Shredded tires as an urban local road drainage layer material
Abdul Rahman, Ganiu
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Roads in many northern climates like Saskatchewan can undergo structural failure caused by frost action and substructure moisture problems. Frost action can be efficiently controlled by eliminating at least one of the following conditions: moisture; freezing temperatures; and frost susceptible soils. However, effective use of shredded tire material could provide an environmentally sustainable solution for waste tires and could relieve pressure on limited quality aggregate resources. The City of Saskatoon has successfully incorporated crushed rock and crushed recycled concrete as a subsurface road drainage layer to mitigate substructure drainage and frost issues. However, the price of crushed high value aggregates can be cost prohibitive and at times these materials are not available in quantities required. Previous research has documented that shredded tires are efficient in controlling frost action by providing thermal insulation and free drainage, but shredded tires performed poorly as a structural support layer with low mechanical stiffness and high compressibility properties. The goal of this research was to provide improved pavement performance with respect to road substructure moisture drainage and frost mitigation. The specific objectives of this research were to: • Quantify the mechanical properties of shredded tires and investigate the mechanical behavior of mixes of shredded tires with and without sand blended into the tire matrix as compared to conventional subbase and base coarse materials; • Determine the permeability of shredded tires and investigate the effect of sand on the permeability of shredded tire/sand mixes as compared to conventional granular base and subbase materials, and; • Compare the structural primary response behavior and capital cost of alternate road structures constructed with shredded tires and mixes of shredded tire and sand as a free draining subbase material compared to conventional drainage layers and road structures. The hypothesis of this research was that the mechanical behavior of shredded tire material, used as a road substructure layer, can be improved by blending it with free draining sand. It was also hypothesized that blending shredded tire with free draining sand will have improved drainage compared to conventional granular subbase and base course materials. Volumetric and mechanistic material properties and structural performance behavior of shredded tires and shredded tire/sand mixes in the mix ratios (by volume) of 1Tire:1Sand, 1Tire:2Sand and 1Tire:3Sand were evaluated and compared to City of Saskatoon subbase materials: crushed rock and granular base; as well as Saskatchewan Ministry of Highways and Infrastructure (SMHI) Type 6 subbase. Laboratory characterization showed that 100% shredded tire materials were uniformly graded indicating high amounts of voids. The addition of sand resulted in a reduction of interparticle air voids. Results from strength and stiffness characterization tests indicated that 100% shredded tires exhibited low structural stiffness, but this behavior was improved as the quantity of sand in the shredded tire was increased. The 100% shredded tire material was determined to have a dynamic modulus value of 5MPa, whereas shredded tires/sand blends at the ratios of 1Tire:1Sand, 1Tire:2Sand and 1Tire:3Sand gave dynamic moduli values of 30MPa, 110 MPa and 158MPa, respectively. For comparison, SMHI Type 6 subbase, City of Saskatoon crushed rock and granular base exhibited dynamic moduli values of 94MPa, 174MPa and 471MPa, respectively. Permeability characterization indicated that the 100% shredded tire materials were free draining at 1.42cm/s. Permeability decreased from 1.42cm/s with 100% shredded tire to 0.0026cm/s with 1Tire:3Sand. However, the shredded tire/sand mixes maintained permeability values higher than sand (0.0013cm/s). SMHI Type 6 subbase and granular materials were found to have a permeability of 0.0018cm/s and 0.000025cm/s, respectively, while crushed rock was free draining with a permeability of 1.12cm/s. Structural behavior of 100% shredded tire, shredded tire/sand mixes and City of Saskatoon subbase materials were studied in road models using a 3-D numerical road modeling software that encoded triaxial material constitutive relationships determined in this research. A typical City of Saskatoon road structure was assumed for all road structures considered in this study with varying subbase material so as to directly compare the structural effect of the shredded tire with conventional road materials under primary load limits. Modeled results of the 100% shredded tire and crushed rock roads showed peak surface deflections of 2.19mm and 0.73mm, respectively. Peak surface deflection under primary load limits was found to decrease with an increase in sand quantity within the shredded tire layer. Based on the modeling results, 1Tire:2Sand and 1Tire:3Sand yielded peak surface deflections of 1.01mm and 0.96mm, respectively. For comparative purposes, road structures with SMHI Type 6 subbase deflected at 1.14mm. Field test sections were constructed at Adolph Way in Saskatoon to compare the structural performance of shredded tire to crushed rock (currently specified by City of Saskatoon for drainage layers) in a typical residential road in Saskatoon. Unfortunately, both crushed rock (control) and shredded tire sections were found to deflect above acceptable limits due to high moisture conditions within the deep subgrade. Therefore, deeper excavation was required and the test sections were not constructed. The Adolph Way field experimentation of shredded tire showed that shredded tire road systems can be effectively constructed in the field, but showed the same sensitivity to poor subgrade conditions as crushed rock. Capital cost analysis showed the 100% shredded tire and shredded tire/sand subbase layers to be less expensive than City of Saskatoon specified crushed rock drainage layers. The 100% shredded tire layer was estimated at a total cost of $2.93/m2 while 1Tire:1Sand, 1Tire:2Sand and 1Tire:3Sand were estimated at $4.39/m2, $4.88/m2 and $5.12/m2, respectively. SMHI Type 6 subbase, crushed rock and granular base layers were estimated at a total cost of $5.85/m2, $13.95/m2 and $9.00/m2, respectively for equivalent thickness. From the structural, permeability and economic perspective of this research, the 1Tire:2Sand and 1Tire:3Sand materials proved to be cost efficient as well as technically viable options for mitigating frost action as compared with City of Saskatoon crushed rock materials evaluated. The use of shredded tire/sand mixes of 1Tire:2Sand and 1Tire:3Sand in urban local road structures with low traffic volumes are therefore recommended as a cost effective subbase drainage layer material.
DegreeMaster of Science (M.Sc.)
DepartmentCivil and Geological Engineering
CommitteePark, Peter; Sparks, Gordon
Copyright DateSeptember 2014