Recycled Materials in Geotechnics

When shredded, tires can be used as a lightweight construction material and a sorptive drainage medium alone or in mixture with soils. When mixed with soils, shredded tires generate a lower unit weight geomaterial often with improved engineering properties compared to those of the soil alone, especially in terms of strength. Furthermore, tire chips display significant sorptive properties, which make them a cost-effective sorptive drainage layer in environmental applications. There has been a significant amount of research in the last decade to characterize the engineering and chemical properties of tire chips and tire chips-soil mixtures in the laboratory as well as investigations of mass behavior in the field. This paper summarizes the behavior of shredded tire-soil mixtures as a lightweight geomaterial and a sorptive drainage medium based on the research carried out at the author's institution and as found in the literature.

The current status on the use of recyclable materials in construction works in Japan, mainly in geotechnical applications, is presented in this paper. Firstly, the generation of waste and by-product materials from construction works is presented. Secondly, a classification for the by-products is made based on the type of treatment and its application. The intermediate treatment techniques for geotechnical utilization are listed along with their applicability to the construction engineering field. Among recyclable materials, the status of surplus soil, waste sludge/slurry, coal fly ash, and MSW (municipal solid waste) incinerator ash is reviewed in this paper. The potential environmental impact during the reuse of these by-products is also discussed. Lastly, the legal system in Japan concerning the use of recyclable materials is presented, including some future perspectives.

There are growing interests in the utilization of recycled tire bales for civil engineering applications, triggered partly by the significant volumes of tires that could be disposed of in transportation projects. However, evaluation of bale properties and performance is, at least, limited. This paper summarizes the benefits and shortcomings of using tire bales in civil engineering projects, as well as information collected to date on their mechanical properties. In addition, a summary of the current U.S. scrap tire market is presented, which is supported with case studies and an economic analysis comparing the cost of tire bales to conventional fills. Finally, recommendations for further research on the behavior of tire bales as a lightweight fill are presented.

The low in-place density of tire derived aggregate (TDA) makes them attractive for use as lightweight fill for embankments constructed on weak ground and backfill for retaining walls. TDA, also know as tire shreds or chips, are scrap tires that have been cut into 50 to 300 mm (2 to 12 in.) pieces. There are many examples of projects that have successfully used TDA as lightweight fill. However, as illustrated by three projects built in 1995 that experienced internal heating reactions, care is needed to properly design and construct TDA fills. The underlying cause of these problems was a combination of oxidation of exposed steel belts and freshly cut surfaces on rubber pieces. The lessons learned from these projects resulted in design guidelines to limit internal heating of TDA fills. Nine projects have now been built in accordance with the guidelines. Internal measurements show that TDA temperatures are similar to background soil levels, indicating the effectiveness of the guidelines. Moreover, effective construction specifications have been developed that often result in lower construction costs than competing lightweight fill materials.

Waste paper sludge, or fiber-clay as it if often identified when used as a resource for recycling and reuse in new applications, has over the last several years become a vital component in several geotechnical uses and a variety of manufactured products. Among the major reuses of fiber-clay has been its use as a cover material for sanitary landfills, after thorough laboratory and field evaluations. Because of the high kaolin clay content in the manufacturing of paper products, there is a high residual of clay in waste paper sludge from the manufacturer's waste water treatment plants. The reuse for cover material has resulted in a cost avoidance for the waste generator, reducing or eliminating disposal costs as well as eliminating the need for finding a disposal site. There are also cost savings for landfill operators and owners who otherwise would have to secure an adequate clay source. When compacted, most fiber-clays exhibit adequate hydraulic conductivity and shear strength for use in landfill covers. In addition to its use as a cover material, the fiber-clay, when combined with a pozzalonic material such as fly ash and aggregate, has been used as one of the major components of road beds, both as subsurface base and as a finished surface for remote access and secondary roads. Additional uses include the manufacturing of kitty litter and animal bedding. This paper will review the history and technology involved in evaluating the potential uses of fiber-clay. Extensive laboratory and field testing has been done to determine its shear strength, slope stability, hydraulic conductivity, and settlement potential. Information is presented on the various testing techniques and results, together with examples of actual field projects.

The process of composting of organic wastes is expanding rapidly in the United States and other countries since landfill spaces for disposal of organic wastes are becoming scarce and expensive. Compost materials, given their moisture affinity and low hydraulic conductivity, can provide stabilization of natural expansive soils by mitigating shrinkage cracking and encapsulating subsoil surfaces. To verify these advantages, a research study was conducted to measure the geotechnical characteristics of composts and compost treated topsoils (CMTs). Two types of composts, Dairy Manure and Biosolids, and a local expansive soil were used as materials. This paper presents laboratory test results from Atterberg, organic content, direct shear strength, free swell, linear shrinkage, and hydraulic conductivity tests and analyses of these results to evaluate the potential applications of CMTs to serve as highway shoulder covers to mitigate shrinkage cracks. The results indicate that shrinkage strains are reduced and strength and swell strains are increased with the use of compost amendments. Environmental assessments including the presence of organic matter are also addressed.

This paper presents a variability study of several engineering properties of recycled rubber tire pieces based on a comprehensive literature survey of experimental test programs. The unit weight, cohesion, internal friction angle, Young's modulus of elasticity and Poisson's ratio were evaluated and compared to engineering property variability of natural soils. In addition, a series of regression and residual analyses were performed to investigate the presence and significance of scale-dependency on the engineering properties of rubber tire pieces. The results of the variability analysis show that unit weight and Poisson's ratio have the lowest values of coefficient of variation whereas the shear strength parameters and the elastic modulus have the highest. From the regression analysis, cohesion and Young's modulus showed the greatest sensitivity to changes in maximum tire particle size. However, these results are based on statistics that have limitations when used for interpretive purposes. A non-statistical investigation based on geotechnical theory was used to further evaluate the scale-dependency of the shear strength parameters. Using Mohr-Coulomb failure theory and assuming that the cohesion component of strength is justifiably neglected, the analysis showed a scale-independent relationship which is consistent with the statistical findings for internal friction angle.

This paper describes a case history where Class C fly ash, an industrial byproduct of electric power production, was used to stabilize a sandy clay highway subgrade so that a firm working platform could be provided for pavement construction. California bearing ratio (CBR), resilient modulus (M_r), and unconfined compressive strength tests were conducted on the soil alone and the soil-fly ash mixture to assess how fly ash improves the bearing resistance, stiffness, and shear strength of the soil. Field tests were also conducted during construction using a soil stiffness gauge (SSG) and a falling weight deflectometer (FWD) to assess the stiffness and modulus of the stabilized soil in situ. CBRs ranging between 46 and 150 were obtained for the stabilized soil after 7 d of curing, whereas the soil typically has CBR near 0 in its naturally moist condition (~5% wet of optimum water content). M_r of the stabilized soil ranged between 11 and 28 MPa after 7 d of curing and between 17 and 68 MPa after 28 d of curing, whereas the unstabilized clay was too soft to determine its M_r using conventional methods. SSG tests indicated that the in situ stiffness of the stabilized soil ranged between 19 and 31 MN/m after 7 d of curing, whereas the unstabilized soil had a stiffness between 8 and 21 MN/m. Moduli computed from the stiffness measurements made with the SSG were in good agreement with those determined from the FWD data, but both were about 10 times higher than those from the M_r tests. Unconfined compressive strengths (q_u) of the stabilized soil ranged between 276 and 607 KPa after 7 d of curing and between 304 and 683 KPa after 28-d of curing, whereas q_u of the unstabilized soil was less than 200 kPa.

Over 7.3-million tons of waste asphalt roofing shingles are generated each year in the US, and beneficial uses are needed to avoid costly disposal in landfills. Construction firms and state. DOTs have investigated blending ground shingles with soils for use in pavement structures. These studies indicated that the addition of shingles had beneficial effects on some soils, however only qualitative observations were made. The objective of this study was to obtain some baseline quantitative data on the physical and mechanical effects that shingles have on soils. We added shingles to a crushed stone gravel, a silty sand, clean sand, and a clay. This work showed that for weak materials like clays, 25.4 mm (1-inch) minus shingles can potentially improve their strength. For inherently strong granular materials like gravels and sands, shingles can potentially diminish their strength from initially high values. However, the results indicate that these materials mixed with shingles can still provide adequate subgrade support for pavements and light structures.

A thorough evaluation of potential beneficial uses of dredged sediments is increasingly important for large dredging projects. This paper presents the results of a field and laboratory testing program to characterize sediments and evaluate beneficial use options for the redevelopment of a former naval base in Rhode Island. A combination of sidescan and subbottom acoustic profiling, gravity coring, and vibracoring provided an efficient and cost-effective alternative to traditional drilling and sampling site investigation techniques. The sediments at this site consisted of organic silts, clayey silts, and silty sands. Building debris from the site was blended with the silty sand to meet common borrow specifications. The clayey silt was stabilized with lime for use as structural fill and hydraulic conductivity tests on compacted specimens of untreated clayey silt were also performed. The results suggest that the clayey silts may be used as a capping material for brownfields remediation or landfills.

In this study, soil-tire shreds was used as a backfill material behind a fully instrumented modular wall. A mechanically stabilized earth wall reinforced with geotextiles and geogrids and backfilled with a sand-tire shred mixture (25% tire shreds by volume) was designed and constructed using conventional geotechnical methods. After construction, the wall was loaded with a surcharge and monitored to assess the mass behavior of soil-tire shred backfills. Successive surcharges were placed corresponding to 42, 95, 148, and 200 kPa. The wall was instrumented with earth pressure cells, position transducers to measure displacement of the wall face, and strain gages to monitor strains in the geosynthetic reinforcement. Horizontal and vertical pressures behind the wall increased as the surcharge was placed, but at different rates depending on depth. Strain in the geotextile and geogrid layers also increased as the surcharge increased, with larger strains occurring near the face of the wall. Displacements of the face of the wall were largest near the top, and increased as the surcharge was placed. However, the displacements generally were small, even under the heavy surcharge. A favorable comparison was also obtained between deformations predicted using a finite element model and those measured in the field. The small displacements that were observed demonstrated that earth structures using soil-tire shreds backfills can be reliably designed and constructed with conventional geotechnical methods.

Due to the scarcity of virgin materials, the reuse of granular materials in the road construction becomes of growing importance. However, the use of such recycled materials should not lead to a decrease in quality of the bearing capacity and the life cycle of the road. The compaction of recycled materials requires existing techniques to be adapted to achieve this requirement. The classic compaction theory of granular soils, when applied to recycled materials, does not satisfy the demands on the quality because of the different grain strengths. The recycling materials require increased compaction energy. The Swiss standard on compaction of soils is actually based on the classical AASHTO standard method, which has been the worldwide leading protocol in this field of research. Several tests measuring the bearing capacity and the compaction characteristics of two typical recycling materials have been carried out at the ETH (Swiss Federal Institute of Technology). An attempt has been made in order to correlate the degree of compaction and the bearing capacity of the recycled materials. The bearing characteristics have been measured following the standardized CBR test; the compaction test has been performed according to the Swiss standards. These tests show an interesting response from the recycled materials, which does not match the known dependence of compaction, density and bearing capacity.

Even though many states have developed beneficial reuse regulations for industrial by-products, large quantities of foundry sands are being landfilled throughout the U.S. Since the major components of foundry sands are sand and bentonite, they are expected to be suitable hydraulic barrier materials. This project identified the key properties that foundry sands should have to be used as barrier layers, and investigated construction methods and durability of foundry sands. Factors affecting hydraulic conductivity of foundry sands were also investigated. The project consisted of a laboratory study, a field study, and a modeling study. Sixteen foundry sands from four Midwestern states and one foundry sand from Georgia were tested during the laboratory study. Three test pads were constructed and instrumented during the field study. The field and laboratory studies showed that foundry sands having liquid limit (LL) > 20 and/or a bentonite content > 6% can be compacted in the field to achieve hydraulic conductivity < 10^–7 cm/sec. Tests were also indicated that foundry sands were resistant to freeze-thaw and wet-dry cycling. A network formulation was used to model the hydraulic conductivity of foundry sands as a function of bentonite content. The sand particles were assumed to be spheres. Pores between the spheres were approximated as a network of straight capillary tubes. Bentonite was modeled as a coating of sand particles. The relationship between hydraulic conductivity and bentonite content obtained from the network model was similar to that measured on foundry sands.

Although there has been a rise in the use of recycled materials in highway and geotechnical systems, many tons of potentially useful industrial and domestic by-products are still being discarded in the United States each year. While extensive research has been conducted to investigate the use of recycled materials in engineering applications, the dissemination of the findings is often limited. The problem is compounded by the lack of a single resource containing relevant engineering and environmental characteristics of each material; the tendency of the researchers to publish their findings in technical reports rather than archived publications; and the wide discrepancies among local and state environmental regulations and acceptability. A relational database is proposed as a method to improve dissemination and implementation of recycled material research. A comprehensive review is conducted on data available for a wide variety of recycled materials and their usage in highway and geotechnical applications. Mechanical and environmental data and information from case histories are organized into approximately 10 tables in a relational database management system (DBMS). More than 30 parameters, including engineering properties, availability and cost, are recorded for 21 materials in a highly-organized compendium. Through a simple user interface, a vast amount of data can be sorted to implement a recycled material program based on historic and current data. The DBMS is updatable and the design is amendable to account for future expansion.

Sustainability in the construction industry can only be achieved through a radical rethinking of building construction and reuse. This paper outlines the problems and offers innovative solutions that embrace technological innovations, advances in manufacturing and distribution, and integration of building and land use concepts through: 1) application of a dismountable and reconfigurable structural system, 2) promotion of the concept of kitting, and 3) reconceptualization of the relationships between construction management, engineering, supply chain configurations, environmental modeling, design, and urban planning. Basic components are described with the modeling and research agenda needed to make these solutions both viable and adoptable.