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Use of Recycled and By-Product Material in Soil-Structures


Recycled and industrial by-product materials are increasingly being used as a cost-reduction road construction material. NCHRP Synthesis 435 on Recycled Materials and Byproducts in Highway Applications summarizes how recycled materials such as glass cullet (GC), recycled asphalt pavements (RAP), recycled concrete aggregates (RCA), scrap tires and industry byproducts are being used in road construction applications such as backfill (NCHRP, 2013).

High end naturally derived aggregate is a desirable and relatively expensive road construction material. High end material is typically required as backfill in soil-structure applications such as retaining walls, culverts, and buried bridges. In some regions, high end naturally derived materials are limited and expensive. Recycled and by-product materials are a potential cost effective alternative to naturally derived aggregates as recycled and by-product materials reduce virgin resourcing and processing, waste disposal, and transportation costs. Utilizing recycled and by-product material redirects material from landfills and conserves natural resources. Additionally, recycled and by-product materials may have preferred material characteristics such as lighter density which could improve performance and lower life cycle cost. However, potential negative impacts such as air and water contamination and variable engineering properties need to be carefully evaluated (NCHRP, 2013, p. 74).

A major barrier to use of recycled and by-product material in soil-structures is limited knowledge. Owners and road practitioners face the challenge of determining whether a recycled and byproduct material can be used and if so, how to select, test, design and install those materials in soil-structure applications successfully. Guidelines for the use of recycled and by-product materials in soil-structure applications need to be developed.


The primary objective is to develop a guideline for use of recycled and by-product fill in soil-structure applications and promote the use of these materials. The guideline would provide engineering properties for various recycled and by-product materials and quantify the environmental, social, and economic co-benefits these materials provide.


Many regions have large stockpiles of waste materials such as recycled asphalt pavement, No. 10 tertiary stone screenings, and recycled concrete. The appeal of recycled and by-product materials has become strong over the years due to economic benefits of using readily available material. Waste material stockpiles are growing as transportation agencies undertaking more maintenance and significantly reducing new road construction. Waste material stockpiles offer owners a potentially viable and economical backfill source for high value soil-structure applications. The economic advantage of using waste materials for regions short on high end naturally sourced materials is of especial value.

Some recycled materials such as RAP are being used in road construction but despite this, RAP stockpiles continue to grow (Hoppe, Lane, Fitch, & Shetty, 2015). Additional high end fill applications are needed. Not completing this research results in agencies furthering their waste material stockpiles resulting in environmental stockpile problems, using valuable materials in lower value applications, and spending additional funds on higher end naturally sourced materials. For reference, an investigation on using recycled materials in highway pavements indicated recycled materials reduce energy consumption (16%), water consumption (11%), and hazardous waste generation (11%) while extending the service life of pavement and offering subbase life-cycle savings of 21% (Lee, Edil, Tinjum, & Benson, 2010).

TRB’s 2013 report on critical issues in transportation (Transportation Research Board, 2013) indicates ‘the impacts on energy, climate, and the environment are unsustainable’. Funding this research offers owners a means to use waste material in an application which has the potential to reduce agency costs and conserve natural resources. Potential soil-structure applications include structural fill for culverts, buried bridges, utilities, pipelines, road base, and MSE walls.

Related Research:

Characterization of Recycled Materials for Sustainable Construction (Edil, 2013)

Presented rapid material characterization for commonly used recycled materials.

NCHRP Synthesis 435: Recycled Materials and Byproducts in Highway Applications (NCHRP, 2013)

A summary of the experiences of transportation agencies in determining the relevant properties for recycled materials and industrial byproducts. Materials used as fill and bases are identified.

Developing Improved Opportunities for the Recycling and Reuse of Materials in Road, Bridge, and Construction Projects(Ellis, Agdas, & Frost, 2014)

A summary of a literature search, laboratory testing and strategies to increase the use of recycled materials in construction. No discussion on soil-structure interaction or applications.

Evaluation of Crushed Concrete and Recycled Asphalt Pavement as Backfill for Mechanically Stabilized Earth Walls, (Rathje, et al., 2006)

RCA is recommended for use in MSE walls but additional screening is required. RAP is not recommended to due creep and corrosion concerns.

Feasibility of Reclaimed Asphalt Pavement (RAP) Use As Road Base and Subbase Material* *(Hoppe, Lane, Fitch, & Shetty, 2015).

A literature study focused on potential alternative uses of RAP. RAP is identified as a viable material for base and subbase layers. No specific discussion on soil-structure applications was provided.

Strength and Creep Characteristics of Reclaimed Asphalt Pavement-Sand Blend Backfill in Mechanically Stabilized Earth Walls (Bleakley, Cosentino , Kalajian, & Patel, 2014)

Strength and performance characteristics are investigated and compared for 100% sand, 100% RAP and sand-RAP blends in MSE walls.

Material Recycling and Reuse – Finding Opportunities in Colorado Highways (Stevens, 2007)

Identifies opportunities to use recycled material. Limited soil-structure information provided. However, soil-structure opportunities identified include RAP and cullet glass as culvert backfill. Cited a demonstration project with cullet glass culvert bedding.

Foamed glass - an alternative lightweight and insulating material (Aabøe and Øiseth, 2004)

The paper investigates the use of granulated foamed glass, produced by recycled waste glass, as a lightweight material for road construction applications.

The paper presents results from the monitoring program on six road projects in which the granulated foamed glass was used. In addition, it gives results from performed laboratory tests and recommendations regarding design criteria and construction procedures related to this lightweight material. Limited information is provided on soil-structure interaction.

Engineering and environmental properties of foamed recycled glass as a lightweight engineering material (Arulrajah et al., 2015)

The paper assesses the engineering properties of foamed recycled glass through a laboratory evaluation and ascertains this novel recycled material as a suitable lightweight fill material in civil engineering applications. Soil-structure interaction is not discussed.

Much of the literature provides general material characterization and potential uses for recycled material. Some studies provide information on the potential performance of some RAP and RCA in MSE walls and foamed recycled glass (FRG) in road construction applications. However, minimal information on use of recycled materials outside of RAP, RCA and FRG is provided for buried structures and no information was provided on by-product materials in culvert and buried bridge applications.

The existing body of knowledge does not appear to address recycled and by-product material field installation testing procedures. This research need statement would address existing knowledge gaps by developing knowledge relevant to buried structures and the general installation of recycled and by-product fill.

Works Cited:

Aabøe, R., and Øiseth, E. (2004). Foamed glass – An alternative lightweight and insulating material. Proc. Int. Conf. "Sustainable Water Management and Recycling", M. Limbachiya, J. Roberts, eds. Thomas Telford Publishing, London, UK, 167-176.

Arulrajah, A., Disfani, M. M., Maghoolpilehrood, F., Horpibulsuk, S., Udonchai, A., Monzur Imteaz, M., and Du, Y.-J. (2015). Engineering and environmental properties of foamed recycled glass as a lightweight engineering material. Journal of Cleaner Production, 94, 369-375.

Bleakley, A. M., Cosentino , P. J., Kalajian, E. H., & Patel, M. J. (2014). Strength and Creep Characteristics of Reclaimed Asphalt Pavement-Sand Blend Backfill in Mechanically Stabilized Earth Walls. Journal of the Transportation Research ZBoard, No. 2462, 18-27.

Edil, T. (2013). Characterization of Recycled Materials for Sustainable Construction. 18th International Conference on Soil Mechanics and Geotechnical Engineering (p. 4). Paris, France: University of Wisconsin-Madison.

Ellis, R., Agdas, D., & Frost, K. (2014). Developing Improved Opportunities for the Recycling and Reuse of Materials in Road, Bridge and Construction Projects. Gainesville, FL: University of Florida.

Hoppe, E. J., Lane, D. S., Fitch, G. M., & Shetty, S. (2015). Feasibility of Reclaimed Asphalt Pavement (RAP) Use As Road Base and Subbase Material. Charlottesville, VA: Virginia Center for Transporation Innovation and Research.

Lee, J. C., Edil, T. B., Tinjum, J. M., & Benson, C. H. (2010). Quantitative Assessment of Environmental and Economic Benefits of Recycled Materials in Highway Construction. Transportation Research Record: Journal of the Transportation Research Board. Volume 2158/2010 Environmental 2010, 138-142.

NCHRP. (2013). NCHRP Synthesis 435: Recycled Materials and Byproducts in Highway Applications, Volume 1. Washington, DC: Transportation Research Board.

Rathje, E., Rauch, A. F., Trejo, D., Folliard, K. J., Viyanant, C., Esfellar, M., et al. (2006). Evaluation of Crushed Concrete and Recycled Asphalt Pavement as Backfill for Mechanically Stabilized Earth Walls. Report No. FHWA/TX-06/0-47177-3. Austin, TX: Centre for Transportation Research, The University of Texas at Austin.

Rathje, E., Trejo, D., & Folliard, K. (2006). Potential Use of Crushed Concrete and Recycled Asphalt Pavement as Backfill for Mechanically Stabilized Earth Walls. Austin, TX: The University of Texas at Austin.

Stevens, M. (2007). Materials Recycling and Reuse - Finding Opportunities in Colorado Highways. Denver, CO: Colorado Department of Trasportation Research Branch.

Transportation Research Board. (2013). Critical Issues in Transportation. Washington, D.C.: Transporation Research Board.


Guidelines for the following stages need to be developed for each material.

· Material selection (including the amount and quality of naturally derived aggregate, if required);

· Required material characteristics (e.g. durability, creep, strength, dimensional stability);

· Lab and field testing requirements;

· Environmental suitability characteristics (e.g. off gassing potential, health and safety hazards);

· List of recycled materials offering high potential to satisfy criteria;

· AASHTO LRFD Bridge Design Specifications properties relevant for soil-structure interaction (e.g. density and moisture content, strength, stiffness, drainage, classification, gradation);

· Installation guidelines;

· Defining environmental, social and economic co-benefits for each recycled material.


Field test installations monitored for a multi-year period would improve design information, field controls and user confidence. Field testing is likely to involve monitoring of the material testing, installation, and post construction state in addition to comparing results to original design predictions.

A small portion of recycled materials and industrial by-products identified in NCHRP Synthesis 435 have been tried in fill or road base applications (Table 35, Volume 1). Research on additional industrial byproducts and alternative waste materials may be beneficial as those materials become a viable potential construction material.


This research is relevant for owners looking for: • Economical alternatives to high end naturally sourced aggregate; • Opportunities to utilize stockpiled waste materials such as recycled asphalt pavement and No. 10 tertiary stone screenings.

Sponsoring Committee:AFS40, Subsurface Soil-Structure Interaction
Research Period:12 - 24 months
Research Priority:High
RNS Developer:Antonio Miglio, Ph.D., P.Eng., M.ASCE, Hydraulic and Pipeline Consultant Engineer; John Schuler, PE, VDOT Materials Division; Kevin Williams, MEB, P.Eng, Atlantic Industries Limited
Source Info:See Table 1 and Works Cited at end of document.
Date Posted:07/13/2015
Date Modified:07/20/2015
Index Terms:Recycled materials, Soil structure, Backfilling, Tires, Concrete aggregates, Building materials, Cost effectiveness,
Cosponsoring Committees:AFF70, Culverts and Hydraulic Structures; ADD40, Transportation and Sustainability
Bridges and other structures

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