Identifying Gradings and binder combinations for improving the grey water resistance of asphalt

Nel, Christiaan Ludolph Marais (2017-03)

Thesis (MEng)--Stellenbosch University, 2017.

Thesis

ENGLISH ABSTRACT: Premature failure of asphalt surfacing was observed on roads in areas within and surrounding informal settlements in Cape Town. It was concluded that the main source of failure was as a result of grey water spillage onto these road surfaces. Mew Way, located in the Khayelitsha area on the Cape Flats, required treatment and surfacing at least every 5 years to address grey water related problems. This has prompted the City of Cape Town and SABITA to initiate the Grey Water Resistant Asphalt Study to investigate the influence of grey water on the performance of asphalt. As part of the Grey Water Resistant Asphalt Study, extensive laboratory experiments and testing were required to investigate the grey water resistance of asphalt. The University of Stellenbosch was approached by the Grey Water Research Group under the leadership of Mr A. Greyling, Technical Director at BVi Consulting Engineers (Pty) Ltd, to develop a research methodology for this unique study. This research methodology was executed at the University of Stellenbosch where all results and conclusions related to this study were reported. The Researcher, after initiating an extensive literature study and identifying factors for improving the grey water resistance of asphalt, developed primary and secondary research methodologies. The objective of the primary research methodology was to identify gradings and binder combinations to improve the grey water resistance of asphalt. This research methodology consisted of two phases. Phase 1 included moisture inducing simulating tests (MIST) for moisture conditioning purposes and indirect tensile strength (ITS) tests. Tensile strength ratio (TSR) results of binder combinations that were tested during Phase 1, indicated that the retained strength of asphalt mixtures after grey water MIST was significantly lower when compared to clean water MIST conditioning. Results also indicated that a medium graded asphalt mixture achieved greater strength after grey water MIST conditioning when compared to fine graded asphalt mixtures. The binder additive EVA contributed significantly to achieving greater asphalt mixture strength after grey water MIST conditioning. Phase 2 consisted of laboratory scale model mobile load simulating (MMLS) and ITS testing of asphalt briquettes subjected to trafficking under dry (no water) and wet (grey water) conditions. Results from Phase 1 assisted with setting up asphalt gradations and binder combinations for testing during Phase 2 of the primary research methodology. TSR results from Phase 2 did not show significant variations between the performance of medium and fine graded asphalt mixtures after being subjected to wet (grey water) MMLS3 trafficking. However, permanent deformation results indicated that medium graded asphalt mixtures with EVA and SBS modified binders produced significantly lower deformations when compared to virgin binder (50/70 penetration grade) combinations after being subjected to wet MMLS3 trafficking. A binder additive, ZycoTherm®, in combination with an EVA modified binder and Sasobit did not only assist in reducing the permanent deformation, but also significantly increased the strength of the asphalt. ITS, permanent deformation, texture and material loss results of Phase 2 were combined to establish a rating criteria for determining suitable grey water resistant asphalt mixtures for high and low volume roads. Medium graded asphalt mixtures may provide a suitable grey water resistant asphalt mixture for high volume roads, whereas fine graded asphalt mixtures may provide a suitable solution for low volume roads. Based on the results of the rating criteria, the following asphalt mixtures showed significant resistance to grey water: . EVA + 1%Sasobit® + Extra Lime (COLTO Medium Continuous Graded) . EVA + Extra Lime (COLTO Medium Continuous Graded) . EVA + 1%Sasobit® (COLTO Fine Continuous Graded) . EVA + 1%Sasobit® + 0.1%ZycoTherm® (COLTO Fine Continuous Graded) After completing laboratory scale MMLS trafficking during Phase 2 of the primary research methodology, trafficked asphalt briquettes were subjected to ITS testing. Each asphalt briquette had a diameter of 150 mm, and during the preparation of test specimens for laboratory scale MMLS trafficking, two opposite segments with parallel chords and each having a 19 mm mid-ordinate, had to be machined-off from each briquette with a dual saw. This was done to fit nine asphalt briquettes in a test bed specifically designed for executing the laboratory scale MMLS trafficking procedure. This led to the setup of a secondary research methodology for investigating the influence of these removed segments on the indirect tensile strength of the shaped asphalt briquettes. This investigation was accomplished through linear-elastic finite element modelling. Results of the secondary research methodology indicated that a decrease of up to 8% in the maximum tensile strength can be expected at the centre of a shaped asphalt briquette (with removed segments as described above) when compared to an unshaped asphalt briquette. Results also indicate that no significant changes occurred in compressive stresses due to the shaping of briquettes. This study provides insight on the development of grey water susceptible asphalt mixtures, which serves as a starting point for ensuring that durability and user specifications for roads exposed to grey water are met.

AFRIKAANSE OPSOMMING: Die storting van gryswater oor die asfaltlaag van interne paaie binne en aangrensend tot informele nedersettings in Kaapstad, was geïdentifiseer as sleutelprobleem tot versnelde faling van die padstruktuur. Mew-weg, ‘n pad aan die buitewyke van Khayelitsha op die Kaapse Vlakte, is een van hierdie paaie waar gryswater-verwante probleme tot behandeling en herbedekking ten minste elke 5 jaar gelei het. Die Stad Kaapstad en SABITA het saamgespan om die Gryswater Weerstandige Asfalt Studie te loods om invloed van gryswater op die gedrag van asfalt te ondersoek. Deel van die Gryswater Weerstandige Asfalt Studie behels die uitvoer van toepaslike en uitgebreide laboratorium eksperimente rondom die gryswater-weerstandigheid van asfalt. Die Universiteit van Stellenbosch was genader deur die Gryswater Navorsings-groep, onderleiding van Mnr A. Greyling van BVi Raadgewende Ingenieurs (Edms) Bpk, om ‘n navorsingsmetodiek vir hierdie unieke studie saam te stel. Hierdie navorsingsmetodiek was ook by die Universiteit van Stellenbosch uitgevoer van waar die verwante resultate en gevolgtrekkings van die studie geraportteer was. Die Navorser het ‘n primêre en sekondêre navorsingsmetodiek vir hierdie studie saamgestel wat deur ‘n uitgebreide literatuurstudie voorafgegaan is. Vanuit hierdie literatuurstudie was sleutelfaktore om gryswater-weerstandigheid van asfalt te verbeter, geïdentifiseer. Die primêre-navorsingsmetodiek het die identifisering van graderings- en bindstofkombinasies om die gryswater weerstandigheid van asfalt te verbeter, behels. Die primêre navorsingsmetodiek het uit twee fases bestaan. Fase 1 het uit voginduserende-simulasietoetse (E: MIST) asook indirekte-treksterktetoetse (ITS) bestaan. Treksterkte-verhoudings van hierdie fase het aangedui dat gryswater ‘n beduidende invloed op die sterkte van asfalt in vergelyking met skoon water het. Resultate van Fase 1 het ook aangetoon dat mediumgegradeerde asfalt ‘n verbeterde sterkte teenoor fyn-gegradeerde asfalt na gryswater kondisionering behaal. Die EVA-bindstofbymiddel het ook tot ‘n beduidend beter mengselsterkte na gryswater kondisionering gelei. Fase 2 het uit laboratoriumtoetse met ‘n model mobiele lassimileerder (MMLS) bestaan, asook ITS-toetse op asfaltbrikette wat aan droë (geen water) en nat (gryswater) verkeerstoestande onderhewig was. Resultate vanuit Fase 1 het bygedra tot die keuse van asfaltgraderings- en bindstof-kombinasies wat tydens Fase 2 van die primêre navorsingsmetodiek getoets was. Treksterkte-verhoudings van Fase 2 het nie enige beduidende verskille tussen die medium- en fyngegradeerde asfaltmengsels na gryswater kondisionering getoon nie. Permanente vervormingsresultate het wel aangetoon dat medium-gegradeerde asfalt mengsels met EVA en SBS gemodifiseerde bindstowwe tot laer vervorming gelei het in vergelyking met skoon bindstof kombinasies na gryswater MMLS3 verkeers-kondisionering. ‘n Bindstof bymiddel, genaamd ZycoTherm®, in kombinasie met EVA gemodifiseerde bindstof en Sasobit®, het nie net permanente vervorming verlaag nie, maar ook tot verbeterde asfalt-sterkte gelei. Die resultate van Fase 2 se ITS, permanente vervorming, tekstuur en materiaalverlies was saamgevoeg om beoordelingskriteria saam te stel. Die doel van die kriteria was om ‘n geskikte gryswater-weerstandige asfaltmengsel vir hoë en lae verkeervolumes te identifiseer. Mediumgegradeerde asfaltmengsels kan as ‘n geskikte oplossing dien om ‘n gryswater-weerstandige asfaltmengsel vir hoë verkeervolumes te produseer. Fyngegradeerde asfaltmengels kan as ‘n geskikte oplossing vir lae verkeervolumes dien. Gebaseer op die resultate van die beoordelingskriteria, het die volgende asfaltmengsels beduidende weerstand teen gryswater getoon: . EVA + 1%Sasobit® + Extra Lime (COLTO Medium Deurlopende Gradering) . EVA + Extra Lime (COLTO Medium Deurlopende Gradering) . EVA + 1%Sasobit® (COLTO Fyn Deurlopende Gradering) . EVA + 1%Sasobit® + 0.1%ZycoTherm® (COLTO Fyn Deurlopende Gradering) Na voltooiing van die laboratoriumskaalse MMLS-toetse tydens Fase 2 van die primêre navorsingsmetodiek, was 150 mm diameter asfaltbrikette wat aan verkeer onderhewig was, gebruik vir die uitvoer van ITS-toetse. Die voorbereiding van die asfaltbriket-monsters vir MMLS-toetse het behels die masjinering daarvan deur twee segmente met parallelle koorde en 19 mm mid-ordinate van elk af te saag. Hierdie vereiste het dit moontlik gemaak om nege asfaltbrikette op die toetsbed te installer wat spesifiek vir hierdie doel ontwerp is. Dit het gelei tot die samestelling van ‘n sekondêre navorsingsmetodiek om die invloed van die gemasjineerde asfaltbrikette op die maksimum treksterkte resultaat na ‘n ITS-toets te ondersoek. Die ondersoek was deur middel van lineêr-elastiese eindige-elementmodelle tot stand gebring. Resultate van die sekondêre-navorsingsmetodiek het aangedui dat ‘n verskil van 8% in die maksimum trekstrekte-resultaat in die middel van gemasjineerde en ongemasjineerde asfaltbrikette verwag kan word. Resultate het ook getoon dat die drukspannings in die briket nie beïnvloed was deur masjinering soos hierbo aangedui nie. Insig tot die ontwikkeling van gryswater-weerstandige asfalt word in hierdie verslag aangebied.

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