Relationship between the age related performance of a typical bituminous binder in South Africa and the fatigue performance of the asphalt mixture

Van Zyl, Stiaan (2018-03)

Thesis (MEng)--Stellenbosch University, 2018.

Thesis

ENGLISH ABSTRACT: The primary factor affecting the durability of bituminous binders is ageing. Ageing causes an increase in stiffness which leads to non-load associated cracking in asphalt mixtures. Laboratory ageing has been used to determine the change in a binder’s rheology to predict how a binder would age in the field. Age-related parameters are calculated from a binder’s properties to determine a binder’s behaviour when exposed to ageing. These parameters give an indication of the rate of ageing. An asphalt mixture in a pavement structure is subjected to repeated loading rendering the asphalt mixture to deteriorate. This phenomenon is called fatigue. Fatigue, in asphalt, has become one of the major distress modes in a flexible pavement structure. The fatigue life of a pavement is predominantly influenced by the stiffness of the asphalt mixture, which in turn is influenced by the stiffness of the binder. Binders were subjected to different levels of ageing to determine the age-related parameters that indicate the degree of ageing of a binder. The binders were subjected to 4 different levels of ageing resulting in five different ages, namely Unaged, RTFO, PAV1, PAV2 and PAV4. The Dynamic Shear Rheometer (DSR) and Bending Beam Rheometer (BBR) were used to determine the rheological properties of the binders. Models were used to predict the behaviour of the binders and to calculate the age-related parameters. Asphalt beams were produced to simulate repeated loading on an asphalt mixture. The stiffness of the asphalt mixture was determined by performing tests at different temperatures. Thereafter, the fatigue life of the asphalt mixture was determined at two different temperatures. The age-related performance of the binder was analysed with the fatigue performance of the asphalt mixture to determine a relationship between the age-related performance of a binder and the fatigue performance of the asphalt mixture. The Glover-Rowe (G-R) parameter gives an indication to the ductility of a material at intermediate temperatures and is used to assess the ageing of a binder. The DTc parameter, on the other hand, indicates the thermal cracking at lower temperatures and is used to assess the thermal cracking susceptibility after ageing. The G-R parameter gave a good correlation with the DTc parameter. Both described the ageing of the binder due to laboratory ageing very well. The G-R parameter was used as the age-related parameter of the binder to obtained a relationship. The fatigue results performed on the asphalt mixture at two temperatures showed a good correlation with each other regarding the slope of the fatigue-strain relationship. A relationship between the age-related parameter of the binder and the fatigue of the asphalt mixture was obtained.

AFRIKAANSE OPSOMMING: Die primêre faktor wat die duursaamheid van bitumineuse bindmiddels beïnvloed is veroudering. Veroudering veroorsaak ’n toename in styfheid wat lei tot nie-vragverwante krake in ’n asfaltmengsel. Laboratoriumeroudering is gebruik om die verandering in ’n bindmiddel se reologie te bepaal en om te voorspel hoe ’n bindmiddel in die veld sal verouder. Ouderdomsverwante parameters word bereken vanuit die reologiese eienskappe van ’n bindmiddel om sy gedrag te bepaal wanneer dit aan veroudering blootgestel word. Hierdie parameters gee ’n aanduiding van die verouderingstempo. ’n Asfaltmengsel in ’n padstruktuur word aan herhaalde lading blootgestel, wat die asfaltmengsel laat verswak. Hierdie verskynsel word vermoeiing genoem. Vermoeiing is een van die grootste falingsmeganismes wat in buigsame padstrukture voorkom. Die vermoeiingslewe van ’n padstruktuur word hoofsaaklik beïnvloed deur die styfheid van die asfaltmengsel, wat op sy beurt beïnvloed word deur die styfheid van die bindmiddel. Bindmiddels is onderwerp aan verskillende vlakke van veroudering om die ouderdomsverwante parameters te bepaal wat die mate van veroudering van ’n bindmiddel aandui. Die bindmiddels is onderwerp aan 4 verskillende vlakke van veroudering wat lei tot vyf verskillende ouderdomme naamlik Unaged, RTFO, PAV1, PAV2 en PAV4. Die Dynamic Shear Rheometer (DSR) en Bending Beam Rheometer (BBR) is gebruik om die rheologiese eienskappe van die bindmiddels te bepaal. Modelle is gebruik om die gedrag van die bindmiddels te voorspel en die ouderdomverwante parameters te bereken. Asfaltbalke is vervaardig om herhaalde lading op ’n asfaltmengsel te simuleer. Die styfheid van die asfaltmengsel is bepaal deur toetse by verskillende temperature uit te voer. Die vermoeiingslewe van die asfaltmengsel is daarna by twee verskillende temperature bepaal. Die ouderdomverwante gehalte van die bindmiddels is geanaliseer saam met die vermoeiing van die asfaltmengsel om ’n verhouding tussen die ouderdomverwante gehalte van ’n bindmiddel en die vermoeiing van die asfaltmengsel te bepaal. Die Glover-Rowe-parameter (G-R) gee ’n aanduiding van die duktiliteit van ’n materiaal by intermediê re temperature en word gebruik om die veroudering van ’n bindmiddel te bepaal. Die DTc parameter dui aan die termiese kraak teen laer temperature en word gebruik om die termiese kraakvatbaarheid na veroudering te bepaal. Die G-R parameter het ’n goeie korrelasie met die DTc parameter getoon. Albei beskryf die veroudering van die bindmiddel as gevolg van laboratorium veroudering baie goed. Die G-R parameter is gebruik as die ouderdomsverwante parameter van die bindmiddel om ’n verwantskap te verkry. Die vermoeiing resultate op die asfaltmengsel by twee temperature het ’n goeie korrelasie met mekaar gehad ten opsigte van die helling van die vermoeing-spanning verhouding. ’n Verwantskap tussen die ouderdomverwante parameter van die bindmiddel en die vermoeiing van die asfaltmengsel is verkry.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/103414
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