Rotationsviskosimeter, RVB

Detta är en Kandidat-uppsats från Lunds universitet/Utbildningar i Helsingborg

Sammanfattning: To most people bitumen is an unknown material although it is the most important ingredient in asphalt pavements, something that everyone knows and uses every day. By merely distilling crude oil a substance is produced with unique properties and durability, which could not have been produced by synthetic means, at least not in those quantities used. The production is not that simple and the raw material must be chosen carefully. Soft qualities are for cold climates and hard ones are for hot areas. This is due to the fact that the bitumen stiffness depends on the temperature. Bitumen binds the aggregate together and jointly they constitute road asphalt pavements. To achieve the desired quality it must be mixed and laid down in the best way possible. Consequently, stiff bitumen resulting in hard asphalt pavements must be heated more than the soft qualities. In order to figure out what temperature is required the viscosity of the bitumen is measured. It is determined at different temperatures and the one providing the right consistency of the asphalt mix is chosen. In recent decades, new methods for measuring viscosity have been developed, which makes the measurements less labor intensive and more productive. The problem is that the old methods are incorporated in the regulations and are well-known to most operators. It creates an inertia to change. In an attempt to increase the pace of this transformation this thesis is launching an old-school method, called rotational viscometer, manufactured by Brookfield, RVB in short. The equipment has undergone major improvements in recent years. To demonstrate the usefulness of this RVB-technique three different types of bitumen were investigated, 70/ 100 which is a bitumen of standard quality, Sas 85-3 which is a bitumen containing Sasobit wax and PMB, a widely used polymer modified bitumen. The viscosity was determined at various stages, virgin before mixing, after laying down on the road and at the end of the asphalt pavement life time. The latter two stages were simulated with two heating methods, RTFOT and PAV. Bitumen and asphalt change over the years and eventually loses its elasticity and cohesiveness and must be repaired or replaced. The expression is that the pavement has aged. These processes can be illustrated by RVB and it provides a basis for proper grades to be selected. The results must be presented in a way easy to survey and understand. For this purpose, another old-school tool is taken up again: the Heukelom BTDC, Bitumen Test Data Chart, which was launched more than 40 years ago. The results of RVB measurements are ideal to be presented in the chart, which has now been digitized for modern numerical processing. This synergy has been developed at Lund University in five theses since 2011, besides this present work. The survey shows that RVB in a credibly manner is capable of measuring the viscosity of three rheologically very different binders, so that their properties can be compared and evaluated as components of asphalt pavements. The Sasobit wax makes binder stiffer when it crystallizes, while it adds non-Newtonian properties and somewhat poorer low temperature properties. The suitable qualities of polymer modified bitumen come at the cost of high manufacture temperatures, as indicated by viscosity measurements. The aging method RTFOT correlates well with what is measured in asphalt after being mixed and laid on the road. In combination with PAV it reflects what is found in old reclaimed asphalt. The precision of the measurement technique is important and it is studied in one of the job sections. The accuracy of the RVB-method largely complies with the requirements of the American ASTM and keeps below the allowable values in European EN. This is concluded after having varied times, weighed amount of sample and shear rate, some parameters that might influence the results. The RVB technology replaces in one single measurement three standardized methods, Ring and Ball, dynamic viscosity and kinematic viscosity. This saves a lot of time and money. The technique is not only adequately repeatable but also adds information beyond what the old methods offer, namely an overall picture in the Heukelom chart. The measurements can also be monitored and controlled over the internet, which allows for time - and cost-saving labor division at the laboratory. These findings should be sufficient to give the RVB technology a central role to play in future quality assessments of bitumen and modified binders for asphalt pavements.

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