417 Land Contamination & Reclamation, 18 (4), 2011 © 2011 EPP Publications Ltd DOI 10.2462/09670513.1013 Reuse of water treatment residuals from lime softening, Part II: Characterization of chemically stabilized lime sludge for use in structural fills David J. White, R.J. Baker and J. van Leeuwen Abstract Due to the minimum transportation requirements and the desirability of recycling waste material, lime sludge from water-treatment plants is a candidate for use as fill material in road construction. Using lime sludge for this purpose could present settlement, durability, and strength problems. Therefore, when considering material for use as construction fill, important engineering parameters, including stability and volume change, must be evaluated in order to ensure sound foundations for buildings and roads. The authors investigated dried lime sludge, modified with stabilizers or mixed with soil and other solid materials, as a potential fill material for road construction. Large additions of Portland cement or Class C fly ash to lime sludge generally increase strength values and produce satisfactory unconfined compressive strength results for construction fill. An important limitation of the lime sludge and the stabilized mixtures, however, was the lack of durability through freeze/thaw cycles. Key words: durability, fill material, leaching, lime sludge, settlement, soil stabilization, strength, water treatment residuals 1 INTRODUCTION Road and road-construction densities are greatest near to cities and also, therefore, to water-treatment plants. Due to the minimum transportation requirements and the desirability of recycling of waste material, lime sludge from water-treatment plants is a candidate for use as a fill material in road construction. Using lime sludge for this purpose could present set- tlement, durability, strength and, potentially, leaching problems. Therefore, when considering material for use as construction fill, important engineering parameters, including stability and volume change, must be evalu- ated to ensure sound foundations for buildings and roads. In particular, particle-size distribution, compres- sive strength, shear strength, hydraulic conductivity, and durability in wet/dry and freeze/thaw conditions should be quantified through lab and site testing. Engi- neers can then incorporate this information into the design of embankment fill applications. The authors investigated dried lime sludge, modi- fied with stabilizers or mixed with soil and other solid materials, as a potential fill material for road construc- tion. The purpose of the tests was to define the engi- neering properties of the lime-sludge mixtures. Mixtures of lime sludge, a silty soil (loess), Portland cement, bottom ash, and fly ash were tested. Amounts of stabilizer and moisture were varied within the mix- tures. Selected index properties were investigated. Tests included particle-size analysis and soil classifica- tion, Atterberg limits (liquid and plastic limits and plas- ticity index), moisture–density relationship, unconfined compressive strength (UCS), direct shear, California bearing ratio (CBR), and hydraulic conductivity (flexi- ble wall permeameter). 2 MATERIALS 2.1 Lime sludge The lime sludge used for testing came from the water- treatment plant located in Ames, Iowa. This material Authors David J. White, 1 R.J. Baker 2 and J. van Leeuwen 1 * 1. Department of Civil, Construction, and Environmental Engineering, Town Engineering Building, Iowa State University, Ames, IA 50011, USA 2. FOX Engineering, 414 South 17th Street, Suite 107, Ames, IA 50010, USA * Corresponding author. Tel. 515-294-5251; fax 515-294-8216; email leeuwen@iastate.edu