Influence of compaction water content on the hydraulic conductivity of sand- bentonite and zeolite-bentonite mixtures A. H. O ¨ REN 1, *, S. DURUKAN 2 AND A. S° . KAYALAR 1 1 Department of Civil Engineering, Dokuz Eylu ¨l University, 35160, Buca-Izmir, Turkey, and 2 Manisa Organize Sanayi Bo ¨lgesi Vocational School, Celal Bayar University, Manisa, Turkey (Received 12 April 2013; revised 14 February 2014; Editor: George Christidis) A B S T R A C T : Although investigation of the hydraulic conductivity behaviour of zeolite-bentonite mixtures (ZBMs) has been a topic of interest for researchers recently, the influence of compaction water content on the hydraulic conductivity of ZBMs has not been studied so far. This study discusses the hydraulic conductivities of ZBMs and compares the results with those of sand-bentonite mixtures (SBMs). The hydraulic conductivities of SBMs were unaffected by compaction water content and bentonite content, but the hydraulic conductivities of ZBMs were substantially different in mixtures containing 10% and 20% bentonite. The hydraulic conductivity of 10% ZBM (i.e. containing 10% bentonite and 90% wt. zeolite) gradually decreased as the water content increased to optimum water content and then it tended to decrease rapidly when the water content exceeded the optimum. In contrast, the hydraulic conductivity of 20% ZBM sharply decreased at the early stages of compaction water content (i.e. on the dry side of optimum water content) and levelled off when the water content was at the optimum water content. However, there is at least one order of magnitude difference between the hydraulic conductivities of ZBMs and SBMs, supporting the zeolite network model as suggested in previous works. KEYWORDS: bentonitic mixture, compaction, hydraulic conductivity, sand, zeolite. Crack formations in compacted clays (CCs) on building sites constitute a major problem that can be encountered during the post-construction stage (Albrecht & Benson, 2001), leading to uneven volumetric shrinkage of covers and increasing hydraulic conductivities. To reduce the volumetric shrinkage potential of CCs, natural clay-sand mixtures were proposed in mid 1980s (Kleppe & Olson, 1985). However, in practice these mixtures cause uncertainty because the amount of clay that should be used in a mixture depends totally on the mineralogy of the clay component. Thus, smectitic clays, bentonites, have been preferred instead of natural clays. Sand-bentonite mixtures (SBMs) are the most well known bentonitic mixtures, the hydraulic conductivity characteristics of which have widely been investigated (Kenney et al., 1992; Mollins et al., 1996; Stern & Shackelford, 1998; Komine, 2004). Other natural materials, such as zeolites, can also be blended with bentonite to obtain a zeolite-bentonite mixture (ZBM). Zeolites are minerals with negatively charged surfaces and high cation exchange capacity. They contain interconnected pore channels that block the passage of large molecules and thus are referred to as ‘‘molecular sieves’’ (Mumpton, 1999). Zeolites have been utilized as adsorbents for waste-water treatment (Blanchard et al., 1984; Cincotti et al., 2001; Peric et al., 2004; O ¨ ren & Kaya, 2006) and * E-mail: ali.oren@deu.edu.tr DOI: 10.1180/claymin.2014.049.1.09 Clay Minerals, (2014) 49, 109–121 # 2014 The Mineralogical Society