Asphalt bound mixtures have been put to diverse uses. The complicated nature of the material and the demanding conditions under which it is used preclude complete solutions to questions on load bearing capability under field conditions. In proportion to the quantity of its usage and in acknowledgment of modeling complexity, the material has been interrogated by many researchers using a variety of mechanical tests, and a plethora of linear viscoelastic models have been developed. Most models are intended to account for specific classes of problems. This work addresses the conspicuous absence of systematic documentation of normal forces generated as a result of shear. The normal force generated during simple shear is a clear indication of the nonlinear nature of the material. The effect of fillers (hydrated lime and limestone), air voids, aggregate gradation, asphalt source and step loading on normal force generation during torsion is experimentally investigated. Based on experimental evidence, a non-linear thermomechanical model for sandasphalt mixtures based on the idea of multiple natural configurations is developed. The model accounts for the fact that the mixture has a natural configuration (stressfree configuration) which evolves as it is subjected to loads. Assumptions are made regarding the manner in which the material stores and dissipates energy. A key assumption is that among the various constitutive relations possible, the one that is chosen is the one that maximizes the rate of entropy production. The model that is developed accounts for the anisotropic nature of the response. The experimental results show that asphalt bound mixtures generate significant normal forces even at low rotation rates. The source of asphalt, aggregate gradation, fillers and air voids have a pronounced effect on normal stress generation. The model is corroborated against data from torsion experiments.

[pt] Esse trabalho propõe investigar medidas de tensão normal para materiais com tensão limite de escoamento. O reômetro ARES-G2 da TA Instruments de deformação controlada foi utilizado para estudar três diferentes materiais elastoviscoplásticos. Um procedimento experimental simples e efetivo foi desenvolvido para obter resultados repetitivos de medidas em regime permanente e transiente. Respostas interessantes foram obtidas mediante comparação dos resultados destes fluidos. Para a dispersão de Carbopol e o gel de cabelo, os resultados entre os testes transientes e em regime permanente foram bastante similares. Porém, o mesmo não foi observado para a emulsão altamente concentrada. Além disso, variáveis como N1, phi1, gamaponto, tau, G,G,eta, tauy,sigmas, foram exploradas para um melhor entendimento do estado de tensão desses materiais. Ademais, as tensões normais medidas foram extremamemente mais altas que as tensões cisalhantes, quando o material foi submetido à baixas taxas de cisalhamento. Para altas taxas de cisalhamento, diferentemente dos outros dois fluidos, a emulsão altamente concentrada apresentou valores de tensão normal que eram mais baixos do que os de tensão cisalhante. Por fim, em contraste com a maioria dos resultados encontrados na literatura, apenas tensões normais negativas foram obtidas para os materiais estudados. / [en] This work proposes to investigate normal stress measurements for yield stress materials. Using an ARES-G2 TA Instruments strain-controlled rheometer, three different elastoviscoplastic materials were studied. A simple but effective experimental procedure was developed to obtain repetitive results for both steady-state and transient measurements. These tests were put to comparison, and interesting results were obtained. For the Carpobol dispersion and the commercial hair gel, transient and steady-state results were quite similar. Although, the same was not observed for the highly concentrated emulsion. Also, variables such as N1, phi1, gamaponto, tau, G,G,eta, tauy,sigmas were explored to better understand the stress state of these materials. Furthermore, normal stresses were significantly higher than shear stresses, while all materials were submitted to low shear rates. For high shear rates, different from the other two fluids, the highly concentrated emulsion displayed normal stress values that were lower than shear stress ones. Finally, in contrast with most results found in literature, only negative normal stress results were obtained for the materials studied.