Nonlinearity of Repeated Creep and Recovery Binder Test and Relationship with Mixture Permanent Deformation

Abstract

It is recognized that the Superpave^® binder rutting parameter (G^*/sinδ) is not sufficient to evaluate binder contribution to asphalt mixture rutting. As a result of the NCHRP 9–10 project, a new dynamic shear rheometer test was introduced with promising results: repeated creep and recovery (RCR). For simplicity, the original RCR creep stress was 25 Pa so that the binder would stay in the linear range. However, there is evidence that stresses under traffic loads are high enough to make the binder reach the nonlinear range. This paper was prepared to cover the stress dependency of binders in the RCR test and the relationship with mixture performance. Eight different binders, modified and unmodified, were compared in the stress dependency. The relationship between binder and mixture performance was studied with mixtures prepared with two kinds of aggregates and seven different binders. Results show that the binder stress sensitivity varies significantly between binders on the basis of modification type and testing temperatures. Results of the mixture repeated creep show significant effects of modifier type and good correlation with results of the RCR of binders. For stresses until 10,000 Pa, the correlation between RCR and mixture permanent deformation is good in regard to the stress level selected. It was also noticed that binder samples that were able to withstand high levels of stress in the RCR test without collapse provided the mixtures with a lower amount of permanent deformation. The stress sweep using cyclic loading to measure G^* relates well to the stress sensitivity measured with RCR.