Mix design of foamed bitumen mixtures

  • View
    212

  • Download
    0

Embed Size (px)

Text of Mix design of foamed bitumen mixtures

  • 8/21/2019 Mix design of foamed bitumen mixtures

    1/40

    Table of Contents1 Introduction .................................................................................................................................... 1

    1.1 Problem statement .................................................................................................................1

    1.2 Aims and objectives ......................................................................................................................1

    2 Study on mix design parameters ....................................................................................................3

    2.1 Introduction ............................................................................................................................ 3

    2.2 Mix design considerations ......................................................................................................3

    2.2.1 Bitumen type................................................................................................................... 3

    2.2.2 Foaming conditions.........................................................................................................4

    2.2.3 Foam characteristics .......................................................................................................4

    2.2.4 Aggregate properties ......................................................................................................4

    2.2.5 Mixing..............................................................................................................................5

    2.2.6 Mixing and Compaction water content .......................................................................... 5

    2.2.7 Compaction..................................................................................................................... 6

    2.2.8 Curing ..............................................................................................................................7

    2.2.9 Materials .........................................................................................................................8

    2.3 Methodology.........................................................................................................................10

    2.3.1 Introduction ..................................................................................................................10

    2.4 Results and Discussion..........................................................................................................14

    2.4.1 Optimum foam characteristics......................................................................................14

    2.4.2 Design gradation ...........................................................................................................15

    2.4.3 Optimum mixing water content (pre wet water content)............................................ 18

    2.4.4 Optimum compaction effort ......................................................................................... 20

    2.4.5 Mixture volumetric composition ..................................................................................23

    2.4.6 Selection of Foamed Bitumen content (Mechanical tests)...........................................25

    2.5 Conclusions ...........................................................................................................................28

    3 Study on accelerated curing..........................................................................................................30

    3.1 Scope of the study ................................................................................................................30

    3.2 Effect of time and temperature on water loss .....................................................................30

    3.3 Effect of time and temperature on stiffness.........................................................................31

    3.4 Effect of water content on stiffness...................................................................................... 33

    3.5 Effect of RAP and Cement on stiffness .................................................................................33

    3.6 Conclusions ...........................................................................................................................34

  • 8/21/2019 Mix design of foamed bitumen mixtures

    2/40

    3.7 Further curing study..............................................................................................................34

    4 Further study................................................................................................................................. 35

    4.1 Generating inputs for Pavement analysis and design (June 2013 August 2013)...............35

    4.1.1 Specimen Fabrication.................................................................................................... 35

    4.1.2 MEPDG inputs frequency sweep test.........................................................................35

    4.1.3 Material constants generation for non-linear elastic analysis...................................... 36

    4.2 Analysis and design (September 2013 January 2013)........................................................36

    4.2.1 Non-linear elastic analysis using KENLAYER.................................................................. 36

    4.2.2 Sensitivity analysis of distress types to FBM inputs......................................................36

    4.3 Fatigue and durability study (February 2014-June 2014).....................................................36

    5 References .................................................................................................................................... 37

  • 8/21/2019 Mix design of foamed bitumen mixtures

    3/40

    1

    1 Introduction

    1.1 Problem statement

    Unlike Hot Mix Asphalt (HMA) in which bitumen and aggregate are primary components, in foamed

    bitumen (FB) treated mixtures, water and, often, active fillers are the additional ingredients.

    Therefore, FB mixtures involve more variables, have a less controllable mixing procedure, and are

    expected to exhibit more complex behaviour than HMA. It is a very common practice to add

    cementitious additives in FB treated mixtures (FBM) for various reasons such as; to achieve early

    strength, accelerated curing. Moreover, this technique of bitumen foaming has commonly been

    used for recycling, which means mixtures including Reclaimed Asphalt Pavement (RAP) material.

    From the literature review it was understood that the permanent deformation behaviour of FBM

    with cementitious and RAP addition is well documented (Halles and Thenoux, 2009,Jenkins, 2000).

    However, fatigue behaviour of these mixtures with these additives has not been studied so

    extensively. It is a well-known fact that FB mixtures are neither fully bound (like HMA) nor unboundmixtures. The presence of mastic (fines + bitumen) brings a difference in these mixtures in which

    aggregates are bonded with this mastic. Therefore, water susceptibility of these mixtures is much

    more important than in the case of HMA. Usually, therefore, tests on FBMs are mostly accompanied

    by water susceptibility tests. FBMs gain strength with time after compaction. This is due to loss of

    mixing water in the mix over the time. This process of gaining strength of FBM with expulsion of

    water is called curing. With reduction of water in FBM strength (compressive and tensile) and

    stiffness increase (Asphalt academy, 2009). Maturity functions can potentially be used to convert the

    actual curing temperature to an equivalent temperature. This concept of a time-temperature factor

    can be used to quantify the strength development of FB mixtures.

    It has been learned that stress and strain signals occur in the pavement under traffic loading. The

    magnitude of the stress varies from one location to the other. HMA exhibits stress independent

    behaviour at least to a certain level of stress. So, it has been a common practice to analyse HMA

    layers using linear elastic theory. Due to the un-bound nature of the FB mixtures, applicability of

    linear (stress dependency) behaviour is questionable. In order to obtain reliable stress and strain

    data from analysis, an experimental program with varying stress levels has to be carried out.

    After detailed literature review, the following aim and objectives are considered.

    1.2 Aims and objectivesThe primary aim of this research is to understand the behaviour of FB mixtures with cementitious

    additives and RAP material and to design pavements with FBM layers with some confidence.

    The objectives of the research are as follows;

    1. Detailed literature review of mix design and structural design procedures that are being

    followed by different agencies.

    2. Identifying critical mix design parameters and studying their influence on mechanical

    properties.

    3. Understanding curing (water loss and strength gain) mechanisms in FBM.

    4. Developing strength-maturity relationships for FB mixtures.

  • 8/21/2019 Mix design of foamed bitumen mixtures

    4/40

    2

    5. Studying fatigue behaviour and durability of FB mixtures with cement and RAP material.

    6. Understanding the stress dependency behaviour FB mixtures.

    7. Conducting mechanistic (non-linear elastic) analysis of pavements with FB layers by using

    the results obtained in 4.

    8. Designing pavements (structural design) using the Mechanistic Empirical Design Guide

Search related