Characterisation of fatigue performance of selected cold bituminous mixes

Mathaniya, Twagira Elias (2006-04)

Thesis (MScEng) -- Stellenbosch University, 2006.

Thesis

ENGLISH ABSTRACT: The use of cold mixes (bitumen emulsion and foamed bitumen mixes) in road rehabilitation and construction is gaining favour globally due to its advantage of conservation of environment, resources, and money. Cold bituminous treated materials exhibit to a certain degree aspects of basic characteristics of granular materials, cement-treated materials and hot mix asphalt depending on the mix proportion of bitumen, mineral aggregates and active filler. Where high binder contents are used to improve strain-at-break (flexibility) and fatigue performance of these mixes, the material approaches loading-frequency and temperature dependency, i.e. visco-elastic behaviour, similar to that of hot mix asphalt. An understanding of the strain-at-break behaviour and fatigue relationship of cold mixes in a pavement layer, therefore, is of considerable importance to ensure correct mix design and analysis of the cold mix layer in a pavement structure. The main objective of this thesis is to characterize the fatigue performance of selected cold bituminous treated materials, by providing a fundamental understanding of the fatigue properties and its link to strain-at-break properties and visco-elastic behaviour associated with dependency of temperature and rate of loading on the performance of these mixes. The study investigates the fatigue, strain-at-break, and stiffness modulus (master curve) properties of the different materials types, i.e. virgin crushed limestone, and reclaimed asphalt pavement (RAP) millings blended in two different proportions. Either the limestone or the RAP was selected as the dominant portion, i.e. 75% by mass. These blends were treated with various bitumen contents of either bitumen emulsion or foamed bitumen. The influences and effect of active filler in these mixes were investigated too; 1 % cement was added to the 75% limestone blends. The characterization of these mixes fatigue properties, as well as strain-at-break and flexural stiffness (master curve) properties were developed using a four-point beam testing apparatus. The apparatus is believed to provide an insight on fatigue failure mechanism of specimen by performing flexing tests in the form of an alternating stress or strain of certain amplitude. It was found in the investigation that the fatigue test under controlled displacement mode of these mixes show that the fatigue life is dependent on the loading rates. On a log-log scale plot, linear fatigue functions are obtained. The foamed bitumen and emulsion mixes without active filler (cement) show no significant difference in fatigue life at high strain levels. However with the addition of small quantity of cement (1 %) a notable shift in the fatigue line for the foam mixes occurs with an increase in fatigue life compared with that of the emulsion mixes. When emulsion or foam is used for the treatment of the mixes with higher percentage of RAP a decrease in fatigue life occurred. The significant differences occurred in the strain-at-break properties of selected mixes indicate that the test protocol needs further development to provide a reliable link of this parameter to fatigue performance. Further more it cannot define accurately the flexibility behaviour of the cold mixes but provides some indication of flexibility which can be used in the mix design process. The flexural stiffness response of the selected mixes however proves to be both temperature and loading rate dependent.

AFRIKAANSE OPSOMMING: Die gebruik van koue mengsels (bitumen emulsies en geskuimde bitumen mengsels) in padoppervlakrehabilitasie en -konstruksie, wek tans wereldwyd belangstelling as gevolg van die voordele wat dit inhou in die vorm van finansiele besparings en die behoud van hulpbronne en die omgewing. Koue bitumineus-behandelde materiale vertoon tot 'n sekere mate die basiese eienskappe van granulere materiale, sement-behandelde materiale en warmgemengde asfalt afhangende van die verhouding waarin die bitumen, mineraalaggregate en aktiewe vulstof gemeng word. Wanneer 'n hoe inhoud van bindstof gebruik word om die reck-by-breek (buigsaamheid) en die vermoeingseionskappe van hierdie mengsels te verbeter, vertoon die materiale 'n belastingsfrekwensie en temperatuur afhanklikheid (visko-elastiese gedrag), wat benaderd ooreenstem met die van warmgemengde asfalt. 'n Beier begrip van die reck-by-breek gedrag en die vermoeiings gedrag van koue mengsels in die plaveisel strucktuur is dus van groot belang om die korrekte mengselontwerp en analise van die koue mengsels in die plavaiselstruktuur te verseker. Die hoofdoelwit van hierdie studie is om die vermoeiings gedrag van geselekteerde koue bitumeneusbehandelde materiale te karakteriseer deur 'n fundamentele begrip van die vermoeiingeienskappe, en die effek van die reck-by-breek eienskappe en die visko-elastiese gedrag op die vertoning van hierdie mengsels te verskaf. Die studie ondersoek die vermoeiing, reck-by-breek, en styfheidsmodulus (meesterkurwe) eienskappe van die materiaaltipes, bestaande nuut-vergruisde kalksteen en herwinde asfalt padoppervlak skerwe wat gemeng is in twee verskillende verhoudings. Kalksteen, 6f die padoppervlak skerwe was gebruik in oormaat, d.w.s 75% van die totale massa, waarna verskeie hoeveelhede bitumen in die vorm van 6f bitumen emulsie 6f geskuimde bitumen daarby gevoeg is. Die invloed en effek van aktiewe vulstof in hierdie mengsels was ook ondersoek. Vir hierdie studies was 1 % sement toegevoeg tot die 75% kalksteen mengsels. Die karakterisering van die vermoeiingseienskappe, asook die reck-by-breek en die buigingstyfheid (meesterkurwe) erenskappe van hierdie mengsels, was ontwikkel deur gebruik te maak van 'n vierpunt balk toetsingsapparaat. Die apparaat verskaf 'n beter begrip van die meganisme van monsters deur 'n buigingstoets in die vorm van 'n alternerende druk of spanning van 'n sekere amplitude uit te voer. In die ondersoek was daar gevind dat vermoeiings tretse van hierdie mengsels in 'n beheerde verplasingsmodus toon dat vermoeiingssleeftyd afhanklik is van die belastingsfrekweusie. Liniere vermoeiingsfunksies was dus op 'n log-log plot verkry. Die geskuimde bitumen en emulsie mengsels sender aktiewe vuller (sement) wys geen beduidende verskil in vermoiingsleeftyd ten opsigte van die binderstofipe by hoe vlakke van belasking nie. Byvoeging van 'n klein hoeveelheid sement (1%) veroorsaak wel 'n merkbare skuif in die vermoeiingslyn van die skuimmengsels in vergelyking met die emulsiemengsels waarby die vermoeiingsleeftyd verleng word. Wanneer emulsies of skuim bitume gebruik word vir die behandeling van die mengsels met hoer persentasies herwinde asfalt padoppervlak, het 'n verkorting in vermoeiingsleeftyd plaasgevind. Die verskille in reck-by-breek eienskappe van die geselekteerde mengsels toon dat die toetsprotokol verdere ontwikkeling vereis om 'n betroubare skakel met vermoeiingsgedrag te verskaf. Dit verskaf wel egter 'n oorweging van buigsaamheid in die samestelling van mengsels. Die buigveerkragsmodulus van die geselekteerde mengsels het bewys dat dit temperatuur- en beladingstempo afhanklik is.

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