MPC
Research Projects (2007-08)

Identifying Number

MPC-274

Project Title

Beneficial Use of Waste Tire Rubber in Low-Volume Road and Bridge Construction, Year 2

University

Colorado State University

Project Investigator

Dr. J. Antonio Carraro

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). Unique regional factors such as a semi-arid climate and widely-occurring expansive soil deposits have made cost-effective maintenance and rehabilitation of bridges and pavements a challenging task in the region. 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. Increasing costs of conventional (e.g. gravel, sand) and alternative (e.g. fly ash) road construction materials and heavier truck and farm equipment loads have only added up to the problem.

While waste tire rubber products have been used in many engineering applications such as highway embankments and retaining wall backfills, most of these previous works have dealt with rubber-sand mixtures (Lee et al. 1999; Yoon et al. 2006; Zornberg et al. 2004). Among the few studies that have focused on rubber-clay mixtures (e.g. Ahmed and Lovell, 1993; Edil and Bosscher, 1994; Tatlisoz et al. 1997), none of them have 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.

In this study, the mechanical response of expansive soil rubber (ESR) mixtures and the beneficial use of waste tire rubber on the swell potential mitigation of local expansive soils are evaluated through a systematic and comprehensive experimental investigation. The adequacy of ESR mixtures as an alternative road construction material is evaluated through computational modeling of sections of highway embankments designed with these mixtures. A test section is being constructed in Loveland, CO with the assistance of the Department of Public Works from the City of Loveland. It is expected that the lower swell potential of engineered ESR materials tested in this study (Seda et al. 2007) will help reduce the long term maintenance and rehabilitation costs of local, low-volume roads such as the one that will be constructed during this project.

Project Objective

The main objectives of this project are: (i) to evaluate the geotechnical properties of expansive soil-rubber (ESR) mixtures required for the mechanistic design of low-volume road embankments and bridge abutments, (ii) to design a typical low-volume road embankment cross-section using a mechanistically-based pavement design computer model, (iii) to construct a test section to demonstrate the feasibility of the proposed technology, and (iv) to disseminate the project findings through the publication of technical papers and by giving a presentation to state, county, and city engineers as well as students and professionals interested in the technology.

Project Approach/Methods

This ongoing study addresses the beneficial use of waste tire rubber on the swell potential mitigation of local expansive soils and evaluates the relevant mechanical properties of ESR mixtures through a systematic experimental investigation followed by computational modeling of sections of highway embankments constructed with ESR mixtures. The Department of Public Works from the City of Loveland, one of the project partners, is providing logistic and technical support with the construction of a test section that includes an ESR base layer. A presentation will be given to disseminate the findings among state, county and city engineers involved with the design and management of pavements. Completed and ongoing work tasks for the first year (2006-2007) have included:

• Task 1 – Literature review: comprehensive review of the literature on the project's topic; compilation of a source availability map for all waste tire rubber 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, unconfined compressive and tensile strengths of ESR mixtures; consolidation and triaxial testing (at effective confining stress levels typically encountered in road embankments) to determine the consolidation, shear strength, and small-strain stiffness parameters of the ESR mixtures.
• Task 3 – Mechanistic pavement design: a mechanistically-based pavement design computer program is being used to design typical cross-sections of low-volume road pavements based on the mechanical properties and parameters determined in task 2. ESR pavement sections that (i) present reasonable engineering properties and adequate mechanical response (i.e., tolerable compression strain in the sub-grade, tolerable tensile strain in the surface layer, and acceptable swell percent), and (ii) maximize the beneficial use of waste tire rubber are being considered for the construction of the test section.
• Task 4 – Test section construction: a test section containing a mechanistically-designed ESR base is being constructed with the support of the Department of Public Works of the City of Loveland and supplementary financial assistance provided by the Colorado Waste Tire Program, which is administered by the Colorado Department of Local Affairs (CDOLA).

The planned tasks for the second year of the project (2007-2008) include:

• Task 5 – Construction guidelines: based on the experience accumulated during the construction of the experimental test section, a set of construction guidelines will be developed to help plan and direct future construction of ESR mixtures in the field.
• Task 6 – Cost-benefit analysis: to evaluate the economic and environmental adequacy of the proposed technology. Relevant factors that will help assess both economic and environmental benefits imparted by the proposed technology include determination of: (i) amount of waste tire rubber recycled per unit volume of pavement, (ii) costs associated with the landfill space freed due to the adoption of the proposed technology, and (iii) construction and maintenance costs for the test section.
• Task 7 – Report writing: write up of the comprehensive final USDOT/MPC technical report.
• Task 8 – Technology transfer: a technical presentation will be given to disseminate the findings among state, county and city engineers, and other local geotechnical and transportation engineering professionals and students interested in the proposed technology.

Contributions/Potential Applications of Research

Possible applications for the proposed technology include the use of ESR mixtures as embankment, bridge abutment or backfill material in low-volume road 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 Activities

The research products will comprise (1) mentoring of a qualified graduate student and (2) publication of a MS thesis and peer-reviewed journal paper(s). The construction of a test section is allowing close collaboration with local county and city engineers and the establishment of a solid partnership with the Department of Public Works from the City of Loveland. Additionally, significant environmental benefits will result from large-scale recycling of waste tires and their diversion from landfills. An MPC technical report will be written and results of the project will be presented via teleconference on the Transportation Learning Network.

Time Duration

July 1, 2007 - June 30, 2008

Yearly and Total Project Cost

$75,631 Total $160,577

TRB Keywords

Tire-derived aggregate (TDA), recycling, expansive soil, expansive soil rubber (ESR) mixture, local roads