Environmental suitability of recycled concrete aggregate in highways.

PDFTech ReportMD-15-SP109B4G-2SP109B4GPavement designAggregate gradationConcrete aggregatesRecycled materialsLaboratory testsModulus of resilienceDeformationDurabilityCalifornia bearing ratioFreeze thaw testsLeachingStiffnessMarylandMaryland. State Highway Administration. Office of Policy & ResearchAydilek, Ahmet H.University of Maryland (College Park, Md.)US Transportation CollectionThe use of recycled concrete aggregate materials in highway constructions as compared to the use of virginmaterials reduces virgin natural resource demands on the environment. In order to evaluate their potential use ofrecycle materials in highway construction, two different recycled concrete aggregate (RCA) materials and twoconventional graded aggregate base (GAB) materials and the mixtures of RCA-GAB materials were tested in thelaboratory for their strength (California Bearing Ratio), resilient modulus, permanent deformation, and durability. Inaddition, laboratory water leach tests (WLTs), and pH-dependent leaching tests were conducted to determine theenvironmental suitability of RCA materials. The leaching behavior of Ca, Cr, Cu, Fe, and Zn from RCAs and theeffects of pH, curing time, freeze/thaw cycles, liquid-to-solid ratio, and particle size on leaching of these metals wereinvestigated. The summary resilient moduli (SMR) of RCAs were 2.6 and 2 times higher than that of the naturalGAB material and their stiffness increased when subjected to freezing and thawing cycles. Consistent trend couldnot be observed with CBR and SMR values and percent RCA addition. Overall, GAB yielded lower permanentdeformations compared to the RCA materials. In pH-dependent leaching tests, Ca showed cationic leaching patterns,while Cr, Cu, Zn, and Fe showed amphoteric leaching patterns. Leaching tests results indicated that leached Znconcentrations were below the detection limits at pH>5. Increasing curing time caused rehydration of cementparticles and generally yielded a decrease in pH and leached concentrations of metals. Freezing and thawing ofRCA also led to self-cementing and decreased pH, Ca concentrations while no consistent trends were found betweenthe leaching of Cr, Cu, and Fe concentration and freeze-thaw cycles. Increasing the liquid-to-solid ratio decreasedleaching of elements significantly due to the dilution of leached elements in the aqueous solutions