Modelling of Asphalt Mixes under Long Time Creep at Low Temperatures

Abstract

Proper description of asphalt mixtures behavior under long time load is one of the most important factors in analyses of strain and stress relations at low temperatures both from traffic and environmental loads. For example different models of thermal stress accumulation require different approaches of description of asphalt concrete. But in all cases it is required to describe its behavior under long time loading, which in some cases may be even longer than 10 000seconds.This paper presents advantages and disadvantages of three different models used for description of the asphalt mixes behavior in low temperatures. The authors have chosen three following approaches: generalized models, which describe asphalt mixtures using one parameter – the stiffness modulus – designated for a specific temperature and time of loading; rheological models (represented by Burgers rheological model), which describe asphalt mixtures using two or more parameters at a discrete range of temperature but at a continuous range of time of loading and master curves models which describe asphalt mixtures in a continuous range of both temperature and time of loading.Parameters of presented models were obtained from laboratory three-point bending creep tests conducted on different asphalt mixtures: high modulus asphalt concretes (HMAC), conventional asphalt concretes (AC), stone matrix asphalt (SMA) and porous asphalt (PA). The bending creep tests were conducted at three temperatures: 0°C, -10°C and -20°C for the time of loading of 2400seconds according to the procedure developed at Gdansk University of Technology. In this study the authors presented parameters only for HMAC.Commonly used models assume that asphalt mixture is linear viscoelastic and thermorheologically simple material. Authors found that those assumptions were not always valid for long time loads at low temperatures, especially for asphalt mixes made with hard grade bitumen.As the conclusions the authors presented a comparison of parameters calculated for each analysed model, advantages and disadvantages of each model and the impact of a chosen model on asphalt pavement analyses at low temperatures.