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Geoenvironmental behavior of foundry sand amended mixtures for highway subbases

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Geoenvironmental behavior of foundry sand amended mixtures for highway subbasesIntroductionMaterialsTest proceduresGeomechanical testsHydraulic testsClimatic testsEnvironmental testsMicroscopy analysisResults and discussionInfluence of crushed rock content and molding water contentInfluence of compactive effort, curing period, and binder additionInfluence of winter conditionsEnvironmental suitabilitySubbase thickness designConclusionsAcknowledgementsReferencesGeoenvironmental behavior of foundry sand amended mixturesfor highway subbasesYucel Guneya, Ahmet H. Aydilekb,*, M. Melih DemirkanbaDepartment of Civil Engineering, 2 Eylul Campus, Anadolu University, Eskisehir 26480, TurkeybDepartment of Civil and Environmental Engineering, University of Maryland, 1163 Glenn Martin Hall, College Park, MD 20742, USAAccepted 16 June 2005Available online 18 August 2005AbstractThe high cost of landfilling and the potential uses of waste foundry sands have prompted research into their beneficial reuse.Roadways have a high potential for large volume usage of the foundry sands. A laboratory testing program was conducted onsoil-foundry sand mixtures amended with cement and lime to assess their applicability as highway subbase materials. The mixtureswere compacted in the laboratory at a variety of moisture contents and compactive efforts and subjected to unconfined compression,California bearing ratio, and hydraulic conductivity tests. The environmental suitability of the prepared mixtures was evaluated byanalyzing the effluent collected during hydraulic conductivity tests. Finally, required subbase thicknesses were calculated using thelaboratory-based strength parameters. The results of the study show that the strength of a mixture is highly dependent on the curingperiod, compactive energy, lime or cement presence, and water content at compaction. The resistance of foundry sand-based spec-imens to winter conditions is generally better than that of a typical subbase reference material. Laboratory leaching tests indicatedthat if these mixtures later come in contact with water that has been discharged directly to the environment (e.g., drainage throughasphalt pavement), the quality of water will not be affected.Ó 2005 Elsevier Ltd. All rights reserved.1. IntroductionFoundry system sand, whi ch is occasionally referredto as foundry sand, is widely used in the metal castingindustry to create the mold into which molten metal ispoured. The system sand is a blend of silica sand, organ-ic additives, and bentonite as a binder. The properties ofthe foundry sand are determined by the relative amountsof binder and other additives, and are unique to eachmetal casting process. The continued addition of thesebinders and additives creates an excess volume that can-not be stored in the finite storage volume of the foundrysand system. The excess volume is typically landfilledeven though it may have good engineering properties.For instance, the annual generation of foundry systemsand is approximately 9 million and 12 million metrictons in Europe and the United States, respectively,and most of this sand is disposed in waste containmentfacilities (Abichou et al., 2004). At present, only 32% offoundry sand is beneficial ly reused in construction. Thisis mainly due to lack of information on its possible ben-eficial uses or due to regulatory requirements today inforce across some cou ntries that classify foundry sandsamong hazardous wastes (FEAD, 2001; SEPA, 2002).Unless alternative uses of this excess sand are intro-duced, an increase in landfilling costs is inevitable underpresent circumstances.Significant efforts have been made in recent years touse foundry sand in civil engineering construction. Someof the application areas included highway bases andretaining structures (Kirk, 1998; Mast and Fox, 1998;0956-053X/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved.doi:10.1016/j.wasman.2005.06.007*Corresponding author. Tel.: +1 301 314 2692; fax: +1 301 4052585.E-mail addresses: [email protected] (Y. Guney), [email protected] (A.H. Aydilek).www.elsevier.com/locate/wasmanWaste Management 26 (2006) 932–945Goodhue et al., 2001), landfill liners (Abichou et al.,1998, 2004), asphalt concrete (Javed and Lovell, 1995),flowable fill (Bhat and Lovell, 1996), and pavementbases (Kleven et al., 2000). Other studies have shownthat the thermal or biological remediation of the foun-dry sands provides a n opportunity for their land appli-cations (Leidel and Novakowski, 1994; Reddi et al.,1996).Existing research has shown that foundry sand can beeffectively used in geotechnical construction due to itscomparable properties with sand-bentonite mixtures(Abichou et al., 2004). However, limited information ex-ists about the use of foundry sand as a component inbase or subbase layers of highway pavements. Roadwayapplications provide an opportunity for high volume re-use of the excess material. Moreover, the effect of differ-ent factors on the mechanical properties of the subbaselayers constructed with foundry sand need to be evalu-ated. These factors are mainly due to differences in con-structional operations (e.g., compaction conditions),material homogeneity, and the selection of differentmaterials amended with foundry sand.The objective of this study was to investigate the ben-eficial reuse of foundry sand amended mixtures for sub-base layers in highways. To achieve this objective, abattery of tests was conducted on foundry sand androck-foundry sand mixtures amended with lime or ce-ment. Unconfined compressive strength (qu) and Cali-fornia bearing ratio (CBR) tests as well as scanningelectron microscopy (SEM) analyses were conductedto investigate the effect of cement and lime addition, cur-ing time, mo lding water content, and mixture gradationon geotechnical parameters. The effect of winter condi-tions was examined by performing hydraulic conductiv-ity and unconfined compression tests on the specimensafter a series of freeze–thaw cycles. Finally, the environ-mental suitability of the prepared mixtures was evalu-ated through leaching tests.2. MaterialsThe foundry sand us ed in this study was obtainedfrom Toprak Foundry located in Bilecik, Turkey. Thefoundry sand had approximately 24% particles passingthe US No. 200 sieve (<0.074 mm) and was classifiedas nonplastic silty sand (SM) according to the UnifiedSoil Classification System (USCS) and A-2-4 accordingto the American Associat ion of


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