Polymer modified asphalt binders (PMB) are being commonly adopted instead of neat binders when superior performance is needed during the road service life. The polymer addition indeed increases binder’s properties at high, low and mid-range temperatures. However, PMBs improved skills need a chemical-structural modification in binder’s composition in order to be effective and durable. The phase inversion phenomenon between binder’s ordinary components and added polymer leads the binder to assimilate the polymer characteristics. Supplied binders, all available on the market with the same declared performance, were tested in several ways. Physical tests, as Softening Point (EN 1427), Penetration (EN 1426), Elastic Recovery (EN 13398) and Brookfield Viscosity (EN 13302), demonstrated how these PMBs behave differently related with the type and percentage of the added polymer, neat binder’s properties and phase inversion depth. Due to the presence of the polymer phase, PMBs can be subjected to stability problems and separation; in fact, polymers and bitumen components can separate during the storing phase losing most of the benefits deriving from the modification procedure. Common testing for storage stability assessment includes the cigar tuben test (EN 13399); in addition, the present study analyzed storage stability and separation phenomena of five PMBs by performing an “advanced-rheological storage stability test”, based on frequency sweep tests on samples taken from the top and bottom part of 3, 5 and 7-day stored cigars. Master curves, for unstored and several stored conditions, were compared to identify possible separation phenomena between top and bottom samples. Indices were also developed to quantify separation of samples. Results highlighted how storage stability problems commonly start at the third days of storage; in addition, binders which were seriously affected by separation, seemed to incrementally lose their homogeneity (top and bottom part) after 7 days. On the other hand, other binders preserved their rheological characteristics from being affected by storage, maintaining equal values between top and bottom part over time. Long-term stored binders were all affected by an aging factor. Greater importance was reserved for PMBs rheology. Master curves, through frequency sweep (AASHTO TP135-12), rutting (AASHTO TP70) and fatigue resistance (AASHTO TP101-14), and low temperature behavior (AASHTO TP313-02) tests were developed before and after aging. Rheological experiments showed a great variability in binders results, making them difficult to compare despite their supposed analogy. Aging, as expected and reported in many literature studies, highly affected binders structures leading to a loss of properties and performance. Chemical tests were finally performed for understanding differences in chemical structure coming after polymer addition. Fluorescence microscope helped us in evaluating the effectiveness of the phase inversion while the SARA indices provided important information about asphaltenes and polymer content.
La costante richiesta di aumentare le prestazioni dei bitumi nel mondo delle pavimentazioni ha portato allo sviluppo di bitumi additivati con polimeri. Tale modifica pemette il miglioramento delle caratteristiche del materiale su tutta la scala delle temperature di utilizzo, dalle basse alle alte, in modo di prevenire fenomeni come fatica e ormaiamento, resistere a carichi maggiori e allungare la vita utile della pavimentazione. Il processo di modifica porta all’assorbimento da parte della matrice bituminosa delle caratteristiche della fase polimerica aggiunta; il compimento della modifica si ottiene con “l’inversione di fase”, ossia la fase polimerica domina e prevale sulla fase bituminosa inglobandone e migliorandone le qualità. I bitumi modificati considerati in questo studio, tutti disponibili sul mercato con le medesime caratteristiche o grado di prestazione, sono stati studiati al fine di valutare tutte le loro proprietà. Le prove fisiche condotte, ossia Punto di Rammollimento (EN 1427), Penetrazione (EN 1426), Recupero Elastico (EN 13398) e viscosità Brookfield (EN 13302), mostrano una grande differenza nel comportamento dei materiali; la principale causa di questo divario risiede nella struttura chimica del polimero, nella quantità di polimero e nelle proprietà del bitume di base. Un aspetto chiave dei bitumi modificati è la loro capacità di mantenersi stabili, ossia non separare fase bituminosa e polimerica, durante periodi di stoccaggio statico ad alte temperature. La normativa propone una semplice prova di rammollimento con provini provenienti da porzioni superiore e inferiore di un tubo di alluminio stoccato tre giorni a 180°C (EN 13399); tale test non è però in grado di evidenziare eventuali fenomeni di separazione. A tal fine una prova di stabilità avanzata è stata eseguita per campioni sottoposti a 3-5 e 7 giorni di stoccaggio. Per ogni campione venivano estratti i provini da porzioni superiore e inferiore e su di esse eseguite prove di frequency sweep in modo da costruire e paragonare le curve maestre di bitumi stoccati per diversi periodi e confrontate con curve di bitume non stoccato. Studiando l’andamento delle curve maestre è possibile valutare la presenza di fenomeni di separazione e quantificarla attraverso parametri. Lo studio principale di questo elaborato è stato condotto sul comportamento reologico. Prove di frequency sweep (AASHTO TP135-12), necessarie per creare le curve maestre, prove di ormaiamento (AASHTO TP70), prove di fatica (AASHTO TP101-14) e prove di flessione alle basse temperature (AASHTO TP313-02) sono state eseguite prima e dopo azione invecchiante. Dai risultati ottenuti da tali prove è evidente la grande diversità dei singoli bitumi. L’ossidazione provocata dall’invecchiamento, come dimostrato in numerosi studi di letteratura, provoca una sostanziale diminuizione delle proprietà dei materiali. Studi chimici hanno infine permesso di valutare il grado di completezza dell’inversione di fase dei bitumi acquistati e di capirne la struttura interna, in termine di percentuale di asfalteni e polimero, e la loro relazione con proprietà reologiche e azione invecchiante.
Physical, rheological and chemical characterization of polymer modified binders
ZANI, LORENZO
2014/2015
Abstract
Polymer modified asphalt binders (PMB) are being commonly adopted instead of neat binders when superior performance is needed during the road service life. The polymer addition indeed increases binder’s properties at high, low and mid-range temperatures. However, PMBs improved skills need a chemical-structural modification in binder’s composition in order to be effective and durable. The phase inversion phenomenon between binder’s ordinary components and added polymer leads the binder to assimilate the polymer characteristics. Supplied binders, all available on the market with the same declared performance, were tested in several ways. Physical tests, as Softening Point (EN 1427), Penetration (EN 1426), Elastic Recovery (EN 13398) and Brookfield Viscosity (EN 13302), demonstrated how these PMBs behave differently related with the type and percentage of the added polymer, neat binder’s properties and phase inversion depth. Due to the presence of the polymer phase, PMBs can be subjected to stability problems and separation; in fact, polymers and bitumen components can separate during the storing phase losing most of the benefits deriving from the modification procedure. Common testing for storage stability assessment includes the cigar tuben test (EN 13399); in addition, the present study analyzed storage stability and separation phenomena of five PMBs by performing an “advanced-rheological storage stability test”, based on frequency sweep tests on samples taken from the top and bottom part of 3, 5 and 7-day stored cigars. Master curves, for unstored and several stored conditions, were compared to identify possible separation phenomena between top and bottom samples. Indices were also developed to quantify separation of samples. Results highlighted how storage stability problems commonly start at the third days of storage; in addition, binders which were seriously affected by separation, seemed to incrementally lose their homogeneity (top and bottom part) after 7 days. On the other hand, other binders preserved their rheological characteristics from being affected by storage, maintaining equal values between top and bottom part over time. Long-term stored binders were all affected by an aging factor. Greater importance was reserved for PMBs rheology. Master curves, through frequency sweep (AASHTO TP135-12), rutting (AASHTO TP70) and fatigue resistance (AASHTO TP101-14), and low temperature behavior (AASHTO TP313-02) tests were developed before and after aging. Rheological experiments showed a great variability in binders results, making them difficult to compare despite their supposed analogy. Aging, as expected and reported in many literature studies, highly affected binders structures leading to a loss of properties and performance. Chemical tests were finally performed for understanding differences in chemical structure coming after polymer addition. Fluorescence microscope helped us in evaluating the effectiveness of the phase inversion while the SARA indices provided important information about asphaltenes and polymer content.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/120205