Rheological performance of seals in South Africa based on binder ageing considerations

Tredoux, Carlie (2020-03)

Thesis (MEng)--Stellenbosch University, 2020.

Thesis

ENGLISH ABSTRACT: Ageing is a fundamental phenomenon that affects the durability and performance of bituminous binders in a pavement. Ageing increases the risk of premature pavement failures whilst reducing the material durability and flexibility thus shortening pavement life. For this reason the South African pavement industry is currently moving away from Penetration and Viscosity Grade (empirical) Specifications and towards Performance Grade (fundamental) Specifications, as the current specifications do not account for ageing in a comprehensive, fundamental manner. To facilitate the transitional process, a proposed technical specification for SA Performance Grade (PG) Specification for Bitumen (SATS 3208) was published by the South African Bureau of Standards (SABS) in 2018. Currently, this Performance Grade Specification is based on asphalt as per SHRP Superpave, hence the need for consideration of seal binders. In order to make a meaningful contribution towards the formulation of a comprehensive PG specification for SA bituminous binders with respect to seals this study’s aim is to investigate the performance of seals in South Africa. In particular, changes in the fundamental rheological properties of seal binders during ageing are of interest. These measurements provide performance-based properties that are essential as binder selection criteria. This study was undertaken by performing laboratory testing on seal binders. It includes Dynamic Shear Rheometer (DSR) testing in accordance with SATS 3208 at intermediate temperatures and on seven different levels of ageing (unaged, RTFO, PAV2, RTFO+PAV2, PAV4, RTFO+PAV4 and recovered age). The seal binder’s behavioural data was analysed with the Modified Kaelble shift factor model, CAM and GLS empirical models to determine / investigate rheological parameters that describes the durability and performance of seals in relation to ageing. Results from the investigation show the Glover-Rowe (G-R) parameter to be the best rheological parameter to identify seal performance with age, as the Rheological Index (R) showed no correlation to seal ageing. Further investigation is required on SA seals, regarding the VET parameters influence on aggregate loss (failure mechanisms) before performance limits can be proposed for performance specifications. Ageing influences the rheological properties of modified seal binders, as long-term artificial ageing of polymer modified seal binder provides an increased viscous component, thus showing that the polymer degrades at high temperatures as the binder ages. Visual assessment on seal roads is recommended after 6-8 years of in-service to determine deterioration (failure mechanisms) of the pavement, based the G-R data findings of this study and others.

AFRIKAANSE OPSOMMING: Veroudering is 'n fundamentele verskynsel wat die duursaamheid en werkverrigting van bitumen-bindmiddel in 'n plaveisel beïnvloed. Veroudering verhoog die risiko van voortydige falings tydens die plaveisel, terwyl die materiaal duursaamheid en buigsaamheid verminder word, waardeur plaveisel se lewe verkort word. Om hierdie rede beweeg die Suid-Afrikaanse plaveiselbedryf tans weg van die Penetrasie en Viskositeit Graad (empiriese) spesifikasies en na die Werksverrigtingspesifikasies (fundamentele), aangesien die huidige spesifikasies nie op 'n omvattende, fundamentele manier veroudering in ag neem nie. Om die oorgangsproses te vergemaklik, is 'n voorgestelde tegniese spesifikasie vir SA Werksverrigtingspesifikasies vir Bitumen (SATS 3208) in 2018 deur die Suid Afrikaans Bureau van Standaarde (SABS) gepubliseer. Tans is hierdie Werksverrigtingspesifikasies gebaseer op asfalt volgens SHRP Superpave, daarom moet seëlbinders oorweeg word. Om 'n betekenisvolle bydrae te lewer tot die formulering van 'n omvattende Werksverrigtingspesifikasie vir SA bitumen-bindmiddels ten opsigte van seëls, is hierdie studie se doel om die werkverrigting van seëls in Suid-Afrika te ondersoek. Veral die veranderinge in die fundamentele reologiese eienskappe van seëlbinders tydens veroudering is van belang. Hierdie metings bied werkverrigting-gebaseerde eienskappe wat noodsaaklik is vir bindingseleksie-kriteria. Hierdie studie is onderneem deur laboratoriumtoetse op seëlbinders uit te voer. Dit sluit Dynamic Shear Rheometer (DSR) -toetse in volgens die SATS 3208 by intermediêre temperature en op sewe verskillende verouderingsvlakke (onverouderd, RTFO, PAV2, RTFO + PAV2, PAV4, RTFO + PAV4 en herwonne ouderdom). Die gedragsgegewens van die seëlbinder is met die Aangepaste Kaelble verskuiffaktor model, CAM en GLS empiriese modelle geanaliseer om reologiese parameters te bepaal / ondersoek wat die duursaamheid en werkverrigting van seëls in verhouding tot veroudering beskryf. Ondersoekresultate het getoon dat die Glover-Rowe (G-R) parameter die beste reologiese parameter was om seëlprestasie met ouderdom te identifiseer, aangesien die Reologiese Indeks (R) geen korrelasie met seëlveroudering getoon het nie. Verdere ondersoek is nodig op SA seëls met betrekking tot die visko-elastiese oorgangsparameters invloed op klipverlies (falingmeganismes) voordat werkverrigting limiete vir Werksverrigtingspesifikasies voorgestel kan word. Veroudering beïnvloed die reologiese eienskappe van gemodifiseerde seëlbinders, aangesien langtermyn kunsmatige veroudering van polimeermodifiseerde seëlbindmiddels ʼn verhoogde viskose komponent lewer, dit toon aan dat die polimeer by hoë temperature afbreek soos die bindmiddel verouder. Na 6-8 jaar van diens word visuele assessering op seëlpaaie aanbeveel om die agteruitgang (falingmeganismes) van die plaveisel te bepaal, wat gebaseer is op die bevindings van die G-R data van hierdie studie en andere.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/107793
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