polyphosphoric acid modified asphalt: proposed … professor, physical chemistry, henderson state...

Polyphosphoric Acid Modified Asphalt: Proposed Mechanisms

Gaylon L. Baumgardner1, J-F. Masson2, John R. Hardee3,

Andy M. Menapace4, Austin G. Williams5

Abstract

Asphalt binders have been chemically modified with polyphosphoric acid (PPA) to improve high temperature rheological properties without adversely affecting low temperature rheological properties since the early 1970’s. More recently, PPA has been used in Superpave performance-grade (PG) binders that need an extended range between the high and low temperature performance requirements. The mechanism of chemical modification of asphalt with PPA remains in great part unknown. This paper presents results that will help to better understand the mechanisms of chemical modification with PPA. PPA modified and unmodified asphalts from different crude sources were analyzed for chemical composition by asphaltene precipitation, thin-layer chromatography (TLC) and nuclear magnetic resonance (NMR), by gel-permeation chromatography (GPC) and atomic force microscopy (AFM). The results indicate that the mechanism of PPA action depends on the base asphalt. In one case PPA affected a phase dispersed in asphalt, in the other case it affected the asphalt matrix. In both cases, PPA caused stiffening of the modified phase. Several stiffening mechanisms are proposed.

Key Words: Polyphosphoric acid, modified asphalt, chromatography, friction microscopy, reaction mechanisms

1 Executive Vice President, Paragon Technical Services, Inc. [email protected] 2 Senior Research Officer, National Research Council of Canada [email protected] 3 Professor, Physical Chemistry, Henderson State University [email protected] 4 Group Leader, Asphalt, Paragon Technical Services, Inc. [email protected] 5 Research Technician, Asphalt, Paragon Technical Services, Inc. [email protected] The oral presentation was made by Mr. Baumgardner

Introduction and Background

US Patent number 3,751,278 issued August 7, 1973 describes a “Method of Treating Asphalt.” In summary, the object of the invention was to provide a method to alter the viscosity- penetration relationship of an asphalt. More specifically, the object was to substantially increase the high temperature characteristics of asphalt, in particular high temperature viscosity and softening point, without significantly decreasing the 25 C penetration of the asphalt. Another object was to provide an asphalt composition with unique temperature susceptibility characteristics (1). In the method, mixtures of condensed derivatives of phosphoric acid (H3PO4) with P2O5 equivalents of greater than 100% were used to modify asphalt binders.

In the 1970’s viscosity was the method used to grade asphalt binders. Some states specified viscosity grades, in particular AC-40, in accordance with then current AASHTO guidelines, with additional requirements for minimum penetration values. These binders were specified in an attempt to obtain binders that would resist rutting while providing good performance against thermal cracking. While the concept was good, these binders were difficult to produce from conventional refining methods; therefore, super phosphoric acid was employed to increase the viscosity of a standard AC-30 to that of an AC-40 minimally effecting the binder penetration.

More recently, with the advent of Superpave and the application of performance grading (PG), it has been assumed that the performance requirements for large loads, or slow traffic could be met by an increase in the higher temperature of the performance grade. For example, standard grade PG 64-22 for normal traffic, could be shifted to PG 70-22 for slower heavy traffic and to PG 76-22 for heavy standing or interstate conditions. Upon these modifications, the grades would respectively span 86C°, 92C° and 98C° of performance. Typically, performance grades that span more than 90C° require asphalt modification. While polymer modification has been the more common, polyphosphoric acid (PPA) modification can also be used, the advantage being that it improves the high temperature rheological properties without affecting the low temperature grade.

Baumgardner, Masson, Hardee, Manapace, Williams

The use of PPA modified binders is often debated, to the point some agencies have banned the use of acid modified binders. Such actions result from a lack of understanding of the benefits of PPA as a tool to improve the performance of asphalt binders, combined with a lack of understanding of the mechanisms of the action of PPA. In an effort to better understand this mechanism, modified and unmodified asphalts from two crude sources were analyzed for chemical composition by asphaltenes precipitation thin-layer chromatography (TLC) and nuclear magnetic resonance (NMR), and by gel-permeation chromatography (GPC) and atomic force microscopy (AFM).

Experimental

Binder Formulations Asphalt from Saudi and Venezuelan (Venz) crude sources with

respective grades of PG 64-22 and PG 67-22 were modified with PPA to PG 70-22 (Table 1). Just enough PPA was added to the original asphalt binder to achieve PG 70-22. This was 1.2 percent and 0.62 percent by wt of binder for the respective Saudi and Venezuelan binders.

Table 1. Asphalt Identification and Characteristics Asphalt PG True PG Comment Saudi 64-22 67.6-23.5 Control sample Saudi Modified 70-22 72.25-25.1 PPA modified Saudi Venz 67-22 68.5-24.0 Control sample Venz Modified 70-22 71.6-25.4 PPA modified Venz

Asphalt Composition

Each binder was deasphaltened according to ASTM Method D-3279 “Standard Test Method for n-heptane Insolubles” to yield asphaltenes (As) and maltenes which is the n-heptane soluble portion.

The maltenes were further fractionated on an Iatroscan TH-10 Hydrocarbon Analyzer to yield the composition in saturates (S), cyclics (C) and resins (R). The method has been described in

Polyphosphoric Acid

detail before (2, 3). N-pentane was used to elute saturates, and a 90/10 toluene/chloroform solution was used to elute cyclics. The resins were not eluted and remained at the origin. The reported Iatroscan results are averages of ten analyses.

Nuclear magnetic resonance (NMR) analysis was performed on the asphaltene and maltene fractions of each asphalt. Asphaltene and maltene fractions were obtained as described above. Phosphorus-31 NMR experiments were carried out on a Bruker 200 MHz instrument. The spectra of asphaltenes were obtained on samples containing 0.1 g of asphaltenes dissolved in 1 ml of deuterated chloroform CDCl3.The spectra for maltenes were obtained on samples containing 0.2 ml of CDCl3 dissolved in 1 ml of maltenes. The spectrum width was 350 ppm and 1024 scans were obtained on each sample.

Gel-permeation Chromatography

Gel-permeation chromatography (GPC) was performed on the asphaltenes. GPC was performed on a Hewlett-Packard 1050 HPLC. A TSK-GELRG4000HHR column and a TSK-GELRG3000 column were used in series. An HXLL2 guard column was placed in line before the two GELR colum

Atomic Force Microscopy Binders were prepared for atomic force microscopy by the

application of a small bead of asphalt to a steel stub. With a knife, the bead was scraped against the surface of the stub and the film heated to 115 C for about 2 min to allow the film surface to level.

Atomic force microscopy (AFM) images were captured at room temperature on a JEOL JSPM-5200 microscope. Both


ns. Five one hundredths of a gram (0.05 g) of asphaltenes were dissolved in 5 ml of tetrahydrofuran (THF) and then stirred with a magnetic stirrer for 30 minutes. The resulting solution was passed through a 0.45 µ filter. Analysis was performed on a 25 µl injection, using THF as the solvent at a flow rate of 1 ml/min. The columns were maintained at a temperature of 35 C and a refractive index (RI) detector was used. Reported weight average molecular weights are polystyrene (PS) equivalents obtained from the analysis of PS standards with weight average molecular weights between 50,000 g/mol and 4130 g/mol.

films had been annealed 72 h to 96 h at room temperature. The silicon AFM probes (MikroMasch, Tallinn, Estonia) had a stiffness of 40 N/m. The basics of AFM and the origin of the topographic and friction signals were described before (4,5,6). The topographic images reveal vertical elevations and declinations associated with surface features, whereas the friction image allows for the differentiation of surface material based on changes in elastic or adhesive properties. It thus reveals changes in surface composition, without revealing the nature of the change. All the microphotographs show a 15 µm x 15 µm region unless otherwise indicated.

Results Asphaltenes precipitation and TLC maltenes fractionation data

are presented in Table 2. Modification of the Saudi asphalt binder with 1.2 wt. percent PPA increased asphaltenes content from 9.1 wt. percent to 14.7 wt. percent to produce the modified Saudi PG 70-22. Similarly, modification of the Venezuelan asphalt with 0.62 wt. percent PPA increased asphaltenes from 10.5 wt. percent to 14.9 wt. percent to produce the modified Venezuelan PG 70-22.

Table 2. Asphalt Composition

Asphalt A R C S Saudi 64-22 9.1 11.2 75.5 4.4 Saudi Modified 70-22 14.7 10.5 74.4 0.4 Venz 67-22 10.5 21.5 65.2 2.8 Venz Modified 70-22 14.9 15.2 63.1 6.8

Further analysis of precipitated asphaltenes using P-31 nuclear

magnetic resonance (NMR) revealed no phosphorous compounds in the asphaltenes fraction of the non-modified asphalt binders, while phosphorous compounds were present in the precipitated asphaltenes from the PPA modified asphalt binders. P-31 NMR of the maltenes fractions from the non-modified and PPA modified asphalt binders revealed no phosphorous compounds. NMR

Polyphosphoric Acid

topographic and friction images were obtained after the asphalt

results support that PPA preferentially reacts with the asphaltenic phase of the asphalt as proposed by G. Orange et al. (7).

The AFM friction image for unmodified Saudi asphalt is shown in Figure 1. This asphalt shows two separate domains, a homogeneous matrix and flake-like domains dispersed in that matrix. The flakes are numerous and nearly form a co-continuous phase. The average size of the flakes is about 1 µm. The topographic image was monotonous and indicated that the surface was flat (not shown).

Figure 1. Phase Image of the Saudi Asphalt on a Scale of 15 µm x 15 µm.

The GPC trace for asphaltenes precipitated from the Saudi binder is shown in Figure 2 and Table 3. It reveals a maximum around 15 minutes of elution, which corresponds to a weight average molecular weight of 5200 g/mol. On the right of this maximum appears a broad shoulder for lower molecular weight material. The shoulder was centered near 1200 g/mol.


-5

0

5

10

15

20

25

10 12 14 16 18 20 22

Time/minutes (Increasing Molecular Weight Right to Left)

RI R

espo

nse

SaudiSaudi Modified

Figure 2. GPC Results for Precipitated Asphaltenes from Saudi and Saudi Modified Asphalts

Table 3. Saudi and PPA Modified Saudi Asphaltene

Molecular Weight and Molecular Weight Distribution

Asphalt Molecular Weight Molecular Weight Range

at Maximum at Half Height

Saudi 5200 g/mol 11,000 to 300 g/mol

Saudi Modified 1200 g/mol 7,300 to 170 g/mol The microstructure of the Saudi asphalt was affected by PPA,

Figure 3. Ovoid domains about 2 µm on the long side were then dispersed in a homogeneous matrix. These domains were larger, but less numerous than the flake-like domains in the original binder, and at the center of each domain was a small bee-like structure reminiscent of those observed by Pauli et al.(8). The topographic image (not shown) indicated that the dispersed phase protruded very slightly from the matrix surface and that the bee-like centers were higher still and somewhat more visible.

Polyphosphoric Acid

Figure 3. Phase Image of PPA Modified Saudi Asphalt PPA modification of the Saudi asphalt binder affected its

molecular weight profile (Figure 2). The high molecular weight peak disappeared completely and only the original shoulder with a maximum at 1200 g/mol remained. The PPA modification also led to changes in the chemical composition of the binder as shown in Table 2, with the most important change being an apparent conversion of saturates into asphaltenes.

The friction image for the unmodified Venezuelan asphalt binder is shown in Figure 4. It showed small domains dispersed in a homogeneous matrix. The average size of these domains was about 0.6 µm. The topographic image was void of any features and not shown. The GPC result showed a unimodal molecular eight distribution that indicated an average molecular weight of 2100 g/mol, Figure 5.


Figure 4. Phase Image of the Venezuelan Asphalt on a Scale of 15 µm x 15 µm.

-5

0

5

10

15

20

25

10 12 14 16 18 20 22

Time/minutes (Increasing Molecular Weight Right to Left)

RI R

espo

nse

VenzVenz Modified

Figure 5. GPC Results for Precipitated Asphaltenes from Venezuelan and PPA Modified Venezuelan Asphalts

Polyphosphoric Acid

Table 4. Venezuelan and PPA Modified Venezuelan Asphaltene Molecular Weight and Molecular Weight

Distribution

Asphalt Molecular Weight Molecular Weight Range

at Maximum at Half Height

Venz 2100 11,000 to 160

Venz Modified 1700 7,300 to 140

Upon modification of the Venezuelan asphalt binder with PPA, the dispersed phase remained unaffected, but its contrast with the matrix was reduced, Figure 6, and the matrix was no longer homogeneous, which was better seen at higher magnification, Figure 7. The asphalt matrix in the PPA modified Venezuelan asphalt binder was peppered with very fine domains of about 60 nm (0.06 µm) in size and contained narrow strings of matter up to about 1.5 µm long.

Figure 6. Phase Images of the PPA Modified Venezuelan Asphalt on a 15 µm x 15 µm


Figure 7. Phase Images of the PPA Modified Venezuelan Asphalt on a 5 µm x 5 µm Scale

The effect of PPA modification on the Venezuelan binder was to reduce the average molecular weight slightly from 2100 g/mol to 1700 g/mol, Figure 5 and Table 4, and to change the chemical composition. It raised both the asphaltenes and saturates contents, at the expense of the cyclics and resins (Table 2).

Discussion

The AFM friction image arises from changes in composition and stiffness across a sample surface. The greater the contrast between the domains in the friction image, the greater is the difference in stiffness and composition. Figure 1 shows that the Saudi binder had two phases of different composition, which is in agreement with the bimodal molecular weight distribution obtained by GPC. Upon PPA modification of the Saudi asphalt, the contrast between the matrix and the dispersed domains was increased as seen in a comparison of Figures 1 and 3. Either the dispersed phase became stiffer or the matrix became softer, or both. This may be explained by a chemico-physical process where PPA first reacts with bitumen, followed by the segregation of polar material

Polyphosphoric Acid

out of a non-polar matrix, the reordering leading to domains with sharp boundaries. In accordance with the phase contrasts, the modified matrix would be softer and more adhesive than in the unmodified binder, whereas the dispersed phase would be stiffer and less adhesive, the stiffer phase leading to the rise in PG.

The proposed chemico-physical process does not address the nature of the reaction between PPA and the binder. Orange et al. (7) hypothesized that PPA protonates basic sites, which induces a loss of hydrogen bonding and the disaggregation of asphaltenes, with the result being a greater dispersion of smaller asphaltene domains. Based on GPC (Figure 2), it could be assumed that PPA disperses associated asphaltenes into smaller domains in solution. With the binders under consideration here, the script must be incomplete, however, as Figures 1 and 3 do not indicate dispersion, but a greater association of polar material. Moreover, a simple dispersion disregards the increase in asphaltenes and the fall in saturates (Table 2). Other mechanisms must also be at play.

The changes in the Saudi binder may be the result of a series of chemical reactions as illustrated in Table 5. The acidolysis of alkyl-aromatics (scenario A) would explain both the reduction in asphaltenes molecular weight and the greater dispersion of smaller asphaltenes. The PPA-adduct would also be consistent with the presence of phosphorus in the asphaltenes as obtained by 31P NMR. Scenario B, which also leads to polar PPA adduct, would explain the loss of saturates and the increase in the size of the associated polar domains in Figure 3 through the association of all the PPA containing material. The increase in asphaltenes (heptane insolubles) may then result from the co-precipitation of asphaltenes with polar and insoluble PPA-adducts. These two scenarios are not entirely satisfactory, however, as PPA adduct would contain C-O-P bonds that have not been detected in asphaltenes (7). The co-precipitation of a physical mixture of asphaltenes and neat PPA, rather than adducts, could also explain the presence of phosphorus in asphaltenes.


Table 5. Possible Mechanisms of PPA Reaction with the Saudi Binder

Table 5 also shows scenarios C and D, which represent the alkylation of aromatic rings. These reactions could explain the increase in asphaltenes and the loss of saturates through coupling reactions.

The Venezuelan binder initially showed a fine dispersion in a continuous matrix. Interestingly, the GPC results did not reflect a

Polyphosphoric Acid

A. Acidolysis of alkyl-aromatics and nucleophilic displacement

polar + less polar

X

R

XH+

R

PPA- PPA

+ HX R

X= N, O, S

H+

B. PPA mediated nucleophilic displacement in saturates R S

R1

H+

R SH+

R1

PPA-

R PPA SHR1

+ C. Alkylation of aromatics with sulfides, alcohols

+H

+

R1

R2

-H2X

R1

R2

XH R1

R2

XH 2+

R1

CH+

R2

X= S, O

D. Alkylation of aromatics with alkenes

R1

R2

CH3

+H

+

R1 C+

R2

CH3

-H+

R2

CH3

R1

biphasic system and did not provide a bimodal molecular weight distribution similar to that of the Saudi binder. The GPC showed a unimodal molecular weight distribution, which indicates that the possible ordering of matter in solution (GPC) does not necessarily reflect the initial solid-state arrangement. For example, semi-crystalline matter shows separate phases in the solid-state but not in solution.

Upon PPA modification of the Venezuelan asphalt binder, the contrast between the matrix and the dispersed phase decreased, Figures 4 and 6. Hence, PPA reduced the difference in stiffness between the phases. Given the modification of the matrix of this asphalt binder, Figure 6, and the likelihood of a PPA acidification of the binder, it is reasonable to assume that the asphalt matrix increased in stiffness and that the dispersed phase was already relatively stiff. Given the low saturates content, the area of the dispersed phase in Figures 6 and 7, and the unimodal GPC distribution mentioned above, the dispersed phase was likely stiff semi-crystalline paraffinic and un-reactive material. The original matrix was more likely amorphous, more polar and more reactive with PPA. The result is a stiffer phase with a higher PG (Table 1). Soon to be published AFM and modulated DSC work on a series of asphalts confirm that discrete paraffinic material can be dispersed in the asphalt matrix.

At least two scenarios may concur to increase the stiffness of the continuous phase in the Venezuelan binder. First is the cross-linking of reactive segments to form a matrix of covalently linked matter., i.e., asphalt-PPA-asphalt, with un-reacted or elongated domains of PPA chains being responsible for the observed strings (Figure 7); Second, is the PPA catalyzed cyclization of alkyl aromatics (9), which would lead to stiffer naphthene aromatics as illustrated by scenarios E and F in Table 6. Further stiffening of the binder could be obtained from phosphate salts that aggregate and form ionic clusters as in ionic polymers (10). This is illustrated by scenario G in Table 6. The ionic clusters are stiff and provide thermo-reversible cross-links. These clusters might explain the development of the very fine 60 nm dispersion.


Table 6. Possible Mechanisms of PPA Reaction with the Venezuelan Binder

Scenarios E to G do not explain the increase in saturates in the Venezuelan binder after PPA modification. An acidolysis of the pendant alkyl chains on aromatic nuclei, illustrated in scenario A for the Saudi binder in Table 5, would be consistent with this increase as a side chain is freed from an aromatic ring and increases the saturates content. The breaking of alkyl aromatics in resins and asphaltenes into alkyl and stiff aromatic fragments would further explain the increase in n-heptane precipitates, the presence of phosphorus in asphaltenes (as per 31P NMR), and the segregation and formation of the additional domains.

Hence, a number of possible reactions between PPA and asphalts obviously exist. No single reaction is satisfactory by itself

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E. Cyclization of carboxylic acids H

+

-H2O

O

OH

O

F. Cyclization of alcohols

HO

H +

H 2O+

-H 2O

G. Formation of an amino-phosphate salt and ionic cluster

PPA-H

NH

R

NH2

+

R

PPA-

Ion pair

N ion pairs

-++-

-

--+++

+ Cluster: Ionic nucleus +

non-ionic hydrocarbon shell

and given the multiplicity of functional groups in asphalts, various competing reactions most likely occur as illustrated here. The importance of any reaction will be determined by the composition of the asphalt.

Conclusion

Two asphalts were modified with PPA and the resulting change in microstructure and composition was investigated by AFM, GPC and chemical analysis. The performance grade of both asphalts was raised by PPA, which was observed in AFM as a stiffening of one of the two main phases in asphalt. In one asphalt, PPA affected the dispersed phase; in the other, it affected the matrix. The stiffening effect of PPA was thus asphalt dependent.

Several mechanisms were proposed to explain the stiffening from the PPA modification of asphalt binders: formation of PPA adducts; alkylation of aromatics; cross-linking of neighboring asphalt segments; the formation of ionic clusters; and the cyclization of alkyl aromatics. Detailed physico-chemical analysis of PPA-modified asphalt binders will be required to determine which mechanism(s) prevail. Acknowledgement

JFM wishes to thank Ms Valérie Leblond for the capture of the AFM images.

References 1. Stephen H. Alexander, United States Patent 3,751,278 Aug. 7, 1973,

“Method of Treating Asphalt” 2. J-F. Masson, T. Price, and P. Collins, “Dynamics of Bitumen Fractions by

Thin-Layer Chromatography/Flame Ionization Detection”, Energy & Fuels 2001, 15, 955-960.

3 L. Raki, J-F. Masson, P. Collins, “Rapid Bulk Fractionation of Maltenes into Saturates, Aromatics and Resins by Flash Chromatography”, Energy & Fuels 2000, 14, 160-163.

4. R. M. Overney, E. Meyer, J. Frommer, D. Brodbeck, R. Lüthi, L. Howald, H.-J. Güntherodt, M. Fujihira, H. Takano, and Y. Gotoh, “Friction Measurements on Phase-Separated Thin Films with a Modified Atomic Force Microscope”, Nature, 1992, 359, 133-135.


5. E. zer Muhlen and H. Niehus, “Introduction to Atomic Force Microscopy and its Application to the Study of Lipid Nanoparticles”, Chapter 7 in Particle and Surface Characterization Methods, R. H. Muller and W. Mehnert Eds, Medpharm Scientific Pub, Stuttgart, 1997.

6. H. Takano, J.R. Kenseth, S.-S. Wong, J.C. O’Brien, M.D. Porter, “Chemical and Biochemical Analysis Using Scanning Force Microscopy”, Chemical Reviews 1999, 99, 2845-2890.

7. G. Orange, D. Dupuis, J. V. Marin, F. Farcas, C. Such, B. Marcant, “Chemical Modification of Bitumen through Polyphosphoric Acid: Properties-Microstructure Relationship”, 3rd Euraphalt & Eurobitume Congress, Vienna, 2004. Paper 334, book 1, p. 733-745.

8. A. T. Pauli, J. F. Branthaver, R. E. Robertson, W. Grimes, C. M. Eggleston, “Atomic Force Microscopy Investigation of SHRP Asphalts, Symposium on Heavy Oils and Resid Compatibility and Stability”, American Chemical Society, Division of Petroleum Chemistry, San Diego, CA, April 1-5, 2001, pp. 104-110.

9. F. A Carey and R. J. Sunberg, Advanced Organic Chemistry, Part B: Reactions and Synthesis. Plenum Press, New York, 2nd Ed. 1983, p. 386.

10. A. Eisenberg and J.-S. Kim, Introduction to Ionomers. Wiley-Intescience, New York, 1998.

Discussions

DOCTOR ROBERT KLUTTZ – You’re just looking at the asphaltenes? MR. BAUMGARDNER – No we are looking at asphaltene and maltene. Basically we dissolved the asphaltenes in duterated chloroform , I can’t remember what the concentration was. We did the same the maltene, however, you really don’t dissolve the maltene, we added duterated chloroform to the maltene fraction that’s how we ran them in the NMR. DR. KLUTTZ – But you’re getting enough resolution in the NMR that if you go back and do some detailed analysis you can probably pick that out? MR. BAUMGARDNER – Yes. DR. KLUTTZ – Okay, that sounds great. On the GPC, you might have said but I missed it – what’s the pore size on the columns?

Polyphosphoric Acid

MR. BAUMGARDNER – You know I called to find that out today because I’m used to using styrogel columns from – I can’t remember who – and these were Supelco columns. It was a G5000, I mean G4000 and a G3000, I’m not sure what the pore size was.

MR. BAUMGARDNER – What excited us was the correlation between the micrographs and the GPC curve that you can see the differences anyway. DR. KLUTTZ – Really nifty work. MR. ROBERT DUNNING – Just a comment about using OP205 or phosphoric acid. This has been used… MR. BAUMGARDNER – I’m going to stop you – it’s not P205 it’s poly-phosphoric acid. MR. DUNNING – I understand, but those both have been used to do the same thing in air blowing and to make membrane asphalts like with a 200 softening point and a 50 pen for example. These materials have been used as you know for many, many years. One characteristic, however, is they tend to slip. In other words, they’ll hold pen and drop softening point which shows perhaps some instability with the bonding that could change. MR. BAUMGARDNER – We’ve actually done considerable – I’ve said there were several papers. We’ve actually done considerable work on the aging of poly-phosphoric acid modified looking at rheology and looking and we didn’t see any of that.


DR. KLUTTZ – I don’t know what those mean, but just looking at the peaks it looks like you may be getting some truncation on the high molecular weight end so it might be interesting to go back and look with a larger pore size column and see if you get some more information there. It’s dead flat then all of a sudden it takes off, that’s pretty unusual behavior. So you may have some more structure in there.

MR. DUNNING – Well I do know it happens in the industry; that they do slip and have to be touched up in an air blow.

MR. BAUMGARDNER – What we’ve seen Jim with the lime is it’s not a great effect as far as it doesn’t neutralize the lime. We’ve actually seen that the lime makes it so stiff that any reversal of the reaction, if you want to call it that, is null and void because the lime does enough stiffening on its own of the binder. Basically though, that’s why I said, use it properly and formulate properly if you are using anti-strips or lime or whatever. It’s up to the supplier to make sure he’s not going to have problems with you know, reversing the reaction or the stiffness of the binder. MR. SCHEROCMAN – But I am not sure the supplier ever tells the contractor that he has acid modified the materials. How does the contractor really know? MR. BAUMGARDNER – If he’s using lime I’m not as concerned about it as using liquid anti-strips. MR. VYT PUZINAUSKAS – In Bob Dunning’s question, where he mentioned P205, blown materials and you mentioned, you said this is different, this is poly-phosphoric acid other than ortho phosphoric acid. What are the differences? MR. BAUMGARDNER – Poly-phosphoric acid, like 105% is expressed as the equivalent of P205 but there’s not necessarily, it’s not necessarily P205 as we know P205. It’s expressed as a percentage equivalent of P205 as poly-phosphoric acid. P205 and poly-phosphoric acid are two different compounds.

Polyphosphoric Acid

your paper, but I have no clue what you said so I just have a dumb question to ask. If I add hydrated lime to a mix, and I have the acid modified binder, what effect does the presence of the acid and the concentration of the acid have on the lime as far as anti-stripping effectiveness goes? Does it create a problem by neutralizing the lime?

MR. JIM SCHEROCMAN – I would like to make a comment on

MR. PUZINAUSKAS – Right, but, are you familiar with the work done by Arnold Hiberg? MR. BAUMGARDNER – Yes, very familiar with it. MR. PUZINAUSKAS – P205 catalyzed material for hydraulic applications and so, this is no similarity to that? Mechanisms would be different? MR. BAUMGARDNER – Mechanisms are similar, that’s where some of the information I am giving is from is Arnold Hiberg. MR. PUZINAUSKAS – Are you also aware that these phosphoric acids have been used by dentists in presence of silicas the fillings in teeth? (Yes.) So maybe this is, you’re shooting with one bullet two rabbits. You put the phosphoric acid compounds there in soils and minerals where silica will produce some kind of superior binders. MR. BAUMGARDNER – Good point. DR. GERALD REINKE – The issue with regard to softening point fall back with oxidized materials only occurs when you heat that material back up to or above the blowing temperature. As far as modified material, PG you know 58-34, 64-28, and so forth, we’ve held tanks of this material all summer and it has not dropped the SR stiffness nor has it increased while as you would expect if the material was aging artificially. So whatever is going on in fall back with oxidized material is certainly not something we see going on in the real world with PG graded materials.

MR. JEAN-VALERY MARTIN – Just to comment, a few words about the difference of P205 and poly-phosphoric acid. Poly-phosphoric acid is an inorganic acid. It came from the desiccation of the auto-phosphoric acid which is the industry P04. So there is


MR. BAUMGARDNER – Good comment Jerry. That’s why I said we didn’t see it in the aging we had done on the modified non-blown materials.

nothing linked with the P205. P205 is a solid form. We usually in this field express as a P205 content, but this is not the real species inside this liquid. It’s a blending of different inorganic polymer with different chain links. Except that – excellent presentation. MR. TERRY ARNOLD – Gaylon, you and I have talked about this. I don’t think – have you done anything with water solubility? You see an increase in heptane insolubles after treatment with phosphoric acid. Have you done anything to see if that increase diminishes after water washing of the asphalt? Phosphates generally are very water-soluble. MR. BAUMGARDNER – What we did Terry, this is in the paper we submitted to the Journal of Analytical Chemistry, looking at a method called Solid Phase Micro Extraction using SPME Fibers and GC mass spec. We found that when we did a water wash similar to what Dr. Gayle King and Dr. Safwat Bishara had done on the asphalt toluene solution, we did find phosphorous compounds in the water solution, but when we added, for example, amines or lime to the asphalt before extraction, we did not find phosphorus or amines in the extracted water solution. So if that’s what you’re talking about, I’m not positive but we did do some work on that, but more or less looking at the method using the SPME analysis. MR. TERRY ARNOLD – We’re trying, we’re starting a program at Turner Fairbank to address this issue and we’re trying to look at to answer the questions that some of the DOT’s have raised which are basically; Can I use phosphoric acid? Which grades can I use? Which grades can I not use? One of the issues is of course, is it permanent? Do you know if the phosphoric acid is extracted over time? Is that compensated for by hardening of the asphalt? MR. BAUMGARDNER – I think there can be a partial reversal of the reaction with certain amines, but not with all amines. There are some amines that don’t show the same reversal and there also can be some reactions with basic compounds. I think it’s also asphalt dependant. That’s why I say you have to each formulation with each asphalt, and that should be up to the supplier. My personal

Polyphosphoric Acid

recommendation is not to modify more than it takes to make one grade. What you are doing in combination with polymers or with the neat asphalt, use that as a rule of thumb and I think you are, will be more safe. MR. MARTIN – Just one more comment regarding your questions about the lexiviation or the leaching of asphalt in with the poly phosphoric acid linked, what the links are. We’ve done some work and released this work last year at EUROBITUME Topics and where we’ve made the exercise to wash a precipitate asphaltene presently modified with poly phosphoric acid and we haven’t seen any removal of the poly phosphoric acid. Moreover we’ve done some phosphorous NMR a solid phosphorus NMR on it and we found that indeed the poly phosphoric acid was located on the asphaltenes. We didn’t really find the reaction. DR. GERHARD KENNEPOHL – I find your paper quite interesting. I haven’t had the opportunity to read it so I can’t really talk much about the chemistry. But I’m a little bit concerned about the aspect that you outlined and tell me if I misunderstood you. In Saudi Arabian asphalt the modification produced larger quantities of asphaltenes, is that correct? MR. BAUMGARDNER – Actually reduced the asphaltene content – I’m sorry, you’re right increased, both of them increased DR. KENNEPOHL – You also condensed the asphaltenes to make their size 3 or 4 larger than the original ones? MR. BAUMGARDNER – No. DR. KENNEPOHL – You showed the pictures MR. BAUMGARDNER – Right but they actually formed… DR. KENNEPOHL – These had larger cross-linked molecules. MR. BAUMGARDNER – Yes sir, they were larger.


DR. KENNEPOHL – Anyway, given those two observations in your presentations, i.e. increased asphaltenes and larger clusters, it would indicate that the mechanism follows the process of asphalt aging. If you have asphalt for 30 years on the road it stiffens up and this is what’s happening: The asphaltenes increase and form larger clusters. MR. BAUMGARDNER – Well, the comment was that by clustering the asphalt we are simply, basically I think you are saying we are prematurely aging the asphalt right? (Right) We’ve actually done one of the other publications that we have done for the Journal of Rheology, we’re showing that’s not the case. We’re actually making it more resistant to aging by adding, by doing the phosphoric acid modified asphalt. So that’s another paper you need to read. DR. KENNEPOHL – Yes, I have to read the paper. But this is what is observed with the aged asphalts. The asphaltenes increase, resins reduce and the asphaltenes also start building larger clusters. PROF. MARASTEANU – Very nice work. For my own personal information: is this poly phosphoric acid similar to what they put in Pepsi® and Coke®? I know they use phosphoric acid. Is it a different type or the same stuff? MR. BAUMGARDNER – It’s a different type. PROF. MARASTEANU – What is the difference? MR. BAUMGARDNER – Basically I could talk to the acid guys back there, but basically the phosphoric acid in Coke® is phosphoric acid. Poly phosphoric acid is a condensed derivative or ortho phosphoric acid. PROF. MARASTEANU – So it’s safe to drink Pepsi® and Coke®? MR. BAUMGARNDER – Yes. PROF. MARASTEANU – All right. Thank you!

Polyphosphoric Acid

polyphosphoric acid modified asphalt: proposed … professor, physical chemistry, henderson state...

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