Phosphoric Acid Phosphoric Acid Modification of Asphalt Modification of Asphalt

BindersBinders

Terry ArnoldTerry ArnoldPavement Materials & Construction Team, R&DPavement Materials & Construction Team, R&D

Federal Highway AdministrationFederal Highway Administrationwww.TFHRC.govwww.TFHRC.gov

OutlineOutline

•• Problem statementProblem statement•• Literature reviewLiterature review•• Proposed work planProposed work plan•• Solicit commentsSolicit comments

Problem StatementProblem Statement

•• Acid modification has been shown to be a low cost way Acid modification has been shown to be a low cost way to increase the high temperature stiffness of asphalt to increase the high temperature stiffness of asphalt binders (per Superpave Binder Specification) but…binders (per Superpave Binder Specification) but…

•• Studies have shown both beneficial and harmful effects Studies have shown both beneficial and harmful effects of acid modification.of acid modification.

•• HHow should it be used?ow should it be used?•• HHow should it not be used?ow should it not be used?•• WWhat are the pitfalls to avoid?hat are the pitfalls to avoid?

AcknowledgementsAcknowledgements• Western Association of State Highway and Transportation

Officials (WASHTO)• “Impact of different types of modification on low-temperature

tensile strength and Tcritical of asphalt binders.” Ho, Zanzotto & MacLeod (TRB 1810)

• “Modification with Acid – Advantages and Disadvantages”Bishara, Mahoney Reynolds & King, Kansas DOT Report FHWA-KS-02-2,

• Nebraska DOT Laird Weishahn, private communication• Western Cooperative Test Group (WCTG)• Baumgardner Private Communication• “Polyphosphoric Acid Modified Asphalt” Baumgardner, Masson,

Hardee et al. AAPT 2005 Under Review• “Acid/Base Chemistry for Asphalt Modification” King Bishara &

Fager AAPT 2002• King Private Communication

Findings Findings Regarding PPA ModificationRegarding PPA Modification

•• 2% PPA (85%) increases the high temperature stiffness 2% PPA (85%) increases the high temperature stiffness in the range of 11.4 to 18°C or 2 to 3 PG Gradesin the range of 11.4 to 18°C or 2 to 3 PG Grades

•• The amount of the increase is binder specificThe amount of the increase is binder specific

•• Low temperature stiffness or mLow temperature stiffness or m--value is essentially value is essentially unchangedunchanged

•• PPA in optimal amounts PPA in optimal amounts (0.3(0.3--0.7%) did not contribute0.7%) did not contributeto moisture sensitivity or to moisture sensitivity or ruttingrutting

Purported Negative Effects of Purported Negative Effects of Acid ModificationAcid Modification

•• High temperature improvements were reversed by the High temperature improvements were reversed by the reaction between the acid and hydrated lime or amine reaction between the acid and hydrated lime or amine antistripantistrip

•• Nullifies the effect of amine antiNullifies the effect of amine anti--stripsstrips•• Cracking of ICracking of I--80 in Nebraska, 186 cracks/mile with 80 in Nebraska, 186 cracks/mile with

acid, 6 withoutacid, 6 without•• Responsible for road failures in KS, OK and MO?Responsible for road failures in KS, OK and MO?

WASHTO Acid Modification WASHTO Acid Modification Study ProposalStudy Proposal

•• Which works best? Polyphosphoric, orthophosphoric or Which works best? Polyphosphoric, orthophosphoric or green acid?green acid?

•• Can it reduce the effectiveness of lime?Can it reduce the effectiveness of lime?•• Is the effect transitory in mixes Is the effect transitory in mixes –– does rut resistance does rut resistance

disappear?disappear?•• Is polymer + acid better than polymer alone?Is polymer + acid better than polymer alone?•• Are there longAre there long--term mix and pavement performance term mix and pavement performance

issues?issues?•• How can an agency identify and monitor the optimum How can an agency identify and monitor the optimum

level?level?•• Binder extraction methods need to be developed in order Binder extraction methods need to be developed in order

to recovered binders that reflect their into recovered binders that reflect their in--place properties.place properties.

What is the Chemistry?What is the Chemistry?

•• PPA modification gives rise to higher levels of PPA modification gives rise to higher levels of asphaltenes. Venezuelan Asphalt showed an increase asphaltenes. Venezuelan Asphalt showed an increase from 10.5% to 14.9%from 10.5% to 14.9%

•• PP3131 NMR showed no phosphorous in the asphaltenes NMR showed no phosphorous in the asphaltenes from unmodified binders, but did show it present in PPA from unmodified binders, but did show it present in PPA modified bindersmodified binders

•• Can we use this to identify what is happening?Can we use this to identify what is happening?

Work Done So Far Work Done So Far --Baumgardner et al:Baumgardner et al:

•• AFM Atomic Force MicroscopyAFM Atomic Force Microscopy•• PP3131 NMR NMR •• TLC Thin Layer Chromatography TLC Thin Layer Chromatography –– molecular sizemolecular size•• GPC Gel Permeation Chromatography GPC Gel Permeation Chromatography –– molecular molecular

weightweight•• Water extraction of toluene / binder solutionsWater extraction of toluene / binder solutions•• SPME on water fractionsSPME on water fractions•• Iatroscan Iatroscan hydrocarbon analyses on binders hydrocarbon analyses on binders •• Asphaltene determinationsAsphaltene determinations

Work Done So Far Work Done So Far ––King, King, Bishara Bishara and and FagerFager

•• Binder DSR study with acid & Binder DSR study with acid & imidazolene imidazolene antistripsantistrips

•• Investigated pH and emulsification potentialInvestigated pH and emulsification potential•• Mix study of moisture resistance using HWTD and Mix study of moisture resistance using HWTD and

APAAPA•• Findings: Findings:

–– Moisture damage may occur if acid is present in high Moisture damage may occur if acid is present in high concentrationsconcentrations

–– ASAs ASAs significantly reduced moisture damagesignificantly reduced moisture damage–– Wheel tracking tests predict significant moisture damageWheel tracking tests predict significant moisture damage–– TThh substantially reduced if acid and amine ASA used in substantially reduced if acid and amine ASA used in

the same mixthe same mix

Suggested Methodologies and CommentsSuggested Methodologies and Comments

•• Need specifications to control the use/misuse of acidsNeed specifications to control the use/misuse of acids

•• Need a good study of field projects using acids.Need a good study of field projects using acids.

•• Environmental factors need to be further examined:Environmental factors need to be further examined:–– Need Moisture Damage tests that create pore pressure Need Moisture Damage tests that create pore pressure ––

Hamburg or Pine Rut Tester probably best betsHamburg or Pine Rut Tester probably best bets–– Are PPA modified binders less susceptible to aging and Are PPA modified binders less susceptible to aging and

subsequent subsequent embrittlementembrittlement? ? –– What is the effect of actinic light?What is the effect of actinic light?

Phosphoric AcidsPhosphoric AcidsA Brief ReviewA Brief Review

•• Made in vast quantitiesMade in vast quantities•• Direct reaction of phosphate rock (calcium phosphate or Direct reaction of phosphate rock (calcium phosphate or

apatite with sulfuric acidapatite with sulfuric acid•• This yields “Green Acid” typically 25This yields “Green Acid” typically 25--30% H30% H33POPO4 4 heavily heavily

contaminated with impurities like chloride and sulfate contaminated with impurities like chloride and sulfate ––corrosion issues?corrosion issues?

•• Also made by burning phosphorous to PAlso made by burning phosphorous to P44OO1010 and and subsequent hydrationsubsequent hydration

•• Acid has tetrahedral POAcid has tetrahedral PO44 groups connected by hydrogen groups connected by hydrogen bonds which makes the acid syrupybonds which makes the acid syrupy

Phosphoric Acid Grades AvailablePhosphoric Acid Grades Available

•• Orthophosphoric Acid (HOrthophosphoric Acid (H33POPO44) as 50%, 75%, 85%, 100%) as 50%, 75%, 85%, 100%•• Polyphosphoric acids have the general formula Polyphosphoric acids have the general formula

HHnn+2+2PPnnOO3n+13n+1 for n>1for n>1•• Polyphosphoric acids range from pyrophosphoric acid Polyphosphoric acids range from pyrophosphoric acid

HH44PP22OO77 (n=2) to metaphosphoric acid (large values of n)(n=2) to metaphosphoric acid (large values of n)•• Polyphosphoric Acid sold commercially is a mixture of Polyphosphoric Acid sold commercially is a mixture of

orthophosphoric acid with pyrophosphoric acid, orthophosphoric acid with pyrophosphoric acid, triphosphoric acid and higher acids and is sold on the triphosphoric acid and higher acids and is sold on the basis of its calculated content of Hbasis of its calculated content of H33POPO44,, 115%, e.x.115%, e.x.

•• SuperphosphoricSuperphosphoric Acid is a similar mixture sold at 105% Acid is a similar mixture sold at 105% HH33POPO44

Proposed Work PlanProposed Work Plan•• Forensic method for determining type and Forensic method for determining type and

level of phosphate additivelevel of phosphate additive•• Durability of acid modificationDurability of acid modification

–– Effect of environment: actinic light, water, etc.Effect of environment: actinic light, water, etc.

•• Address corrosion and handling issuesAddress corrosion and handling issues•• Optimization of acid modificationOptimization of acid modification

–– Chemical / mechanistic considerationsChemical / mechanistic considerations–– Different AsphaltsDifferent Asphalts–– Physical PropertiesPhysical Properties

ThanThank you.k you.

Questions?Questions?