INDUSTRIAL AND ENGINEERING CHEMISTRY
546
is in itself a measure of the shape factor, since the weight of the particles is obtained from Equation 1 by multiplying by the density W
Since D and
p
= 6p
NDS
(2)
are known and may be considered constant, 6
W KN-
(3)
Hence, the shape factor is as accurate as the average weight of the particles constituting the sample. Average particle weights were obtained by counting all particles from several portions of each sample, and reweighing. The results of this procedure are given in Tables I and 11. The tables show that the average particle weights as determined above are not constant. Nor does there appear to be any trend toward constancy, even when large numbers of particles are counted. The probable errors of individual samples are 6.9 and 12.5 per cent, which may be considered as being rather large. The shape factors calculated from Equation 1 for the samples in question are 0.17 and 0.15, respectively (taking p = 2.65). These values correspond with the shape factors determined by Hatch and Choate for very small particles (3). These investigators obtained volume-shape factors as low as 0.14 for particles of the order of 10 microns (0.001 cm.). Actual particle counts, however, were not made, but obtained by an indirect procedure.
VOL. 11, NO. 10
Without question, the size distribution of the aggregate is most important. A small number of large particles can alter the ratio of WIN although no significant change in the size distribution, and hence the average diameter, is apparent. The volume of a particle is as the cube of the diameter. Hence, a single particle of an aggregate with a diameter 10 times that of the smallest has a volume (and mass) equivalent to 1000 particles of the latter. This fact undoubtedly acIcounts for the differences in average particle weights. (As a matter of experiment, the extremes of size-frequency plots vary from sample to sample without materially affecting the average or the median sizes.) It is questionable whether a size-weight distribution for calculating average diameters would yield better results since, as Hatch has pointed out, summation curves by weight and count will plot as parallel lines on logarithmic probability paper (2). It may be concluded, therefore, that the best value of the volume-shape factor is that determined from the average particle weights of several aliquots of the aggregate, each including a large number of particles.
Acknowledgment The authors desire to acknowledge the assistance given them by Richard W. Schayer. Literature Cited (1) Goldman, F. H., and Dalla Valle, J. M.,Am. Mineral., 24,40-7 (1939). (2) Hatch, Theodore, J. FranlcZinInst., 215,27(1933). (3) Hatch, Theodore, and Choate, S. P., Zbid., 207,389(1929).
Judging Adhesiveness of Bitumen to Silica Sand A Comparison of Mixing Method and Wash Test HANS F. WINTERKORN A N D GEO. W. ECKERT Missouri State Highway Department and University of Missouri, Columbia, M o .
T
H E fact that a certain parallelism exists between wetting and adhesiveness phenomena has tempted a number of investigators to apply the principles and methods of flotation to the problem of testing and improving the adhesiveness of bitumen to mineral aggregate. The inherent theoretical and practical limitations of such an undertaking have been outlined previously (4). Here it need only be mentioned that while wetting phenomena are usually instantaneous, the development of maximum adhesion between a mineral surface and bituminous material is a function of time. A recent contribution applying flotation principles to the problem of bitumen adhesion is the work of McLeod (b), who while using activators and wetting agents assumes that the ease of covering wet Ottawa sand with asphaltic bitumen is a measure of adhesiveness. Since the ease and speed with which the mixing test by McLeod can be performed would represent an advantage over the more lengthy procedure of the commonly used wash test (1, b, 6), it appeared desirable to compare results of these two tests on the same set of samples.
Experimental Procedure The testing procedures used were the mixing method as reported by McLeod and the wash test with a machine previously described by the authors (6). For the experiments on mixing, Ottawa sand wm thoroughly washed with distilled water and dried, and the fraction passing No. 8 and retained on a No. 4-0 sieve was employed, Two asphaltic materials having the properties given in Table I, and 0.05 N solutions of sodium oleate and activator salts, respectively, were used for the tests. A
preliminary experiment showed that various MC and SC oils had different mixing efficiencies with the sand in the presence of water. However, the addition of from 0.2 t o 0.5 cc. of 0.05 N sodium oleate solution to any of the asphalt-sand-water mixtures resulted in a complete stripping of the coated sand and the balling up of the asphalt into numerous particles. The addition, thereafter, of the activator solutions had different effects, varying with the concentration and type of compound. The mixtures for testing adhesion were made in the following manner: Thirty grams of sand and 1 gram of asphaltic material were thoroughly mixed in the presence of water, enough water being added to cover the sand and the excess drained off.
T A B LI.~PROPERTIES OF ASPHALTS
Saybolt-Fuiol viscosity a t 122' F., sec. 8 ecific g r a v i p , 60° F./60° F. F&sh point, F. Ohensis Residue, % Penetration of residue a t 77' F., 100 grams, 5 sec. Ductility of +due at '77' F., om. Loss on heating 50 grams 5 hours at 325' F., %
Slow-Curing Road Oil No. 1 No. 2 171 327 1.0402 0.9766 240 260 Positive Negative 71.8 73.2 86 85 101 15049.92 8.36
Varying degrees of coverage were obtained. One-half cubic centimeter of 0.05 N sodium oleate was added and the mixture stirred; complete stripping occurred. The activator solution w m added in 0.1-cc. increments with thorough mixing after each addition untiI the sand was uniformly coated or until it was seen that no coating would be accomplished.
OCTOBER 15,1939
ANALYTICAL EDITION
The adhesion data and mixing observations are given in Table 11. The adhesiveness tests were made after the samples had cured in air 3 days and then stood in water one clay.
Results Asphalt 1, when mixed with the sand in the absence of water, wetting, and activating agents gave a very good coating, and after the same curing period as described above gave the best possible adhesion. Mixed in the presence of water, the mixing was still very good, whereas after the same curing period as above the asphalt stripped a t 60" C., being not affected a t 30" and 46" C., which can be called fair adhesion. Asphalt 2, when mixed with the sand in the absence of water, wetting, and activating agents, gave a poor mix and poor adhesion. Mixing and adhesion were also very poor when this asphalt and sand were mixed in the presence of water. These two asphalts provide the two extremes for observation-e. g., very good and very poor adhesion. The data in Table I1 indicate a similarity in the results of mixing observations and adhesion tests if both activator and wetting agent are used. There is, however, no exact correlation, because several mixes which were very good on the basis of efficient mixing gave poor adhesion. These cases are magnesium chloride and silver nitrate with asphalt 2. These two salts also lowered the adhesion of asphalt 1. Since the wetting agent (sodium oleate) in the absence of an activator caused the complete stripping of the asphalts from the sand, the effect of omitting the wetting agent and adding only the so-called activator solution was investigated. Results of these experiments are given in Table 111. In this case, the amount of water present is more important than where the activator and wetting agent are used. These tests indicate that the salt solutions which are bad with soap are also bad when soap is not used. However, some of the salt solutions which have a good effect in connection with soap do not give good results when soap is not used. Lead nitrate appeared to be the best reagent in regard to both mixing and adhesion results, although potassium aluminum sulfate was almost as good. Calcium chloride, magnesium chloride, and silver nitrate were generally not good with regard to adhesion, although magnesium chloride and silver nitrate tended in proper amounts to give good mixing (with soap). Ferric chloride used without soap gave TABLE 11. MIXINGAND ADHESION DATA (0.5
Soap
Salt
Salt Solution,
Cc.
cc. of
sodium oleate used)
Mix Asphalt 1 Uniform
4 d h e s i p Vtluea 30 45 60 70'
Uniform Uniform Uniform Uniform Uniform Uniform Uniform Uniform
Uniform
Asphalt 2 Coating Uniform 1 1 1 1 1 Co(N0o)z 0 . 2 1 1 1 Uniform 1 2 KAl(SOd3 0 . 1 1 1 Uniform 1 1 3 FeClr 0.3 1 1 1 Uniform 1 4 P b ( N 0 d r 0.1 Uniform 1 1 1 1 0.2 5 ZnSO4 .. , . 6 AgNOs 1 . 2 Poor until 1.2 cc. were added 3 Very poor 3 .. .. .. 2.1 7 CaCln 1 Good 1 1 1 0.1 8 BaCh 3 .. .. 9 MgClz 0 . 5 Poor until 5 cc. were added 2 1 1 Uniform 1 1 10 cuso4 0.1 a 1 = no stripping, 2 = 25% or less stripped, 3 = more than 25% stripped. .
I
541
TABLE 111. RESULTSUSING ACTIVATOR AND OMITTING WETTING AGENT
-Reagent&--
0.05 N
cc.
CO(NO3)z
MgClz
CaClz
BaCL
1 5 1 5 1 5 1
Pb(NOs)z
KAI(SO4)z CUSOl FeClo
5
1 5 1
5 1 5 1 5
AgNOa ZnS04
1 5 1
None
..
5
..
Hz0
cc. 7
3 7
3 7
3
7
3
7
3
7 3 7 3 7 3
7 3 7 3 None S
Mix
Asphalt 1 Medium Medium
Poor Poor Poor Poor
Medium Medium
Very good Very good Very good Very good Very good Very good Good Poor Good Good Very good Very good Very good Very good
30'
45O
60'
1 1 1
1 1 1 1 1
1 1 1 1 1
1 1
1 1 1 1 1 1 1 1
1 1
1 1 1 1
1 1 1
1
1 1 1 1 1
1 1 1 1 1 1 1 1 1
70'
1 1 1 1
1 1 1 1 1 1 1 2 1
3 3 1
1 1
3
..
.. ..
..
..
..
..
Asphalt 2 CaClz
KAl(SO4)z Pb(N0s)z
BaClz AgN08
FeCh CUSO, MgClz Co(N0a)z None
1 5 1 5 1 5 1 5 1 5 1 5 1 5 1 5 1 5
.. ..
7 3 7 3 7 3 7 3 7 3
7
3 7
3 7
3 7 3 8 None
Poor
Poor
Poor
Poor
Poor Poor Poor
Poor Poor Poor
Poor Poor Poor
Good
Poor Poor
Poor Poor
Poor Poor
3 3 3 3 3
I
.
.. ..
..
good mixing when added in very small quantities, but as the quantity was increased the mixing efficiency decreased. However, any particles which were coated in the presence of ferric chloride gave very good adhesion.
Conclusions The ease of covering a sand with a bituminous material by means of simple mixing may be a general indication, but is not a dependable measure of the adhesion relationship between the bitumen and the sand. The best agreement of the mixing test data with those from the wash test occurs where wetting agents are used in conjunction with aluminum, iron, and lead ions-i. e., with those ions which are generally recognized as favorably affecting adhesion of bitumen to aggregate. For such cases and where the aggregate has to be coated in the wet condition with the help of soaptype activators the McLeod test a p pears to have some merit. The mixing test cannot be substituted for the wash test if definite information on the adhesion relationship between bitumen and aggregate is desired. Acknowledgment Thanks are due to F. V. Reagel and R. C. Schappler of the Missouri State Highway Department for permitting the publication of these data. Literature Cited (1) Hubbard, P., Highway Research Board, Proc., 1938,Part I,p. 238. (2) McLeod, N.W.,Assoc. Asphalt Paving Tech., Proc. Tech. Sessions, Dec., 1937, 1-62. (3) Nicholson, V., Ibid., 1932,30. (4)Winterkorn, H. F., Proc. Montana Natl. Bituminous Conf., 1937, 190. ( 5 ) Winterkorn, H. F., Eckert, Geo. W., and Shipley, E. B., Assac.
Asphalt Paving Tech., Proc. Tech. Sessions, Dee., 1937,63.
