Developing the multiple stress–strain creep recovery (MS-SCR) test

Mahmoud Elnasri,Gordon Airey,Nick Thom

doi:10.1007/s11043-018-9387-y

Mahmoud Elnasri, Gordon Airey + Show 1 more

Open Access

https://doi.org/10.1007/s11043-018-9387-y

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Abstract

While most published work from Europe has been concerned with evaluating binders’ resistance to rutting based on their stiffness (deformation resistance), work originating in the US has mainly been concerned with ranking binders based on their recoverability in a multiple stress form. This paper details the design of a new modified multiple stress–strain creep recovery (MS-SCR) test. The test is designed to evaluate binders’ rutting resistance based on two rutting resistance mechanisms: stiffness and recoverability. A preliminary investigation is presented in this paper followed by details of the design of the new modified test. A 40/60 penetration grade bitumen and bitumen-filler mastics prepared with three filler concentrations (35%, 50%, and 65% filler content by mass of mastic) were tested. In addition, two polymer modified bitumens (PMBs) using the same base bitumen type were examined for validation. Two parameters are introduced to characterise the short and long recovery in the new test. In terms of stiffness, the test allows the behaviour of binders at different stress levels and loading cycles to be studied and produces a new parameter that can quantify the degree of modification. Finally, a relationship between nonlinearity and normal force in the test was investigated.

Highlights

The resistance of an asphalt mixture to permanent deformation is highly dependent on the properties of its binder
The objective of the paper is to design a new Multiple Stress-Strain Creep Recovery (MS-SCR) test, able to distinguish between the two rutting resistance mechanisms; stiffening and recoverability which can fit all binder types
2.4 Design of multiple stress-strain creep recovery (MS-SCR) The literature review above revealed that the multiple stress creep recovery (MSCR) test is the most recent advancement in terms of a rutting evaluation test for binders

Summary

Introduction

The resistance of an asphalt mixture to permanent deformation (rutting) is highly dependent on the properties of its binder. Empirical tests (i.e. penetration and softening point) were used to evaluate the resistance of the binder to rutting. This evaluation has shifted from empirical to more fundamental rheological tests using the dynamic shear rheometer (DSR) to attain detailed characterisation and specific permanent deformation results. Different rheological testing protocols and parameters are being developed to meet the demand for correct bitumen rutting evaluation methods. The failure of the first rheological Superpave permanent deformation evaluation parameter (G*/sin δ), with regard to polymer modified bitumens (PMBs), increased the awareness of the need for a more appropriate testing procedure and parameter. A detailed review of problems associated with G*/sin δ can be found in (Delgadillo et al, 2006b), summarised as follows: The applied loading during the test is fully reversible which does not simulate the actual loading in the real pavement (real loading reaches a maximum and returns to the zero level)

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