Recycled Materials in Embankments

The disposal of solid waste has become a major problem over the past few years in the United States. Millions of tons of non-hazardous solid waste are produced each year, and Texas is one of the largest producers. Recycling and use of these waste materials, especially in highway construction, is increasing nationwide.

Proper use of these recycled materials may lead not only to quality roads at considerable savings, but also to solutions for environmental problems. Highways use large volumes of construction material, so highway agencies are frequent participants in efforts to recycle and reuse waste materials.

One way recycled materials have been used successfully is in highway embankments. The three recycled materials used most often are fly ash (Type A or Class F), tire chips, and wood chips. In the 1970s and 1980s fly ash was popular, but in the last five years tire chips have become more popular in embankment construction. Compared to fly ash, both tire chips and wood chips are a lighter-weight fill.

In Texas, using recycled materials will become more popular only if there is better understanding of the materials' behavior, durability, and chemical stability in various loading and environmental conditions. Also, the availability of these materials in large volumes at a reasonable cost will help determine how successfully the materials are used in embankments.

Objectives

The Center for Innovative Grouting Materials and Technology at The University of Houston conducted study 0-1351, "Recycled Materials in Embankments, Except Glass, for TxDOT, the Texas Commission on Environmental Quality (TCEQ), and the Federal Highway Administration (FHWA) to research the use of recycled materials in highway embankments and develop specifications as needed.

Research tasks included:

• Review case studies of recycled materials used in embankments
• Select recycled materials available in Texas
• Evaluate the physical and chemical properties of the selected recycled materials
• Identify embankment configurations, construction methods, and costs
• Develop recycled material embankment specifications and quality control measures.

Findings

The availability of recycled materials and their locations in Texas have been documented. Large quantities are still not being used effectively, however. This study provides information on using five recycled materials in embankments-tire chips, fly ash, bottom ash, scrubber base, and fluorogypsum.

Researchers performed limited laboratory tests to verify the engineering and leaching properties of random samples of the selected materials obtained from various parts of Texas. All of the recycled materials showed very low levels of contaminant leaching during the Toxicity Characteristics Leachate Procedure (TCLP) and Texas Commission on Environmental Quality (TCEQ) tests, and were characterized as Class 3 non-hazardous waste materials.

The behavior of the materials with simulated Texas soils (20% clay/80% sand) was evaluated. The behavior of recycled materials without soils was also studied. The behavior of the recycled materials is comparable to the behavior of sand with Texas soils. Hence recycled materials could be incorporated into earth embankments effectively.

Three types of embankment configurations have been used with recycled materials:

• Placing the recycled material in the core of the embankment, surrounded by soil
• Mixing the recycled material with soil in a homogeneous mix throughout the embankment
• Alternating layers of recycled materials with layers of soil.

Placing the recycled material in the core of the embankment was the most popular configuration. Research also indicates that the use of recycled material can either increase or decrease the cost of embankment construction, with transportation costs being an important factor.

Through the collection and analysis of this information, researchers developed a specification for the use of recycled materials in embankments.

Implementation

The research team believes future research on using recycled materials in embankments should:

1. Perform field studies to evaluate the success of various embankment configurations using Texas soils and recycled materials. Instrument the embankments to quantify short- and long-term settlement of side slopes and evaluate the leachate quality.
2. Evaluate the long-term risk to the environment from using recycled materials in embankments.
3. Develop a new compaction test to evaluate the densities of long tire chips with and without soils.
4. Develop an assurance program to minimize the effects of the variability of recycled material properties.
5. Establish appropriate safety and health practices for handling recycled materials in embankment construction.

The contents of this summary are reported in detail in The Center for Innovative Grouting Materials and Technology Research Report 0-1351, "Recycled Materials in Embankments, Except Glass," C. Vipulanandan, M. Basheer, and M. W. O'Neill, Preliminary Report Dated - January 1996. This summary does not necessarily reflect the official views of the FHWA, TCEQ, or TxDOT.