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Title of Thesis

Impact of Hot Mix Asphalt Properties on it Permanent Deformation Behavior

Author(s)

Imran Hafeez

Institute/University/Department Details
Department Of Civil Engineering, Faculty Of Civil & Environmental Engineering / University Of Engineering And Technology, Taxila
Session
2009
Subject
Civil Engineering
Number of Pages
169
Keywords (Extracted from title, table of contents and abstract of thesis)
Hot Mix, Asphalt, Properties, Deformation, Behavior, Dynamic, Shear, Rheometer, uniaxial

Abstract
Over the past twenty years; road traffic (both passenger and freight) has grown significantly and loading is progressively getting worse due to the introduction of newer and more powerful trucks with heavier wider bodies in Pakistan. Consequently, premature rutting in the form of shear flow in flexible pavements has been observed during high ambient temperatures. National Highway Authority (NHA), Pakistan has been facing serious threats like, frequent pavement failures, poor riding quality and high maintenance cost. Modifications of Asphalt cement with polymers and rigid pavement design trends, being the end solutions, have increased the construction cost, even more than four times than that of conventional design. In order to cater for the growing axle load demand and to increase the performance of asphalt concrete mixes, true prediction and accurate estimation of probable behavior of mixes need to be investigated.
A comprehensive laboratory study was carried out using NHA aggregate gradation Class “A” for asphaltic wearing course, which has commonly been used in the field. The main objective of the research work was to evaluate the effects of temperature and loading on the permanent deformation behavior of mixes, designed with the same aggregate gradation and three commonly available asphalt cement types (A.C). Two gradations i.e. “01” and “02”, within the envelope of the same gradation, were chosen for this study. Three asphalt cement (A.C.) types i.e. two neat A.C with penetration grade “60/70”, “40/50” and one modified A.C. (base “60/70” pen. grade with Elvaloy Terploymer) were selected. Six mixes ranging from finer to coarser aggregate gradation were therefore designed at optimum filler contents, in order to get better mix cohesion, resistant to rutting and to improve serviceability. Three percentages of mineral fillers (i.e. 2.4%, 3.4%. & 4.4%) were trialed in order to determine the optimum filler content for asphalt mixes.
Mix design properties i.e. optimum asphalt content, percentage air voids, voids in mineral aggregates, voids filled with asphalt, flow and stability were determined using Marshall Method of Mix Design. Asphalt cement consistency i.e. penetration grade, ductility, softening point and rheological properties i.e. phase angle & complex shear modulus were also measured. The temperature influence on rheological properties were determined at constant frequency of 10 Hz using Dynamic Shear Rheometer.
Two performance tests i.e. uniaxial repeated loading strain & wheel tracking tests were chosen to measure the permanent deformation of asphalt mixes. Relationship between rutting and factors effecting rutting were developed. Domains of intercept and slope coefficient and permanent deformation coefficients alpha (α) and mu () were also determined. New relationships have been developed to predict the impact of Hot Mix Asphalt properties on its permanent deformation behaviour. It has been revealed that mixes with coarser gradation and polymer modified asphalt showed better resistance against rutting. Permanent deformation coefficients, such as α and indicate influence of mix properties on mix rut potential. It was further observed that temperature has no effect on α but influences significantly on .
This study presents relationships developed to correlate temperature and rut values of mixes, tested under wheel tracker (WT). It also presents a comparison between uni-axial repeated load strain tests (or repeated creep test) and wheel tracker tests in terms of regression constants, shift factors and a correlation between both the test methods. Intercept coefficient varies in a narrow range. Based on intercept coefficient, uniaxial repeated load strain test (repeated creep test) did not provide clear ranking of mixes at specified temperatures and stress conditions. The slope of data line between both the tests reduces with increase in temperature and stress levels, which means permanent deformation increases with an increase in temperature and stress. An average value has been determined for approximate shift of creep test data to WT test data.
Furthermore a statistical estimation of Mechanistic-Empirical Model has been formulated that relates plastic to elastic strain ratio with different variable that influenced in the mix rut development. Using 54 variables, comprising six mixes designed at low asphalt contents, three temperatures (25, 40 and 550C) and three stress levels (100, 300 and 500 kPa) under repeated load test, a mathematical model was developed to assess the magnitude of plastic to elastic strain ratio. It was observed that plastic to elastic strain ratio is a function of number of load repetitions, temperature, stress levels, shear complex modulus of asphalt cement and aggregate gradations respectively. Despite few limitations i.e. single source of aggregate, single method for mix design, two test methods, certain parameters that help to estimate the permanent deformation in the asphalt layers of flexible pavements were successfully captured in the model.
Keywords: Flexible Pavement, Hot Mix Asphalt, Uniaxial Repeated Loading, Wheel Tracker, Permanent Deformation.

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2,876 KB
S. No. Chapter Title of the Chapters Page Size (KB)
1 0 CONTENTS

 

viii
115 KB
2

1

INTRODUCTION

1.1 Background
1.2 Problem Statement
1.3 Research Objectives
1.4 Research Methodology
1.5 Organization

2
125 KB
3 2 LITERATURE REVIEW

2.1 Introduction
2.2 Permanent deformation (rutting) of Asphalt Mixes
2.3 Influence of Asphalt Mixture Properties on Rutting
2.4 Influence of Aggregates Properties on Rutting
2.5 Influence of Mineral Filler’s Properties on Rutting
2.6 Influence of Asphalt Cement Properties on Rutting
2.7 Stress Strain Behavior of Asphalt Materials
2.8 Resistance to Permanent Deformation of HMA
2.9 Permanent Deformation Prediction Models

9
634 KB
4 3 MATERIAL CHARACTERIZATION

3.1 Introduction
3.2 Aggregates for Asphalt Mixtures
3.3 Characteristics of Asphalt Cement
3.4 Dynamic Shear Rheometer (DSR)

34
243 KB
5 4 MIX DESIGN METHODS

4.1 Introduction
4.2 Combined Grading of Aggregates
4.3 Asphalt Mixtures
4.4 Mix Design Properties
4.5 Mineral Filler Optimization
4.6 Asphalt Mixtures Volumetric

50
136 KB
6

5

UNIAXIAL REPEATED LOAD STRAIN TEST (URLST)

5.1 Introduction
5.2 Universal Testing Machine (UTM-5P)
5.3 Uniaxial Repeated Load Strain Test (URLST)
5.4 Test Conditions
5.5 Testing Methodology
5.6 Discussion of URLST Results
5.7 Resilient Strain
5.8 Summary of Results

60
235 KB
7

6

WHEEL TRACKING TEST

6.1 Introduction
6.2 Wheel Tracking Device
6.3 Specimen Preparation on Roller Compactor
6.4 Discussion of Results

72
594 KB
8

7

RESULTS AND DISCUSSIONS

7.1 Introduction
7.2 Regression Coefficients
7.3 Permanent Deformation Coefficient
7.4 Comparisons of Results to Other Researchers
7.5 Regression Analysis
7.6 Ranking of Mixes using Intercept Coefficient
7.7 Shift Factor Computations
7.8 Correlations Between URLST and WT Test
7.9 Summary

83
488 KB
9

8

MODELING THE PERMANENT DEFORMATION PROPERTIES OF HOT MIX ASPHALT

8.1 Introduction
8.2 Data Analysis and Model Development

102
567 KB
10

9

CONCLUSIONS AND RECOMMENDATIONS

9.1 Introduction
9.1 Conclusions
9.2 Recommendations for Future Study

112
129 KB
11

10

REFERENCES & ANNEXURE

 

114
712 KB