Table 7.
Literature review about bitumen modification with polyphosphoric acid (PPA).
| Year | Bitumen type (source) | PPA, wt.% | Other additivesa | Aim of PPA modification | Parameters analyzedb | Principal observations | Reference |
|---|---|---|---|---|---|---|---|
| 1995 | Straight-run bitumen (various undisclosed crude oils) | 1-2 | — | Study the physical and chemical properties of modified bitumen | Pen; SP; FraassT; ageing (RTFO); MW; asphaltenes; 1H, 13C, 31P NMR; morphological and rheological parameters | (i) PPA modification is similar to mild air-blown modification of bitumen, with lower costs (ii) Higher penetration index and ageing resistance with minor losses for low-temperature behavior (iii) Shifting towards a gel structure with higher content and MW of asphaltenes, due to conversion of aromatics to resins and of resins to asphaltenes and to the formation of asphaltene-phosphorous complexes |
[37] |
|
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| 1996 | Straight-run bitumen (various undisclosed crude oils) | 1–5 | Ethylene-propylene copolymers (2–10 wt.%) | Improve storage stability of polymer-modified bitumen | Pen; SP; viscosity; rheological curves; asphaltenes; MW; storage stability; morphology | (i) PPA improves the dispersion of the copolymer in the bitumen, shifting it towards a gel structure with increased content and MW of the asphaltenes fraction (ii) PPA modification imparts higher penetration index, viscosity, and better storage stability at high temperatures (iii) The addition of PPA can reduce copolymer load (by ca. 50%) thus lowering the costs |
[16] |
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| 1999 | Straight-run and visbreaker bitumen (undisclosed source) | 1–3 | Ethylene-propylene copolymers (2 or 5 wt.%) | Study the colloidal structure of polymer-modified bitumen | Pen; SP; MW; asphaltenes; storage stability; rheological parameters | (i) Similar properties for PPA-modified bitumen and air-blown bitumen, except at low temperature (ii) Improved behavior at high temperature, unchanged behavior at low temperature (Fraass brittle point) (iii) Shifting from sol to gel colloidal structure (iv) Higher penetration index and storage stability |
[14] |
|
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| 2000 | Vacuum residue (Middle East) | 1 | — | Improve the rheological and physicochemical properties of vacuum residues | Pen; SP; SARA; 13C NMR; elemental analysis; rheological and colloidal parameters | (i) Higher stiffness, improved elasticity and colloidal stability, and lower thermal susceptibility (ii) Shifting towards a gel type structure (related to more aromatic and polycondensed asphaltenes) (iii) Conversion of maltenes to asphaltenes (iv) Formation of asphaltene-phosphorous complexes |
[13] |
|
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| 2004 | Bitumen blends (Saudi Arabia, Venezuela, and California) | 0.2–0.6 | SBS or EVA polymers (15 wt.%) | Study asphalt mixtures prepared from PPA/polymer-modified bitumen | Pen; SP; SARA; rheological parameters; ageing (RTFO, PAV); moisture resistance | (i) PPA enables the reduction of polymer content without loss of performance properties (ii) Improved processing conditions, high temperature viscosity, and storage stability |
[43] |
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| 2005 | Bitumen (Saudi Arabia, Venezuela) | 0.6–1.2 | — | Study the mechanisms for PPA modification | SARA; MW; 31P NMR; morphology (AFM) | (i) PPA stiffens the matrix (maltenes) or the dispersed phase (asphaltenes) depending on bitumen composition (i.e., source) (ii) Conversion of saturates into asphaltenes (Saudi Arabia) or resins into saturates and asphaltenes (Venezuela) (iii) Formation of asphaltene-phosphorous complexes |
[44] |
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| 2006 | Bitumen (Venezuela, Middle East) | 0.4–1 | — | Study the low-temperature performance (−25°C to +5°C) | Pen; SP; FraassT; rheological and thermal parameters | (i) PPA showed some positive effects on the low-temperature rheological behavior, and this influence depends mainly on the bitumen composition (i.e., source) (ii) PPA lowers the stiffness (at −25°C) and has marginal effects on ductility (at +5°C) |
[22] |
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| 2007 | Bitumen (Venezuela, Middle East) | 0.4–1 | — | Study high/medium temperature performance (+5°C to +100°C) | Pen; SP; ageing (RTFO, PAV); rheological and thermal parameters; FTIR | (i) PPA has a positive effect on the rheological behavior, providing the highest stiffening effects in the range 25 to 90°C (ii) The effect of PPA on the rheological properties depends mainly on the bitumen composition (i.e., source) |
[45] |
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| 2008 | Bitumen model compounds (isoquinoline; 1-methyl-2-quinolone) | 16.7 | — | Study the reaction with pyridine and pyridinone groups | FTIR | (i) Pyridine and pyridinone functional groups form ion pairs with PPA through hydration or by resonance, depending on the dielectric constant (ii) The dissociation and reaction of PPA with bitumen will occur preferentially in enclaves of high dielectric constant |
[7] |
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| 2008 | Bitumen model compounds (sulfur; tetrahydrothiophene; benzothiophene; tetramethylene sulfoxide) | 16.7 | — | Study the reaction with sulfide and sulfoxide groups | FTIR; TLC | (i) Aliphatic and aromatic sulfide groups were inert, at 150°C, thus invalidating the hypothesis of PPA induced nucleophilic displacement reactions (ii) Sulfoxide groups were very reactive with PPA suggesting that oxidized and nonoxidized bitumen will react differently |
[15] |
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| 2008 | Bitumen model compounds (indole) | 3.2 and 16.7 | — | Study the reaction with pyrrole functional groups | FTIR | (i) The amine and double bond of indole are both reactive (ii) The amine group undergoes phosphorylation (iii) N–N bridging increases MW and stiffness (iv) Disruption of the hydrogen bond network (involving pyrrole N–H groups) affects the asphaltenes-maltenes equilibrium (v) Competing bridging and ring opening reactions explain the increase/decrease of stiffness in PPA-modified bitumen |
[46] |
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| 2008 | Bitumen model compounds (bisphenol A; butyl phenyl ether; acetophenone; benzoic acid) | 16.7 | — | Study the reaction with oxygenated functional groups | FTIR; TLC | (i) The reactivity of the functional groups follows the order phenols > ketones > carboxylic acids > ethers (ii) Bisphenol A was fragmented (i.e., lower MW) whereas the other compounds were condensed into higher MW structures (iii) Phosphorylation of hydroxyl groups did not occur, showing that phosphate esters cannot exist in PPA-modified bitumen |
[47] |
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| 2008 | Bitumen ABD (SHRP library)c | 1.5 | SBS or Elvaloy® polymers (3 wt.%) | Study the reactions between PPA and bitumen or polymer-modified bitumen | 31P NMR; storage stability | (i) PPA hydrolyzes back to orthophosphoric acid by reacting with residual water eventually present in bitumen (ii) The formation of organophosphate esters was not detected (iii) There is no evidence of reaction between SBS or Elvaloy polymers and bitumen in the presence of PPA (0.2 wt.%) |
[32] |
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| 2008 | AAD-1, AAM-1, and ABD bitumen (SHRP library)c | 1.5 | — | Study the variation of the rheological and chemical properties of PPA-modified asphalts with ageing time | Rheological and thermal parameters; FTIR; 31P NMR; ageing (PAV); storage stability | (i) PPA addition improves bitumen rheological properties (i.e., higher stiffness and greater elastic modulus) without significant changes in bitumen composition (ii) The effect of PPA depends on the chemical composition of the base bitumen (i.e., its source) (iii) Formation of organic phosphate esters was not observed |
[20] |
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| 2009 | AAA, AAU, AAX, and ABD bitumen (SHRP library)c | 0-1 | — | Study the reaction between PPA and bitumen with known contents of organic functional groups | SARA; MW; morphology (AFM); thermal parameters | (i) PPA acts at the interface between asphaltenes and maltenes, with resins (polar aromatics) playing a crucial role in the disruption of the hydrogen bond network (ii) PPA acts on functional groups with high dielectric constants (i.e., compounds with nitrogen, oxygen, or sulfur) (iii) The hydroxyl groups are not phosphorylated (iv) Tg of maltenes decreases and Tg of asphaltenes increases (v) High temperature performance grade (PG) correlates linearly with PPA content, depending on bitumen composition |
[48] |
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| 2010 | Bitumen (Repsol, Spain) | 2 | Crumb tire rubber (10 wt.%) | Study the properties of crumb rubber modified bitumen | Pen; SP; rheological and thermal parameters; storage stability; insoluble solids | (i) Small quantities of PPA improve the elastic properties of bitumen, due to sol-gel transition; Tg was unaffected (ii) The stage at which PPA is added (before or after mixing with crumb rubber) apparently has no influence (iii) PPA improves storage stability but is not sufficient to avoid sedimentation of crumb rubber particles at high temperature |
[41] |
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| 2010 | Paving bitumen (Lanzhou, China) | 1–3 | SBR, sulfur (0–6 wt.%) | Study the properties of bitumen modified with SBR, sulfur, and PPA | Pen; SP; FTIR; ageing (RTFO); mechanical, thermal, and rheological parameters; morphology; storage stability | (i) PPA shifts the structure from sol to gel improving the high-temperature physical and rheological properties of bitumen (ii) The addition of SBR can reduce the unfavorable effect of PPA on the low-temperature ductility (iii) The addition of sulfur to PPA/SBR-modified bitumen improves the high-temperature rheological properties, with a small effect on thermal stability |
[49] |
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| 2011 | AAD, AAM, and ABD bitumen (SHRP library)c | 1.5 | Hydrated lime (10 wt.%); dolomitic and granite fillers (10–30 wt.%) | Study the effect of hydrated lime and other fillers on the rheological and chemical properties of PPA-modified bitumen | Ageing (RTFO, PAV); 31P NMR; rheological parameters | (i) PPA increases bitumen stiffness (ii) The addition of granite fillers to PPA-modified bitumen has little effect on stiffness whereas dolomite reduces stiffness (iii) The addition of hydrated lime cancels the stiffening effect of PPA but slows down the oxidative ageing process of bitumen (iv) Hydrated lime reacts with PPA yielding calcium phosphates (v) The interaction between hydrated lime, PPA, and the binders is different for sol-type and gel-type bitumen |
[50] |
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| 2011 | PG58-22 bitumen (Iran) | 1-2 | Crumb rubber (5–15 wt.%); Vestnamer® (4.5 wt.% of crumb rubber) | Study the effect of PPA + Vestnamer (synthetic rubber) on crumb rubber modified bitumen | Pen; SP; ageing (RTFO, PAV); morphology; rheological parameters | (i) SP increases and Pen decreases linearly with PPA content (ii) The preferred content of PPA is 1 wt.%, since bitumen performance is improved both at high and at low temperatures (iii) Vestnamer reacts chemically with crumb rubber and bitumen to create a uniform macropolymer network (iv) The addition of PPA promotes the uniform distribution of crumb rubber and synthetic rubber particles in the bitumen, thus improving its rheological properties |
[17] |
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| 2012 | Bitumen (Russia, Saudi Arabia, and Venezuela) | 0.5–1.5 | — | Study the effect of PPA on bitumen behavior at low temperature (<5°C) | Pen; SP; FraassT; asphaltenes; wax content; rheological and thermal parameters | (i) PPA improves the low-temperature performance of bitumen (i.e., stiffness increases and Tg is lowered) up to 1 wt.% (ii) The effect of PPA at low temperature is strongly dependent on bitumen composition (i.e., wax and asphaltene content) |
[21] |
|
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| 2012 | Straight-run bitumen (Venezuela) | 1-2 | — | Study the molecular structure and mechanical behavior of PPA-modified bitumen | 1H-NMR spin-spin relaxation times; rheological parameters | (i) 1% of PPA shifts the sol-gel transition temperature to higher values without bitumen loss of stability, whereas 2% of PPA imparts undesired heterogeneous structures (ii) The distribution of proton relaxation times provides useful information about the macrostructure of bitumen |
[51] |
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| 2013 | Bitumen (Saudi Arabia, China) | 0.5–2 | — | Study the effect of PPA on chemical composition, physical properties, and morphology of bitumen | Pen; SP; ductility; viscosity; SARA fractions; morphology (AFM) | (i) PPA apparently converts the resins into asphaltenes (ii) The effect of PPA depends on the type of bitumen, having a lower influence on bitumen with higher contents of resins and lower asphaltenes content (iii) In general, viscosity and SP increase with PPA content whereas Pen and ductility decrease (iv) Morphology and chemical composition of PPA-modified bitumen correlates strongly with the colloidal index |
[32] |
|
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| 2013 | Bitumen (Russia, Saudi Arabia, and Venezuela) | 0.5–1.5 | — | Study the changes induced by PPA in bitumen to relate its rheological properties and morphology | Pen; SP; morphology (SEM); rheological parameters | (i) PPA improves the high-temperature properties (i.e., extends the range of viscoelastic behavior), mainly due to the size reduction of asphaltenes micellar aggregates which improves solvation phenomena and colloidal stability (ii) The transition temperature from sol to gel increases with PPA concentration up to 1 wt.% and not so much for higher concentrations (depending on asphaltene content) suggesting the existence of saturation effects |
[2] |
|
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| 2014 | Bitumen (USA) | 0.5 | SBS; PPMA oxidized PE (2-3 wt.%); crumb rubber (10 wt.%) | Study the high temperature rheological properties of polymer-modified bitumen | Rheological parameters; ageing (RTFO, PAV) | (i) The addition of PPA (0.5 wt.%) can reduce polymer loading (from 3% to 2%) required to obtain the same bitumen grade (ii) The rheology of modified bitumen is source-dependent (iii) Oxidized PE and PPMA provided bitumen with lower viscosity values compared to SBS and crumb rubber, thus needing lower energy for mixing/compaction of the mixtures |
[52] |
|
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| 2014 | Bitumen (Petrobras, Brazil) | 0.5–1.2 | LDPE (3–6 wt.%) | Study high/medium temperature performance of LDPE-modified bitumen | Rheological parameters; ageing (RTFO, PAV) | (i) PPA improves the rheological properties (rutting and fatigue resistance) of the base bitumen, retaining performance grade (ii) Addition of PPA alone provides better improvements than modification with LDPE (with and without PPA) |
[53] |
aEVA: ethylene vinyl acetate, HDPE: high density polyethylene, LDPE: low density polyethylene, PE: polyethylene, PPMA: polypropylene-maleic anhydride, SBR: styrene-butadiene rubber, and SBS: styrene-butadiene-styrene block copolymers.
bAFM: atomic force microscopy, FraassT: Fraass breaking point temperature, FTIR: Fourier transform infrared spectroscopy, GPC: gel-permeation chromatography, MW: molecular weight, NMR: nuclear magnetic resonance spectroscopy, PAV: pressure ageing vessel test (long-term ageing ASTM D6521), Pen: penetration depth; RTFO: rolling thin film oven test (short-term ageing ASTM D2872), SARA: analysis of saturates, aromatics, resins, and asphaltenes, SEM: scanning electron microscopy, SP: softening temperature (ring and ball method), Tg: glass transition temperature, and TLC: thin-layer chromatography.
cSHRP: Strategic Highway Research Program.