of chemical compound, t h e asphalt used, and t h e antistripping test used.
0
N E of the most trying problems in the use of asphaltic binders for road building has been the fact that most available aggregates are preferentially water-wetted. This makes it difficult or impossible to obtain complete coating of the aggregate with bitumen unless the aggregate is dry. The cost of drying the aggregate greatly increases the cost of the project and, where drying equipment is not available, limits the preparation and laying of the rock-asphalt mixture to periods of dry weather. As an answer to this problem, a number of antistripping additives have been offered for sale. The function of these additives is to cause the asphalt preferentially to wet the rock surface even in the presence of water. When dry aggregate is coated with bitumen and then exposed to water, the asphaltic film may rupture and the water penetrate between the binder and the rock. This stripping of the asphalt from the aggregate soon destroys the continuity of the stabilized surface. Additives, then, are designed to have two main functions. 1. They must make it possible t o coat wet aggregate with asphalt. 2. They must increase the resistance of the asphalt-rock bond to water. The asphaltic materials customarily used for road building are extremely viscous a t ordinary temperatures. Reduction of the viscosity to enable mixing with the aggregate is obtained in three ways, The bitumen may be heated, it may be diluted with a solvent, or it may be emulsified in water. Hot-mix procedures are usually preferred where possible. Cutback asphalts are widely used in road construction and maintenance. Much work is also done with asphalt emulsions. Additives are usually not needed to promote coating in hot-mix applications. They are sometimes added to increase the water resistance of the final surface. The antistripping additives have been most widely used to promote coating of moist aggregate by cutback asphalts. They are also receiving increased notice for use in asphaltic emulsions to increase bonding of the asphalt to the rock. Many methods have been suggested for the testing of asphalt additives. Each test usually specifies a standard aggregate, a special method of mixing, a curing procedure, and a method of estimating stripping. None of the tests has proved completely satisfactory, Most of them involve the visual estimation of percentage of aggregate coated. An experienced operator becomes quite consistent in his estimates but may disagree with another operator by more than 10%. Some methods have been suggested to avoid this personal element. Photoelectric reflectance methods have not proved applicable. Many tests now only differentiate between completely coated and more than 10% stripped. For an excellent discussion of antistripping tests the reader is referred to the American Society for Testing 2276
Materials “Standards of Bituminous Material for Highway Construction, Waterproofing, and Roofing,” September 1954, Appendix I, pp. 425-34, American Society for Testing Materials, 1916 Race St., Philadelphia 3, Pa. Until recently, the question of the heat stability of asphalt additives has not received much attention. If the additive is added immediately prior to laying of the surface, it is not subjected to high temperatures for long enough to cause much trouble. However, when the additive is added to the asphalt a t the refinery and the hot mixture is shipped to the user, it may remain near 200’ F. for several days. It may then be reheated before unloading, and before use. Heat stability then becomes a vital factor. It must be emphasized that in conducting this study the relative effectiveness of materials tested was not considered. Each material was tested at the minimum concentration necessary to obtain satisfactory initial effectiveness. The percentage of additive used varied from 0.25 to 4%. The most common range was from 0.75 to 1.25%. The heat stability was taken as the percentage of initial effectiveness retained after heating. Data are given on two different stripping tests. The selection was based on the simplicity of the test and the ability of the test to give reproducible results. The tests are representative of many in common use. Four different asphalts were used. The tests were limited to cutback asphalts since they are the largest present market for additives and are most readily obtained and stored. Emulsions cannot be heated for extended periods and penetration asphalts are limited to hot-mix procedures. Many of the materials that have been suggested for use as antistripping additives are nitrogen containing organic compounds. A closely related series of these materials was selected for testing. A series of commercial samples was also tested. These commercial additives are proprietary organic mixtures. Elementary analysis shows all of them t o include nitrogen containing compounds. Experimental Procedure
Samples of 100 grams of the asphalts described in Table I were weighed into 4-ounce, wide-mouthed glass bottles. The required amount of additive from the group described in Table I1 was added to each asphalt. The mixture was heated to about 120’ F. and throughly mixed. A small sample was withdrawn from each bottle and the initial effectiveness determined. The tightly-capped, nearly-full bottles were then placed in a forced air, electrically heated oven and held at 198’ t o 210’ F. Small samples were withdrawn a t the end of 24, 48, 72, 96, and 168 hours. These samples were tested immediately for antistripping properties.
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 47, No. 11
Initial pH 6.0 11.5 9.1 West Texas and Kansas Wyoming 9.2
No. Source of Crude 1 West Texas and Kansas 2 Eastern U. 9. 3 4
II.
Table 1. 2.
3 4: 5.
to be tested were added. The aggregate was stirred with a spatula for 3 minutes. 3. The coated sample was allowed to cure for one hour a t room temperature. 4. The sample was covered with water and allowed to soak for I/* hour. Floating asphalt was skimmed from the surface of the water and the percentage of the rock surface still covered with asphalt was estimated.
Asphalts Used in Tests
Table 1.
M
M
KOH/8ram to pH 11 0.25
HCl/&am to pH 4 . 3
...
1.09 2.08 0.695
0:925 0.134
Type &IC-3 MC-3 MC-2 MC-3
Additives Tested Discussion of Results
An amine derived from coconut fatty acids An ester of crude tall oil and triethanolamine The disoap of crude tall oil and ethylenediamine A mixture of the disoap and diamide of crude tall oil and ethylenediamine The reaction product of a fatty acld and hydroxyethylethylenedlamlne
The stripping test results in Table I11 show that 1. In general, the additives are more effective initially on asphalts No. 2 and No. 4 than they are on asphalts No. 1 and No. 3. 2. Additives No. 2, 5 , and perhaps No. 1 are more heat-stable than No. 3 or 4. 3. Only additives KO. 2 and No. 5 retain their effectiveness for the full 7 days.
Two different antistripping tests were run. The first is a coating test typical of the specifications used by several state highway laboratories. The second is a stripping test similar t o that used by the state of Ohio.
The sand-coating test results in Table IV are more consistent and show that
Coating Test
1. The additives again seem to be more effective on asphalts No. 2 and No. 4. 2. All scores on this test tend to be lower. It may be said to
1. Samples of 20 grams of standard Ottawa sand and 25 nil. of distilled water were placed in a 2-ounce glass bottle. 2. One gram of the asphaltic material to be tested was added, being careful t o keep the asphalt on the surface of the water. 3. The bottle was stoppered tightly and shaken for 30 seconds. 4. The percentage of the sand that was coated was recorded. (The state highway tests require that the sand must be completely coated.)
be a tougher test. 3. The heat stability ratings are in the Bame order. Additives No. 3 and No. 4 show poor heat stability. Additives KO.2 and No. 5 show considerable effectiveness even after a full week.
The sand-coating test results for asphalts No. 1 and KO.4 are shown in Table V. The five additives were used again plus seven commercial additives. The concentration of additive No. 5 was one third of that used in Table IV. The results of interest are
Stripping Test
1. The additives are much more effective on asphalt S o . 4 than they are on asphalt No. 1. 2. Only additive No. 2 shows stability for the full week on asphalt No. 1. 3. At the lowered concentration, additive No. 5 shows poor
1. Samples of 50 grams of both Ohio pea gravel and Ohio limestone were placed in an 8-ounce flat metal pan, covered with water, and soaked for 1/2 hour. 2. The excess water was drained and 5.5 grams of the asphalt
Table I I I . Compound 1 2
Initially -Asphalt 75
S o . 1,
50
5
98
1
75
Asphalt 66 100 85
2 3 4 5
50
70 50 98
100 100
November 1955
Initially
1
7
Initially -Asphalt 85 70 70 60 98
100
50 50 100
27 100 50 50 100
No. 3, % Effective80 66 66
66
53
100
80 100 100
80 SO
100
100
100
56 80
85
100
100
100
Table IV. Compound
4
% Effective-
27
53
100 100 100 100
3 4
90
2
1
Heat Stability Stripping Test
Days 3
2
53
100
100
36 80 100
100
36 80 100
1
X o . 2,
100 100 100
83 100
-Asphalt 90 90 85 80 98
2
100
90
100 100
100
47 35
100
83
100 S o . 4,
55 90
100
88 100
Days 3
4
7
59 70 71 42 100
29 70 57 42 100
% Effectiv94 42 85 83 100
yGEffectiv100
78
100
71 67 100
78 95 69 67 100
Days 3
4
7
82 88 100
78
Heat Stability Sand Coating Test
Days 3
4
1 2 3 4 5
99 95 95 70 98
-4sphalt KO.1, yo Effectiv80 50 100 80 100 100 100 100 0 0 0 11 0 0 0 14 100 100 100 in0
1 2 3 4 5
95 95 20 50 98
Asphalt No. 3, YGEffectiv74 63 85 85 100 95 100 100 0 0 50 0 40 0 0 0 100 100 100 100
7
Initially
1
Asphalt 20 95
0
0
100
32 95
0 0 100
95 80 90 70 98
-Asphalt 95 95 90 80 98
95 100 100
71 100
2
No. 2, yo Effectiv85 85 85 100
95 71 100
100 66 57 100
100
45 57 100
85
100
33 28
100
No. 4, % ’ Effective-
85
100 100 100 100
85 100 95 87
010
85 100 66 37
100
INDUSTRIAL A N D ENGINEERING CHEMISTRY
74
100
56
37 100
74 100 45 37 100
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ENGINEERING, DESIGN, AND EQUIPMENT Table V. C o mpound 1 2
3
4 5
B C
D
E
F G
K
Initially -Asphalt 95 98 80 60 90 95 98 80 80 95 90 85
1 100 100 62
33
Days 3 4 No. 1, Effectiv2
85 100 62
33
89
78
10 12 12 10 11 12
10 12 12 10 11 12
63
63
21 100 50 0 33 52 0 0 0 0 0 0
21 100 25 0 0 42 0 0 0 0 0 0
7 5 97 0 0 0 21 0 0 0 0 0 0
Initially -Asphalt 98 98 90 95 95 90 98 95 95 95 95 95
stability on asphalt KO. 1 but retains its effectiveness on asphalt KO.4. 4. The commercial additives are not distinguished for their heat stability. None of them is effective on asphalt No. 1 and only F shows full stability on asphalt No. 4. The data show that none of the additives tested were equally effective on all asphalts. T h e triethanolamine derivative is the most promising of those tested. A close second is the reaction product of hydroxyethylethylenediamine. A manufacturer of an asphalt of type No. 2 or No. 4 would have little difficulty finding an effective additive, particularly if he could keep the heating time below 3 days. On the other hand, a user of an asphalt similar t o type No. 1 would have t o use substantially more additive and would be greatly limited in his choice. The basic reasons for heat instability are not yet fully clear. Work is progressing on this question and it is hoped that a later paper can deal with this matter more fully. However, some general postulates can be made. It can be assumed that instability is brought about by three closely related processes. 1. The additive decomposes when heated. 2. The additive reacts further t o produce a less effective compound. 3. Thc additive reacts with some constituents of the asphalt to produce a less effective compound. When amine carbonates are used as additives, they release carbon dioxide on heating and cause foaming of the asphalt. This is an example of the first reaction. Amine acetates may also decompose when heated. An example of reaction KO.2 may be the case of additive 4, Table 11. If the disoap in the mixture dehydrates to form more diamide, and if the diamide is less effective, then the recorded instability would be explained. The additives were less stable in asphalts No. 1 and KO. 3 than in asphalts No. 2 and No. 4. Table I shows that these two asphalts have lower pH and higher titer than the other two.
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If these acidlike constituents are able to react with the amine Days groupings of the additive to 2 3 4 7 produce less effective materials, No. 4, % Effectivea n answer t o the instability of 90 100 80 70 several of the compounds would 100 100 100 100 22 0 100 89 he indicated. 42 0 0 0 Compound 50.2, Table 11, 100 100 100 100 72 56 78 72 which contains only ester link92 100 51 100 84 89 95 52 ages and a highly hindered ni89 93 100 73 trogenatom seemstobethemost 95 100 100 95 42 63 100 90 stable. It may be that it is in85 42 100 90 trinsicallv more stable to heat and that it cannot react further with the asphalt acids. Or if it does react, the products may also be effective antistrippers. Compound KO. 5 with a terminal hydroxyl and partially blocked amine groups is also more effective after heating. At low concentrations, however, i t does show loss of effectiveness in the acid asphalts. It may be that enough additive must be added t o the asphalt t o react with the acids before it begins t o be effective after high temperature exposure. As yet not enough work has been done t o determine which mechanism is most important. It should be emphasized that in conducting these tests the relative effectiveness of the compounds as antistripping agents was not considered. Each was used a t the minimum concentration for satisfactory initial effectiveness. The data, therefore, show only relative heat stability and not over-all relative effectiveness.
Heat Stability Sand Coating Test 1 100 100 100 52 100 78 100 95 100 100 100 100
References
Am. SOC.for Testing Materials Standards on Bituminous Materials for Highway Construction, Waterproofing, and Roofing, D 244-49, 105-117 (1949). Ibid., D 589-46, 5-6 (1946). Ibid., D 9 4 6 4 7 T , 1-2 (1947). Ibid., D 977-53, 3 4 (1953). I 6 i d . , D 597-46, 7-8 (1946). Ibid., D 1074-52T, 162-6 (1952). Ibid., D 1075-54, 158-9 (1954). Barth, Edwin J., Petroleum Refiner, 2 1 , 232-9 (ilugust 1942). Critz, Paul F., and Goode, Joseph F., Roads a n d Bridges, 84, 50-6, 108, 110, 112-14, 116, 118 (August 1946). Hemmer, Lucien, Fr. Patent 826,789 (April 1938). Johnson, James M., U. S. Patent 2,386,867 (October 1945). Mikeska, Louis A., Can. Patent 425,128 (December 1942). Mikeska, Louis A., U. S. Patent 2,361,488 (October 1944). Monson, Louis T . , Ibid., 2 , 6 7 9 , 4 6 2 (May 1954). Tremper, Bailey, and Erwin, Richard P., Proc. M o n t a n a Natl.
B i t u m i n o u s Conf., 4, 102-10 (1938).
Williams, Harold G., Brit. Patent RECEIVED for.review April 5, 1955.
INDUSTRIAL AND ENGINEERING CHEMISTRY
(January 1943). ACCEPTEDAugust 5, 1955.
554,986
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