Abstract
The use of asphalt materials is increasing due to their excellent adhesive and waterproof properties and their relatively low costs. However, a technological assessment of asphalt as civil engineering and building materials in terms of engineering properties is still very limited. Varicus practical applications such as asphalt membranes, sandwiches and slip layer systems etc. have been made on the basis of trial and error or experimental data rather than on the basis of a systematic or theoretical assessment. To describe the engineering properties in rheological terms, it is very important, as a basic approach, to systematize stress relaxation and creep phenomena, adding them to the many previous reports concerned with empirical data on asphalts and mixes.
The aim of this study is to indicate the rheological properties of asphalt materials in practical engineering applications by the systematic analysis of stress (or strain) relaxation and creep behaviour. Fig. 2 shows a rheological curve for asphalt utilization. Stress (or strain) relaxation and creep phenomena are translated into constituents from elastic to viscous through delayed elastic components depending upon the conditions of loading time and temperature.
Creep tests were carried out using a Sliding Plate Rheometer (Fig. 3) and Tube Viscometer (Fig. 5) to identify and quantify the above components (Figs. 4-7). These test procedures are considered suitable since they yield typical results that coincide with the curves of Stiffness (S) and Loading time (t) at constant temperature obtained from the nomograph by Van der Poel (Fig. 1). The test results of total strain (ε) are also analyzed and separated into individual strains of elastic (εe/ε), delayed clastic (εd/ε) and viscous (εv/ε) components, as shown in Figs. 8-10. Under constant temperature and long loading conditions, the product of loading time and stiffness approaches a constant value as follows,
5°C (Pen. 120, TR&B 40.0°C, P.I.-2.0),
3η=limt→∞[S•t]=3×102kg•S/cm2
(Pen. 90, TR&B 47.0°C, P.I. -0.5),
3η=limt→∞[S•t]=103kg•S/cm2
10°C (Pen. 90, TR&B 47.0°C, P.I. -0.5),
3η=limt→∞[S•t]=2×102kg•S/cm2
(Pen. 47, TR&B 68.0°C, P.I. +2.3),
3η=limt→∞[S•t]=1.5×104kg•S/cm2
20°C(Pen. 90, TR&B 47.0°C, P.I. -0.5),
3η=limt→∞[S•t]=2×10kg•S/cm2
(Pen. 47, TR&B 68.0°C, P.I.+2.3),
3η=limt→∞[S•t]=1.5×103kg•S/cm2
When describing a stress/strain relationship, the relative contributions to the total strain of the elastic, delayed elastic and viscous components will depend on temperature, loading time, and type of asphalt material. For a given asphalt material these effects are independent of temperature conditions. With temperatures above 10°C there will be little contribution from the elastic component. At short loading times the delayed elastic component will predominate whereas at long loading times the viscous component will predominate.
It is thus possible to evaluate the deformation properties of asphalt in engineering terms using the creep test and also to classify asphalt materials according to their engineering properties under different temperatures and loading times.
