Table I1 along with results obtained by a chemical analysis of these emulsions. The agreement between the chemical method and the activation method is considered good. Determination of Iodide in Silver Iodide-Silver Bromide Emulsions. Figure 3 illustrates a series of gamma-ray spectra from the irradiation of the individual elements present in a silver iodide-silver bromide emulsion with 2.8-MeV neutrons. Here again the spectra have been normalized to the same flux, counting time, and weight of sample to facilitate comparison. In the analysis of the samples, the amount of silver present yields an insignificant amount of activity in the region of the iodine peak. The Compton continuum from the 0.51 and 0.62 MeV 60Brpeaks, however, contributes significantly to the iodine peak and therefore must be accurately corrected for. This is done by measuring the g0Br peak at 0.62 MeV using an energy window from 0.58 to 0.67 MeV and multiplying the counts found in this region by a factor which ratios these counts to those in the iodine peak (0.40 to 0.5 MeV) from the irradiation of a pure bromide sample. The calibration curve for iodide is shown in Figure 4. Two determinations, statistically weighted, were used to establish each point on the calibration curve. The error limits shown on the curve are weighted 1u limits and the line is a least squares fit. The error of the slope is less than 0.5 (relative) which is considered excellent for this analysis. Results for the analysis of three silver iodide-silver bromide emulsions are given in Table I1 along with chemical analyses on these same emulsions. It will be noted that the relative standard errors (lu) for both methods overlap for each sample indicating that results by the two methods, for the number of determinations made, are statistically indistinguishable.
Neutron Attenuation and Sample Self-Absorption Effects. It has been well recognized (16) that neutron attenuation and gamma ray self-absorption effects must be corrected for in order to obtain accurate results in neutron activation analysis. With the comparative analytical technique used in these studies, it is important that all points on the calibration line, as well as the sample subsequently analyzed, have approximately the same attenuation. This would permit direct analytical use of the calibration curve without the necessity of correcting for attenuation differences. In order to check whether this was the case for these samples, attenuation factors were calculated for two points on each calibration curve (the lowest and highest points) and for one of the unknown samples for both chlorine and iodine determinations used procedures previously reported (16). The total correction factor was then calculated for two of the points using the lowest point on the calibration line as a reference point. These calculations showed that the maximum error which would result if no attenuation corrections were made is about 0 . 5 z . In all cases in this study, correction for attenuation was neglected without introducing a significant error. ACKNOWLEDGMENT
The authors thank T. Whitely of the Eastman Kodak Research Laboratories for supplying the photographic emulsions used in these studies. They are also indebted to D. Bush and T. Tischer of the Kodak Laboratories for providing chemical analyses on these emulsions. Computational assistance of Sheryl Birkhead of the National Bureau of Standards is gratefully acknowledged. RECEIVED for review November 18,1968. Accepted February 6, 1969.
Effect of Selected Solvents on the Viscosities and Oxygen Contents of Asphalts M. A. Abu-Elgheit,' C. K. Hancock,* and R. N. Traxler Hightvay Research Center, Texas A&M Uniaersity, College Station,Texas 77843 Estimation of the effect of aging, during service, on the properties of asphalts in asphalt-aggregate mixtures is a problem faced by highway engineers. It i s not feasible to measure these properties in situ. Current practice is the solvent extraction of the asphalt from the mixture and subsequent removal of the solvent by distillation. Benzene (a), benzene-ethanol mixture (b), trichloroethylene (c), and l,l,l-trichloroethane (d) were used to determine their effects as solvents on a series of six asphalt cements used in the construction of bituminous pavements. Magnitude of hardening (measured by viscosity at 25 "C) increased in the order (a) through (d). Oxygen content was determined by neutron activation analysis in original and recovered asphalts. In general, the recovered asphalts had lower oxygen contents than the reference asphalts.
ASPHALTSare extracted from mixtures with stone (paving mixtures) for two reasons. First, to determine the amount of asphalt in the mixture and second, to determine changes in consistency and composition of the asphalt that may have occurred during service life in the pavement. In order for this
procedure to be valid, the solvent must not cause a significant change in the consistency or composition (especially the oxygen content) of the asphalt and the recovery from the solution must be carefully conducted to ensure that the asphalt is not markedly hardened by oxidation and over-heating during the recovery process. EXPERIMENTAL
Apparatus. A vacuum rotary thin film evaporator was used to remove the solvents from the extracted asphalts and to protect each recovered bitumen against damage by temperatures above 100 "C (1). 1 Present address, Department of Chemistry, Faculty of Science, Alexandria University, Alexandria, Egypt, U.A.R. Present address, Department of Chemistry, Texas A & M University, College Station, Texas 77843
(1) R. N. Traxler, Proc. Assoc. Asphalt Pacing Technol., 36, 546 (1967). VOL. 41, NO. 6,MAY 1969
823
Table I. Properties of Asphalts Studied
Supplier No. 3 No. 6 No. 11 No. 3 No. 6 No. 11
Grade AC-10 AC-10 AC-10 AC-20 AC-20 AC-20
Viscosity, megapoises, at 77 "F and 5 X 10P sec-1 shear rate 0.75
0.77 1.10 2.10 2.40 2.10
Viscosity, stokes at 140 "F 275 "F 1455 3.70 1235 2.65 1690 3.05 2935 5.10 2735 3.85 3265 3.90
Many of the methods used to measure hardness of asphalts are not very sensitive. Fortunately, a sliding plate, microfilm viscometer has been designed ( 2 ) for obtaining the viscosity, in poises, of paving asphalts over the range of l o 4to lo8 poises. The apparatus has been greatly improved during the past decade and is now available commercially. This instrument was used to measure the viscosities reported below. Its operation and instructions for evaluating the hardening indices of asphalts are described elsewhere (3). Asphalts and Solvents Used. The six asphalts used in this experimental work were obtained from three companies which have been, and are, large suppliers of asphalt for road building in the State of Texas. Two grades (AC-10 and AC-20) of each kind of asphalt were investigated. The term "AC" is an abbreviation for "asphalt cement"; the numbers refer to the viscosities of the materials at 140 OF. The asphalts were made from different crude oils and processed by different procedures. Rheological properties of the six asphalts are shown in Table I. No. 11-30 is a special product which was tested only for oxygen content. When the asphalts are mentioned hereafter in this paper, their source and grade will be separated by a hyphen-e.g., 3-10 represents Asphalt No. 3, grade AC-10. The solvents used in the work described below were: (a) benzene, (b) a mixture of six volumes of benzene with one volume of 95y0 ethanol, (c) trichloroethylene, and (d) l,l,l-trichloroethane. The benzene-ethanol mixture was used to assure nearly complete removal of adsorbed asphaltic components from aggregates that contain some clay. Treatment of Asphalts. ORIGINALASPHALTSDISSOLVED IN UNDRIED SOLVENTS AND RECOVERED BY VACUUM DISTILLATION OF THINFILMS.Each of the first six asphalts used in this study was dissolved in four volumes of each of the four solvents and refluxed for 2 hours. Most of the solvent was distilled off under atmospheric pressure. The concentrated asphalt solution was then distilled in a rotary flash evaporator a t 85-100 "C under vacuum. When all volatile matter was removed from the asphalt, as evidenced by no further change in pressure and no further visible gas release from the hot asphalt (5-8 minutes after the pressure became constant at 20 mm Hg), the molten asphalt was transferred to a small can, desiccated for 2 hours and the friction lid put in place. DRIEDASPHALTSDISSOLVED IN DRIED SOLVENTS AND RECOVERED BY VACUUMDISTILLATION OF THINFILMS.The asphalts and solvents were dried as follows. Approximately 600 grams of each of the six asphalts were placed in a 2-liter round-bottom flask and heated at 120 "C
(2) J. W. A. Labout and W. P. Van Oort, ANAL.CHEM.,28, 1147 (1956). (3) ASTM Staridards Part I I ; Bituminous Materials, Soil: Skid Resistance, p 863 (1968). 824
ANALYTICAL CHEMISTRY
under 20 mm pressure in a rotary flask evaporator. All moisture (and other volatile matter) was removed after about 1.5 hours, but heating was continued for 10 to 15 minutes after the asphalt surface became quiescent. Each hot, dry asphalt was poured into a can and any air present was flushed with nitrogen before applying the friction lid. The closed can was stored in a desiccator. Exposure of the dried asphalts to the atmosphere was kept at a minimum during the removal of samples for testing o r treatment with solvents. Three 1-liter portions of benzene and of trichloroethylene were kept overnight in contact with anhydrous calcium sulfate, "Drierite." After filtering, the solvents were distilled, using a small, simple fractionating column, and the dry solvents were collected (benzene at 79-81 "C and trichloroethylene at 86.6-86.8 "C) after the first 10% of the bulk solvent was distilled over. Each dry solvent was finally passed through a chromatographic column filled with anhydrous alumina and kept in a dark-glass bottle under a nitrogen atmosphere. All viscosities in this study were determined by the thin film, sliding plate viscometer (2) at 25 "C and at a rate of shear of 5 X 10-2 sec-'. Table I1 gives the viscosities of the original six asphalts before and after dissolution and recovery from each of the above mentioned solvents and the hardening indices for each recovered material. Increase in hardness caused by drying the original asphalts are shown in Table 111 together with the viscosity data and hardening indices o n the dried asphalts recovered from dried benzene and from dried trichloroethylene. ANALYSIS FOR OXYGEN
Fast neutron activation analysis for oxygen determinations by a procedure previously reported (4) was used for the measurements given below. Neutron activation analysis has not been widely used in asphalt technology, but the amounts of oxygen, nitrogen, and sulfur in asphalts were measured (5) by this analytical technique. An interesting study on the tracing of oxygen occurrence by fast neutron activation in different asphalts was made (6) and compared with the results obtained by an established chemical method. The oxygen content by the latter method was found to vary from 7.5 to 20001, greater than by the activation method. Neutron activation analysis has also been used (7) to determine oxygen in asphalt, from Wilmington, Calif., and its distillation fractions. In the measurements discussed below, standards were prepared by placing weighed amounts of dry primary standard grade benzoic acid in polyethylene vials. Each vial was then partially filled with hot paraffin wax and carefully stirred with a polyethylene rod until the wax hardened. The exposed portion of the stirring rod was clipped off and discarded and then the vial was sealed. This method of standard preparation was used because it provided a uniform distribution of oxygen throughout a hydrocarbon matrix which resembled the asphalt. Four blanks were prepared using two vials containing paraffin wax and polyethylene rod, and the other two containing only paraffin wax. Effect of Dissolution and Recovery on Viscosities of Asphalts. Undried benzene is the solvent most commonly used in asphalt research laboratories. The hardening indices for the (4) E. L. Steele and W. W. Meinke, ANAL.CHEM., 34, 185 (1962). (5) J. G. Erdman and P. H. Harju, Am. Chem. SOC.Dic. Petroleum Clrem. Preprints, 7 (l), 43 (1962). (6) R . N. Traxler, W. E. Kuykendall, and J. S. Hislop, ANAL. CHEM.,41, 827 (1969). (7) R. V. Helm and J. C. Petersen, ibid., 40, 1100 (1968).
Table 11. Hardening Indices of Undried Asphalts Recovered from Undried Solvents Source and grade of asphalt Condition of asphalt NO. 3-10 NO. 6-10 NO. 11-10 NO. 3-20 NO. 6-20 NO, 11-20 a. Viscosity" of undried asphalt 0.75 0.77 1 .OO 2.10 2.40 2.10 b. Viscosity after recovery from benzene 1 .oo 0.83 1.30 2.60 2.80 2.40 1.15 1.15 H.1.b b/a 1.30 1.10 1.20 1.20 4.00 2.60 1.50 3.40 c. Viscosity after recovery from benzene-ethanol 1.04 0.94 1.65 1.25 1.35 1.60 H.I. c/a 1.40 1.20 2.20 4.25 5.20 4.00 d. Vis. after recovery from trichloroethylene 1.35 1.40 2.20 1.90 2.00 2.00 H.I. d/a 1.80 1.80 5.90 4.80 1.45 1.30 1.80 5.00 e. Vis. after recovery from I,l,l-trichloroethane 2.45 2.30 H.I. e/a 1.90 1.70 1.65 2.40 a All viscosities were measured in megapoises at 25 "C and calculated at 5 X sec-' rate of shear. If the viscosity of the recovered asphalt b Hardening Index (H.I.) is viscosity of recovered asphalt divided by viscosity of original asphalt. is the same as that of the original, the H.I. is 1.00. Table 111. Hardening Indices of Dried Asphalts and Dried Asphalts Recovered from Dried Benzene and Dried Trichloroethylene Source and grade of asphalt Condition of asphalt NO. 3-10 NO. 6-10 NO. 11-10 NO. 3-20 NO. 6-20 NO. 11-20 a. Viscosity" of undried asphalt 0.75 0.77 1.10 2.10 2.40 2.10 2.20 3.20 3.05 0.77 1.10 0.86 f. Viscosity of dried asphalt 1.05 1.30 1.45 H.1.b f/a 1.15 1.00 1.OO Vis. after recovery of dried asphalt from dried g. benzene 1.10 0.85 1.10 2.75 3.40 3.60 H.I. g/f 1.30 1.10 1.OO 1.25 1.05 1.15 h. Vis. after recovery of dried asphalt from dried trichloroethylene 1.45 1.05 1.55 4.05 5.60 5.00 H.I. h/f 1.70 1.40 1.40 1.80 1.75 1.65 a All viscosities were measured in megapoises at 25 "Cand calculated at 5 X 10-2 sec-1 rate of shear. Hardening Index (H.I.)
Asphalt condition 1. Undried original Recovered from: (a) Benzene (b) Benzene-ethanol (c) Trichloroethylene (d) 1,I ,1-Trichloroethane 2. Dried original Recovered from: (e) Dried benzene (f) Dried trichloroethylene Accurate to =tO.Ol%.
Table IV. Per Cent Oxygen in Asphalts Tested Percentage of oxygen by w t a NO. 3-10 NO. 6-10 NO, 11-10 NO. 3-20 NO. 6-20 0.34 0.71 0.93 0.33 0.67
NO. 11-20
NO. 11-30
0.87
1.15
0.32 0.28 0.26 0.29 0.26
0.66 0.65 0.62 0.66 0.65
0.88 0.71 0.83 0.77 0.80
0.32 0.31 0.28 0.25 0.27
0.61 0.65 0.59 0.74 0.67
0.65 0.83 0.78 0.90 0.81
0.93 0.88 0.95 0.99 1.04
0.34 0.23
0.71 0.62
0.90
0.35 0.23
0.78 0.65
0.93
0.78
0.80
1.28 0.97
six undried asphalts recovered from this solvent, Table 11, are within the range of 1.10 to 1.30, which is quite satisfactory (close to 1.00). Dissolution in and recovery from the benzene-ethanol mixture resulted in slightly higher hardening indices of 1.20 to 1.65 for the six recovered asphalts. The hardening indices for the six undried asphalts recovered from undried trichloroethylene ranged from 1.80 to 2.20. These indices are considerably higher than those obtained from the use of benzene o r the benzene-ethanol mixture and are undesirably high. l,l,l-Trichloroethane is used by some laboratories to extract asphalt from a pavement sample to determine the amount of asphalt present, but is generally not used when it is necessary to recover and test the asphalt. This is confirmed by the data in Table I1 which show that the hardening indices
ranging from 1.65 to 2.45 for the six asphalts recovered from l,l,l-trichloroethane are the highest of all of the hardening indices recorded in that table. Table I11 shows that drying the original asphalts resulted i n hardening indices of 1.00 to 1.45. Dried asphalts after dissolution in and recovery from dried benzene gave low hardening indices ranging from 1.OO to 1.30. Hardening indices f o r the dried asphalts recovered from dried trichloroethylene were 1.40 to 1.80. Effect of Dissolution and Recovery on Oxygen Content of Asphalts. Table IV indicates that the original AC-10 grade asphalts have a slightly higher percentage of oxygen than t h e original AC-20 grade asphalts. Asphalt No. 3 has t h e lowest, No. 6 the intermediate, and No. 11 the highest oxygen content. VOL. 41, NO. 6, MAY 1969
825
Table V.
Oxygen in Dried Trichloroethylene Recovered from Dried Asphalts Neutron Oxygen counts counts Oxygen Asphalt average PSDa average wt, mg NO. 3-10 25227 258 14.8 0.70 NO. 6-10 26486 254 4.6 0.70 NO. 11-10 26195 279 6.5 0.80 NO. 3-20 26258 172 16.3 0.55 NO. 6-20 26137 203 4.2 0.60 NO. 11-20 26024 198 6.3 0.60 NO. 11-30 25949 248 5.0 0.70 a Per cent standard deviation. Table VI.
Corrected Per Cent Oxygen in Dried Asphalts Recovered from Dried Trichloroethylene Asphalt Oxygen, %" NO.3-10 0.23 NO,6-10 0.62 NO. 11-10 0.78
NO. 3-20 NO, 6-20 NO. 11-20 NO. 11-30 a Average of two determinations.
0.23 0.65 0.80 0.97
For the all undried asphalts and solvents, except No. 6-20 and No. 11-20 from 1,1,1-trichloroethane, the recovered asphalts showed a lower percentage of oxygen than the original asphalts. Dissolution and recovery of asphalts from benzene resulted in a higher oxygen content in the AC-IO grades than in the AC-20 of asphalts 6 and 11. The oxygen contents of the two grades of Asphalt No. 3, however, are the same. The AC-10 grade of asphalts No. 3 and No. 11 recovered from the benzene-ethanol mixture were found to contain less oxygen than the AC-20 grades under the same conditions. Again, the two grades of Asphalt No. 6 had the same oxygen content. I t had been anticipated that the asphalts recovered from the benzene-ethanol mixture would contain more oxygen than the original or the material recovered from benzene. This was true, however, for only No. 6-20 and NO.11-20. Of the asphalts recovered from trichloroethylene, the AC-10 grades have a higher percentage of oxygen than the AC-20 grades, except for Asphalt No. 3 where the reverse is true. Both grades of No. 3 and No. 6 recovered from trichloroethylene have lower oxygen contents than the same grades recovered from benzene. The AC-IO grade asphalts recovered from l,l,l-trichloroethane contain less oxygen than the AC-20 grades, with the exception of No. 3-10 which contains more oxygen than No. 3-20. For No. 11-30, the highest oxygen content was found in the original asphalt, and the lowest in the asphalt recovered from benzene-ethanol solution. The oxygen contents of the recovered asphalt from the other three undried solvents are intermediate. For the original dried asphalts, it was found that the AC-10 grades have slightly lower oxygen contents than the AC-20
826
ANALYTICAL CHEMISTRY
grades. This may be caused by a larger amount of moisture and Cor being dissolved in the undried AC-10 than in the undried AC-20 grades. The amounts of oxygen in the dried asphalts recovered from the dried solvents are higher than in the dried original asphalts. This increase in oxygen content may be caused by contamination of the solvents during the process of drying. Samples of dried benzene, undried benzene, dried trichloroethylene, and undried trichloroethylene were analyzed for oxygen by the same method used for the asphalts. The vials in this case were filled with the solvent to the average volume occupied by the various asphalts. This was taken as approximately 7570 of the vial volume (0.8 ml). The amounts of oxygen in these solvents were found to be 0.4, 0.4, 1.8, and 0.9 mg, respectively. While the oxygen content of dried benzene remained unchanged, it was doubled in dried trichloroethylene. Based on this observation, the dried trichloroethylene recovered from the dried asphalts was analyzed, and the amount of oxygen in each portion of recovered solvent is given in Table V. The amount of oxygen in each asphalt due to contamination from the solvent was taken as the difference between the amount of oxygen in the dried solvent before and after recovery. These amounts were then subtracted from the weights of oxygen found in dried asphalts recovered from dried trichloroethylene. After this correction, the per cent oxygen in the seven recovered asphalts was estimated and recorded in Table VI. These corrected values show that the dissolution and recovery of dried asphalts from dried trichloroethylene resulted in a lower oxygen content than of the original dried asphalts. Inasmuch as no difference in oxygen content of dried and undried benzene has been detected by activation analysis, the higher per cent oxygen in the recovered dried asphalts from dried benzene over that in the dry originals is, at present, unexplainable. Finally, the oxygen contents of the different asphalts recovered from the undried asphalt-solvent combinations (see Table IV) show that the lowest oxygen contents were obtained under Condition (a)-No. Condition (b)-No. Condition (c)-No. Condition (d)-No.
11-20 11-10 and No. 11-30 3-10, No. 6-10, and No. 6-20 3-20
It is interesting that the difference in oxygen content between the lowest and original values is the same for the AC-IO and AC-20 grades of each asphalt. This difference was found to be 0.08% for Asphalt No. 3, 0.08-0.09% for Asphalt No. 6 and 0.227& for Asphalt No. 11. The airblown grade, Asphalt No. 11-30 shows a difference of 0.27%. The corresponding data on the dried asphalt-solvent systems showed some variations. ACKNOWLEDGMENT
The authors are greatly indebted to W. E. Kuykendall for his help and advice concerning the activation analysis. RECEIVED for review October 23, 1968. Accepted March 13, 1969. The early stages of this study were supported in part by a research grant from the Robert A. Welch Foundation.
