Warm mix asphalt vs. hot mix asphalt : flexural stiffness and fatigue life evaluation

Van den Heever, Johann (2014-04)

Thesis (MScEng)--Stellenbosch University, 2014.

Thesis

ENGLISH ABSTRACT: The UNFCCC (United Nations Framework Convention on Climate Change), enabled by the Kyoto Protocol, set enforced responsibilities on industrialised countries to reduce the amount of emissions (greenhouse gases) produced. This global call for the reduction of greenhouse gas emissions ensured that the manufacturing sector commit to emission reduction. The asphalt industry has embarked on a quest to find alternative methods of producing and constructing asphalt mixes which will release less greenhouse gasses into the atmosphere. These new methods include the reduction in production and construction temperatures which in turn will reduce the amount of greenhouse emissions produced. These new methods introduced the concept of warm mix asphalt (WMA) to the alternative hot mix asphalt (HMA). To produce a WMA mix at lower temperatures the binder needs to be in a workable state so to effectively coat the aggregate and produce a good quality mix. WMA technologies have been developed to enable production of mixes at lower temperatures (effectively reducing emissions) whilst retaining the required binder viscosity and properties needed to produce a quality mix. The question which needs to be answered is whether the performance of these WMA mixes can compare with that of HMA mixes. In this study several WMA mixes (with different WMA technologies) are evaluated against their equivalent HMA mixes in terms of fatigue life and flexural stiffness. Phase angle results were also considered. Flexural stiffness is a mix property which is dependent on loading time and temperature. It is used to measure the load spread ability of a mix and also influences fatigue behaviour. Fatigue cracking occurs in the material as a result of repeated cyclic loading. The evaluation and analysis conducted in this study show that WMA mixes can compare favourably and even exceed that of HMA mixes in certain cases, although some WMA mixes resulted in lower fatigue life or flexural stiffness than its corresponding HMA mixes, which could be attributed to differences in mix components and variables. In this study a literature study, methodology, laboratory test results, a comparison of mix results and conclusions and recommendations are made.

AFRIKAANSE OPSOMMING: Die UNFCCC (United Nations Framework Convention on Climate Change) was in staat gestel deur die Kyoto Protocol om verantwoordelikhede op geïndustrialiseerde lande te forseer om die hoeveelheid van nadelige kweekhuisgasse wat geproduseer word te verminder. Hierdie globale oproep tot die vermindering van kweekhuisgasse verseker dat die vervaardigingsektor hulself verbind tot emissie vermindering. Die asfalt industrie het begin met 'n soektog na alternatiewe metodes van vervaardiging en die bou van asfaltmengsels wat minder kweekhuisgasse sal vrystel in die atmosfeer. Hierdie nuwe metodes sluit die vermindering in produksie en konstruksie temperature in wat op sy beurt die hoeveelheid kweekhuisgasse geproduseer verminder. Hierdie nuwe metodes het die konsep van warm mengsel asfalt (WMA) bekendgestel teenoor die alternatiewe ‘hot’ mengsel asfalt (HMA). Om ‘n WMA mengsel te produseer by laer temperature, moet die bindmiddel in 'n werkbare toestand wees om die aggregaat heeltemal te bedek en 'n goeie gehalte mengsel te produseer. WMA tegnologie is ontwikkel om die produksie van mengsels teen laer temperature te realiseer (vermindering die uitlaatgasse), terwyl die vereiste bindmiddel viskositeit en eienskappe wat nodig is om 'n kwaliteit mengsel te produseer behou word. Die vraag wat beantwoord moet word, is of die prestasie van hierdie WMA mengsel kan vergelyk word met dié van HMA mengsel. In hierdie studie is 'n paar WMA mengsels (met verskillende WMA tegnologie) geëvalueer teen hul ekwivalent HMA mengsels in terme van vermoeiing en buig styfheid. Fase hoek resultate is ook in ag geneem. Buig styfheid is 'n mengsel eienskap wat afhanklik is van die laai tyd en temperatuur. Dit word gebruik om die las verspreiding vermoë van 'n mengsel te meet en beïnvloed ook vermoeiing gedrag. Vermoeidheid krake kom voor in die materiaal as gevolg van herhaalde sikliese laai. Die evaluering en ontleding in hierdie studie toon dat WMA mengsels goed vergelyk en selfs in sekere gevalle meer as dié van HMA mengsels, hoewel sommige WMA mengsels laer vermoeidheid lewe of buig styfheid as die ooreenstemmende HMA mengsels gewys het, wat toegeskryf kan word tot verskille in mengsel komponente en veranderlikes. In hierdie studie word 'n literatuurstudie, metodiek, laboratorium toets resultate, 'n vergelyking van die mengsel resultate en gevolgtrekkings en aanbevelings gemaak.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/86439
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