MPC
Research Projects (2008-09)

Identifying Number

MPC-303

Project Title

Seed Project: Beneficial Use of Off-Specification Coal Combustion Products to Increase the Stiffness of Expansive Soil-Rubber Mixtures, Year 1

University

Colorado State University

Project Investigator

Dr. J. Antonio H. Carraro, Assistant Professor
Department of Civil and Environmental Engineering
Phone: (970)491-4660, E-mail: carraro@colostate.edu

Description of Project Abstract

Untreated native soil with high swell potential has been identified by the Colorado Department of Transportation as one of the major contributing factors in the development of premature longitudinal cracking and other pavement distresses in Colorado (Ardani et al. 2003). Although excessive movement of pavement and bridge structures has been reported in both rural and urban areas in Colorado, this issue represents a particular burden for local governments due to the excessive costs associated with the construction, management and operation of low-volume roads and bridges founded on expansive soils. An ongoing study led by the PI that is also sponsored by the USDOT-MPC is investigating whether expansive soil-rubber (ESR) mixtures may be used as an alternative, sustainable material in low-volume road and bridge construction. That study has an innovative character because (i) most of the previous studies involving the use of rubber to stabilize soils have dealt with rubber-sand mixtures (Lee et al. 1999; Yoon et al. 2006; Zornberg et al. 2004), and (ii) among the few previous studies that have focused on rubber-clay mixtures (Ahmed and Lovell 1993; Edil and Bosscher 1994; Tatlisoz et al. 1997), none of them had investigated the effect of rubber on the engineering properties of highly-expansive clays such as the ones found in rural and urban areas in Colorado. One of the major findings of the ongoing study mentioned previously is that scrap tire rubber addition decreases both the swell pressure and the swell percent of expansive soils (Carraro et al. 2008; Seda et al. 2007). However, a reduction in stiffness is also observed in ESR mixtures due to the deformability of the rubber particles and their effect on the structure of the compacted ESR mixtures (Carraro et al. 2008). Thus, methods that allow improvement of the stiffness properties of ESR mixtures should be investigated.

In the research proposed herein, the beneficial use of off-specification (OS) coal combustion products (CCPs) is evaluated through a systematic experimental investigation. Due to more recent environmental regulations, widely-used CCPs such as fly ash (FA) have been commingled with additional materials that are used to minimize the environmental impacts due to emissions from coal combustion power plants. As a result, some of today’s FA may not meet conventional specifications. This has compromised the wide spread use of FA and other CCPs in civil engineering applications. Thus, this study will focus on whether or not OS-FA materials may be used to improve the stiffness of ESR mixtures. The mechanical response of expansive soil rubber (ESR) mixtures stabilized with OS-FA will be investigated through a comprehensive experimental program. It is expected that the pozzolanic characteristics of OS-FA will be sufficient to improve the stiffness of the ESR mixtures so that these alternative, sustainable materials can be used in low-volume road and bridge construction.

roject Objective

The main objectives of this project are: (i) to evaluate the geotechnical properties of expansive soil-rubber (ESR) mixtures stabilized with OS-FA required for the mechanistic design of low-volume road embankments and bridge abutments, and (ii) to disseminate the project findings through the publication and presentation of a technical paper.

Project Approach/Methods

This study will evaluate the beneficial use of OS-FA on the stabilization of ESR mixtures by measuring the relevant mechanical properties of OS-FA-ESR mixtures through a systematic experimental investigation. It is anticipated that the American Coal Ash Association (ACAA) and its member institutions will help provide the materials that will be used in this feasibility study. Project tasks include:

• Task 1 - Literature review: comprehensive review of the literature on the project’s topic; compilation of a source availability map for all CCP suppliers in Colorado and their proximity to major expansive soil deposits.
• Task 2 – Laboratory testing: sample collection, physical characterization (grain-size distribution, specific gravity, plastic and liquid limits) of the materials tested; mixture design and determination of the standard (ASTM D698) and modified (ASTM D1557) compaction parameters, swell percent and pressure; and triaxial testing (at effective confining stress levels typically encountered in road embankments and bridge abutments) to determine the small- and large-strain stiffness parameters of the ESR mixtures stabilized with OS-FA.
• Task 3 – Report writing: write up of the final USDOT/MPC technical report and technical paper.
• Task 4 – Technology transfer: a technical paper will be prepared and presented at the 2009 Summer Workshop of the Transportation Research Board’s ADC60 - Committee for Waste Management and Resource Efficiency in Transportation.

MPC Critical Issues Addressed by the Research

All critical issues listed below are related to the USDOT Strategic Goal “Infrastructure Management and Environmental Stewardship”: (a) Critical Issue #15: Improved Infrastructure Design (refine pavement damage estimates based on the new damage models presented in the mechanistic design guide; estimate inputs and identify prototype procedures that can be used by state transportation departments in the region; and quantify the effects of traffic and environmental factors on alternative designs); (b) Critical Issue #16: Infrastructure Longevity (developing and applying advanced technologies and innovative materials); and (c) Critical Issue # 17: Environmental Impacts of the Infrastructure (use of recycled materials).

Contributions/Potential Applications of Research

Possible applications of the proposed technology include the use of OS-FA-ESR mixtures as embankment, bridge abutment or backfill material in low-volume road and bridge construction in areas where expansive soils abound. With minor modifications, the technology may be adapted to other applications such as design of residential foundations or construction of trail surfaces in federal and state parks.

Technology Transfer Benefits

The research products will comprise (1) mentoring of a qualified graduate student and (2) publication and presentation of a peer-reviewed paper. The project will allow the PI to start a close collaboration with local CCP suppliers and ACAA. Additionally, significant environmental benefits will result from large-scale recycling of waste tires and CCPs and their diversion from landfills. All these issues will be disseminated to a national audience at the 2009 TRB-ADC60 Committee Summer Workshop at the end of the project.

Time Duration

July 1, 2008 to June 30, 2009

Total Project Cost

$24,043

MPC Funds Requested

$11,218

TRB Keywords

Low-volume roads, mechanistic design, sustainability, stiffness, resilient modulus

References

1. Ahmed, I.; C.W. Lovell (1993) “Rubber soils as lightweight geomaterials.” Transportation Research Record 1422, TRB, National Research Council, pp. 61-70.
2. Ardani, A; S. Hussain; R. LaForce (2003) “Evaluation of Premature PCC Pavement Longitudinal Cracking in Colorado” Proc. 2003 Mid-Continent Transp. Res. Symp., Ames, IA.
3. Edil, T.B.; P. J. Bosscher (1994) “Engineering properties of tire chips and soil mixtures.” Geotechnical Testing Journal, ASTM, 17 (4), pp 453-464.
4. Lee, J.H.; R. Salgado; A. Bernal; C.W.Lovell (1999) “Shredded Tires and Rubber Sand as Lightweight Backfill” Journal of Geotech. and Geoenv. Eng., ASCE, 125 (2), pp 132-141.
5. Seda, J. H.; Lee, J. C.; Carraro, J. A. H. (2007) “Beneficial Use of Waste Tire Rubber for Swelling Potential Mitigation in Expansive Soils”, Geotechnical Special Publication 172, ASCE, Denver.
6. Tatlisoz, N.; C.H. Benson; T. B. Edil (1997) “Effect of fines on mechanical properties of soil-tire chip mixtures.” ASTM STP 1275, pp. 93-108.
7. Yoon, S; M. Prezzi; N. Z. Siddiki; B. Kim (2006) “Construction of a test embankment using a sand-tire shred mixture as fill material” Waste Management, Elsevier, 26, pp 1033-1044.
8. Zornberg, J. G.; Y. D. Costa; B. Volenweider (2004) “Performance of prototype embankment built with tire shreds and nongranular soil” Transportation Research Record 1874, TRB, National Research Council, pp 70-77.
9. Carraro, J.A.H., Dunham-Friel, J.S., Smidt, M.S. (2008) “Beneficial Use of Waste Tire Rubber for Swell Potential Mitigation in Expansive Soils.” USDOT-MPC Interim Report, Fort Collins, CO.