Basic description of the Dynamic Shear Rheometer (DSR)

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Background

The South African National Roads Agency Limited (SANRAL) and the South African roads industry require the modelling to be developed to the stage where performance evaluation of different seal types in different environments can be carried out, using mechanistic performance modelling and assessment. The damage models for evaluating the performance prediction for road seals (referred to as “seals”) and thin-layer bituminous road surfacings currently included in the South African Pavement Design Method (SAPDM) are insufficiently detailed and need to be developed further. The available mechanistic seal design, developed by Milne (2004), is at prototype stage and needs improvement. The performance of seals is dependent on the material components of the seal and the climate in which the seal is constructed.
The seal structure consists mainly of a combination of bituminous binder and aggregates. Traffic and weather conditions induce stresses in the seal. These stresses dictate the behaviour of the bitumen, and interaction between the aggregate and the bitumen, consequently affecting the lifespan and performance of the seal. #Scope and Extent of the Research This study forms part of the research that has been undertaken under SANRAL South African Road Design System (SARDS) Project in the field of road surfacing seal. Milne (2015) reported on the evolution of this SARDS project and presented the link between different components forming part of the seal system modelling.
The bituminous materials component of the SARDS seal project was investigated through this study. This study focused on the response and damage of seal materials (namely bituminous binder and stone aggregates) as presented in Figure 1-1. The response model investigated only fresh binder (for the newly constructed seal scenario) and aged binder (for the old seal scenario). The intermediary stage where self-healing occurs within the seal was considered to be outside the scope of this study. The damage model was explored only for fresh bitumen. This study was based on the Lifetime Optimisation Tool (LOT) research programme from Delft University of Technology in Netherlands (Huurman, 2007). From LOT research, the Dynamic Shear Rheometer (DSR) was selected as the main laboratory equipment in this study.
The DSR addresses both the loading time and temperature behaviour dependency of bituminous binders (Asphalt Institute, 1997), which are essential parameters in this study. Moreover, the Dynamic Shear Rheometer (DSR) in South Africa motivated the use of the device as the main laboratory equipment in this study. The benefits and limitations identified in using the DSR could help in the testing procedures and results analysis during its implementation stage in the country. In Figure 1-1 the various types of DSR set-ups are illustrated with photo insets and indicated where in the bituminous binder and stone aggregate matrix simulations are performed. In the modelling part of the research, no stone-to-stone contact within the seal was considered. This is because it appears that there is almost always a film of binder between stones, especially in the case of pre-coated stone. During this research, stone cracking and/or breaking under applied loads was not considered as it was assumed that for well-designed seals, the stones were strong enough to prevent breaking under traffic load.

Introduction

The scope of this research highlights the response and fatigue damage characterisation of seal materials. These two concepts will be developed in order to produce the parameters required as input into the seal design which forms part of the pavement design. The “pavement design” concept is well known and is generally described as being constituted of two approaches, namely the empirical method and the mechanistic method, also called the analytical method. Desai (2002) describes mechanistic design methods as being methods based on principles of mechanics, such as elasticity, plasticity and visco-elasticity, while empirical methods are based on experience or index properties (e.g. value of California Bearing Ratio (CBR), limiting deflections).
Paterson (1987), Li and Kumar (2003), and Schram and Abdelrahman (2009) stated that the empirical method uses observed performance from full-scale experiments to determine empirical relationships by regression analysis, while the mechanistic design method identifies the effects of the physical causes of stresses (i.e. loading, environment and material properties) on the performance of the pavement structure. In some cases both approaches are combined, this is called the Mechanistic–Empirical (ME) method. In South Africa, an ME design method has been used since the early 1970s (Maree and Freeme, 1981).

Table of Contents :

• List of Figures
• List of Tables
• List of Abbreviations
• List of Symbols
• List of Units
• 1 INTRODUCTION
  • 1.1 Background
  • 1.2 Problem Statement
  • 1.3 Objectives
  • 1.4 Scope and Extent of the Research
  • References
• 2 LITERATURE REVIEW
  • 2.1 Introduction
  • 2.2 Surfacing Seals
  • 2.3 Seal Components
  • 2.3.1 Bituminous binder
  • 2.3.2 Aggregate
  • 2.4 Seal Design
  • 2.5 Seal Modelling
  • 2.6 Ageing of Bituminous Binder
    • 2.6.1 Background on bitumen ageing
    • 2.6.2 Some bitumen ageing methods
    • 2.6.3 Comments on ageing methods
  • 2.7 Rheology and Visco-elasticity
  • 2.7.1 Introduction
  • 2.7.2 Definitions related to visco-elasticity
  • 2.7.3 Linear visco-elasticity concepts for frequency domain
  • 2.8 Visco-elasticity of Bituminous Material
  • 2.9 Rheological Modelling of Linear Visco-elastic Properties of Bituminous Materials
    • 2.9.1 Construction of master curves
    • 2.9.2 Black space diagrams and Cole-Cole diagrams
    • 2.9.3 Mathematical models
    • 2.9.4 Mechanical models
  • 2.10 Cohesion and Adhesion
    • 2.10.1 Introduction
    • 2.10.2 Adhesion and cohesion mechanisms
    • 2.10.3 Moisture damage effects on adhesion
    • 2.10.4 Conclusion on cohesion and adhesion
  • 2.11 Fatigue of Bituminous Materials
    • 2.11.1 Introduction
    • 2.11.2 Fatigue mechanism
  • 2.12 Summary of Literature Review and Research Recommendations
  • 2.13 References
• 3 EXPERIMENTAL PROGRAMME
  • 3.1 Introduction
  • 3.2 Bituminous Materials Used for the Experiment
  • 3.3 Basic description of the Dynamic Shear Rheometer (DSR)
    • 3.3.1 Bitumen frequency sweep response test using the DSR
    • 3.3.2 DSR testing for cohesion fatigue damage and adhesion fatigue damage tests
    • 3.3.3 Special DSR setups for cohesion fatigue damage test
    • 3.3.4 Special DSR setups for adhesion fatigue tests
  • 3.4 Sample Preparation and Conditioning
    • 3.4.1 Water conditioning by vacuum vessel
    • 3.4.2 Ageing by Q-SUN
  • 3.5 Development of Testing Procedures for Cohesion and Adhesion Fatigue Damage
    • 3.5.1 Stabilisation of testing temperature in the chamber
    • 3.5.2 Choice of testing parameters
    • 3.5.3 Choice of testing mode: strain controlled vs. stress controlled
    • 3.5.4 Impact of changes in DSR geometry configuration on the test output
    • 3.5.5 Pure shear test mode vs. combined shear and normal stress test mode
    • 3.5.6 Choice of binder film thickness between stone columns in the adhesion test
    • 3.5.7 Repeatability of tests
    • 3.5.8 Binder fatigue related to change in sample radius
    • 3.5.9 Use of parallel plates for cohesion fatigue damage test
  • 3.6 Testing Approach Adopted
  • 3.7 Testing Protocols
    • 3.7.1 Bitumen frequency sweep response protocol
    • 3.7.2 Cohesion fatigue damage test protocol
    • 3.7.3 Adhesion fatigue damage test protocol
  • 3.8 Summary
  • References
• 4 RESULTS, INTERPRETATION AND MODELLING CONCEPT OF COHESION AND ADHESION FATIGUE DAMAGE
  • 4.1 Introduction
  • 4.2 Bitumen Response Outcome
    • 4.2.1 Results of the mathematical models
    • 4.2.2 Mechanical model results
    • 4.2.3 Comparison between different models
  • 4.3 Cohesion and Adhesion Fatigue Damage Outcome
  • 4.4 End–life Damage Principle
  • 4.5 Principle of Damage During-life Period
  • 4.6 Summary
  • References
• 5 RHEOLOGICAL RESPONSE, COHESION AND ADHESION FATIGUE DAMAGE MODELS OF BITUMINOUS ROAD SEAL MATERIALS
  • 5.1 Introduction
  • 5.2 Models Based on Response Data
    • 5.2.1 Principle of development of ageing model
    • 5.2.2 Ageing model of a seal’s bitumen
  • 5.2.3 Discussion of the ageing model
  • 5.3 Fatigue Damage Modelling
    • 5.3.1 Background to fatigue life
    • 5.3.2 Fatigue damage model of cohesion and adhesion using the end-life principle
    • 5.3.3 Fatigue damage model of cohesion and adhesion in the during-life period
  • 5.4 Summary
  • References
• 6 INPUT PARAMETERS FOR SEAL MODELLING AND SEAL DESIGN
  • 6.1 Introduction
  • 6.2 Use of Rheological Response, Cohesion and Adhesion Fatigue Damage Parameters
  • 6.3 Summary
  • References
• 7 CONCLUSION AND RECOMMENDATIONS
  • 7.1 Conclusion
  • 7.2 Recommendations
  • REFERENCES

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