abstract title of document: investigating crumb rubber

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  • ABSTRACT

    Title of Document: INVESTIGATING CRUMB RUBBER

    AMENDMENTS FOR EXTENSIVE GREEN ROOF SUBSTRATES

    Sonia Lorelly Solano Torres, MS, 2010

    Directed By: John D. Lea-Cox, PhD. Chair, Plant Sciences

    and Landscape Architecture Department

    Extensive green roof systems can mitigate urban stormwater by capturing rainfall and

    reducing runoff volume. Green roof substrates, often made from expanded shales,

    slates and clays are fundamental for roof hydraulic dynamics, and for providing

    optimal plant growth conditions. However, these substrates occasionally impose load

    limitations for retrofitting existing infrastructure. This research studied recycled-tire

    crumb rubber, as a light-weight material for amending green roof substrates. Zinc

    release from crumb rubber was quantified, and the interactions with commercial

    rooflite substrate and the effect of high Zn concentrations on the growth and uptake

    by Sedum were studied. Zn was found to leach from crumb rubber in quantities that

    could negatively affect plant growth; however, Zn was adsorbed onto cation exchange

    sites of the mineral and/or organic portion of rooflite, preventing negative growth

    effects in Sedum. Crumb rubber could be utilized as an amendment with substrates

    having high cation exchange capacities.

  • INVESTIGATING CRUMB RUBBER AMENDMENTS FOR EXTENSIVE GREEN ROOF SUBSTRATES.

    By

    Sonia Lorelly Solano Torres.

    Thesis submitted to the Faculty of the Graduate School of the University of Maryland, College Park, in partial fulfillment

    of the requirements for the degree of

    Masters in Science 2010

    Advisory Committee: John D. Lea-Cox. PhD., Chair Andrew G. Ristvey. PhD., Co-Chair Steven Cohan. PhD.

  • Copyright by Sonia Lorelly Solano Torres

    2010

  • ii

    Dedication

    This thesis is dedicated to my parents, who have always trusted and supported my

    abilities to reach my goals.

  • iii

    Acknowledgements

    I would like to express my sincere appreciation to all my committee members

    for the opportunity of working and learning from them. I owe my deepest gratitude

    to Dr. Andrew Ristvey, who always supported my research and assisted my

    understanding of this topic.

    I would also like to thank Mr. Edmund Snodgrass for giving

    me inspiration with his great passion for green roofs. His unassuming character and

    wealth of knowledge are an example for all green roofers.

    I extend my gratefulness to Professors Carlos Mendez, Juan Ramon Navarro

    and Luis Felipe Arauz from the University of Costa Rica, for all the guidance and

    motivation I received from them during the early years of my career.

    I appreciate the financial support of Maryland Environmental Service and the

    Department of Plant Science and Landscape Architecture at the University of

    Maryland.

    Finally, I would like to acknowledge the immense kindness I found in this

    country. Thanks to my friends and colleagues who made me feel welcome during

    these years.

  • iv

    Table of Contents Dedication ..................................................................................................................... ii Acknowledgements ...................................................................................................... iii Table of Contents ......................................................................................................... iv List of Tables ............................................................................................................. viii List of Figures .............................................................................................................. ix Chapter 1: Literature Review ........................................................................................ 1

    A. The Urban Context: Stormwater Runoff .............................................................. 1 B. Green Roofs .......................................................................................................... 6

    B.1. Historical Background and Definition ......................................................... 6 B.2. Green Roof Systems Classification .............................................................. 8 B.3. Intent and Benefits of Extensive Green Roof Systems .............................. 10 B.3.1. Environmental Benefits ............................................................................ 11 B.3.1.1. Stormwater Management and Water Quality Improvement ................. 11 B.3.1.2. Habitat Creation ................................................................................... 14 B.3.1.3. Potential Reduction of the Urban Heat Island ...................................... 15 B.3.2. Economic Benefits ................................................................................... 15 B.3.2.1 Increased Roof Life ................................................................................ 16 B.3.2.2. Cooling, Insulation and Energy Efficiency .......................................... 16 B.3.2.3. Green Building Assessment and Public Relations ............................... 17 B.3.3. Aesthetic Benefits .................................................................................... 17 B.4. Extensive Green Roof System Components and Construction ................... 18

  • v

    B.4.1. The Deck .................................................................................................. 18 B.4.2. Waterproofing Layer ................................................................................ 18 B.4.3. Insulation Layer ........................................................................................ 19 B.4.4. Root Barrier .............................................................................................. 19 B.4.5. Drainage Layer ......................................................................................... 20 B.4.6. Root Permeable Filter Layer .................................................................... 21 B.4.7. Substrate Layer ......................................................................................... 21 B.4.8. Vegetation Layer ...................................................................................... 27 B.4.8.1. Succulent Plants ................................................................................... 28 B.4.8.2. Native Plants and Short Grass Prairie Species ..................................... 29

    C. Investigating Crumb Rubber as a Potential Amendment for Extensive Green Roof Substrates ....................................................................................................... 30

    C.1. Crumb Rubber and Zinc .............................................................................. 30

    D. Objectives of this Research ............................................................................... 37

    Chapter 2: Substrate Based Studies ............................................................................ 38

    A. Introduction ........................................................................................................ 38 B. Methodology ...................................................................................................... 41

    B.1. Experiment 1: Quantification of Zn release over time from crumb rubber exposed to acidified and non-acidified reverse-osmosis water solutions ........... 41 B.2. Experiment 2: Adsorption of Zn in crumb rubber amended green roof substrates ............................................................................................................. 42 B.3. Experiment 3: Quantifying available Zn leachates from green roof substrates, with and without crumb rubber ......................................................... 44

    C. Results ................................................................................................................ 48

    C.1. Experiment 1: Quantification of Zn release over time from crumb rubber exposed to acidified and non-acidified RO water solutions ............................... 48

  • vi

    C.2. Experiment 2: Adsorption of Zn in crumb rubber amended green roof substrates ............................................................................................................. 50 C.3. Experiment 3: Quantifying available Zn from leachates of substrates, with and without crumb rubber ................................................................................... 53

    D. Discussion .......................................................................................................... 56

    D.1. Experiment 1: Quantification of Zn release over time from crumb rubber exposed to acidified and non-acidified RO water solutions ............................... 56 D.2. Experiment 2: Adsorption of Zn in crumb rubber amended green roof substrates ............................................................................................................. 57 D.3. Experiment 3: Quantifying available Zn from leachates of substrates, with and without crumb rubber ................................................................................... 58

    Chapter 3: Plant Substrate Interactions .................................................................... 60

    A. Introduction ........................................................................................................ 60 B. Methods and Materials ...................................................................................... 63

    B

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