Research paper Strength development in soft marine clay stabilized by fly ash and calcium carbide residue based geopolymer Chayakrit Phetchuay a , Suksun Horpibulsuk b, ⁎, Arul Arulrajah c , Cherdsak Suksiripattanapong d, ⁎⁎, Artit Udomchai b a School of Civil Engineering, Suranaree University of Technology, 111 University Avenue, Muang District, Nakhon Ratchasima 30000, Thailand b School of Civil Engineering and Center of Excellence in Innovation for Sustainable Infrastructure Development, Suranaree University of Technology, Thailand c Department of Civil and Construction Engineering, Swinburne University of Technology, Hawthorn, VIC 3122, Australia d Program in Civil Engineering, Faculty of Engineering and Architecture, Rajamangala University of Technology Isan, 744 Suranarai Road, Muang District, Nakhon Ratchasima 30000, Thailand abstract article info Article history: Received 6 February 2016 Received in revised form 4 April 2016 Accepted 5 April 2016 Available online 29 April 2016 This research investigates strength development and the carbon footprint of Calcium Carbide Residue (CCR) and Fly Ash (FA) based geopolymer stabilized marine clay. Coode Island Silt (CIS), a soft and highly compressible ma- rine clay present in Melbourne, Australia was investigated for stabilization with the CCR and FA geopolymers. CCR is an industrial by-product obtained from acetylene gas production, high in Ca(OH) 2 and was used as a green ad- ditive to improve strength of the FA based geopolymer binder. The liquid alkaline activator used was a mixture of sodium silicate solution (Na 2 SiO 3 ) and sodium hydroxide (NaOH). The influential factors studied for the geopolymerization process were Na 2 SiO 3 /NaOH ratio, NaOH concentration, L/FA ratio, initial water content, FA content, CCR content, curing temperature and curing time. The strength of stabilized CIS was found to be strongly dependent upon FA content and NaOH concentration. The optimal ingredient providing the highest strength was found to be dependent on water content. Higher water contents were found to dilute the NaOH concentration, hence the optimal L/FA increases and the optimal Na 2 SiO 3 /NaOH decreases as the water content present in the clay increases. The maximum strength of the FA geopolymer (without CCR) stabilized CIS was found at Na 2 SiO 3 /NaOH = 70:30 ratio and L/FA = 1.0 for clay water content at liquid limit (LL). The role of CCR on the strength of FA geopolymer stabilized CIS can be classified into three zones: inactive, active and quasi-inert. The active zone where CCR content is between 7% and 12% is recommended in practice. The 12% CCR addition can im- prove up to 1.5 times the strength of the FA geopolymer. The carbon footprints of the geopolymer stabilized soils were approximately 22%, 23% and 43% lower than those of cement stabilized soil at the same strengths of 400 kPa, 600 kPa and 800 kPa. The reduction in carbon footprints at high strength indicates the effectiveness of FA geopolymer as an alternative and effective green soil stabilizer to traditional Portland cement. © 2016 Elsevier B.V. All rights reserved. Keywords: Geopolymer Strength Coode Island Silt Fly Ash Calcium Carbide Residue Marine clay Carbon footprint 1. Introduction The eastern part of Melbourne's Central Business District is located in the Yarra Delta, which is a low-lying area of soft marine and estuarine quaternary deposits with high groundwater levels. These characteristics have historically resulted in a large area of land near the city center re- maining under-developed. However, this previously under-developed space is now experiencing a rebirth following a directive by the local state government to rehabilitate it to accommodate extension of existing port facilities, cater for the growth of the port of Melbourne as a large container center as well as to provide space for industry and wa- terfront residential development (Bouazza et al., 2004). The existence of a soft (undrained shear strength in the range of 5– 30 kPa) and highly compressible layer of marine sediment, Coode Island Silt (CIS), in the Yarra Delta however imposes geotechnical constraints on the design and performance of future infrastructure works. Deposits of CIS extend to depths of upto 30 m. Regardless of the magnitude of the applied loads, total and differential settlements in the range of 500– 700 mm were expected for shallow foundation supported structures built on CIS (Ervin, 1992). The traditional engineering solution is deep foundation (pile) to transfer loads through the soft clay to deeper and stiffer layers. However, this solution is expensive and may not suit for low to medium load bearing structures. Several ground improvement techniques dealing with soft soil foun- dation have been developed over the past 30 years (Bergado et al., 2003; Bouazza et al., 2006; Arulrajah and Bo, 2008; Horpibulsuk et al., 2012c; Shen et al., 2013a, 2013b, 2013c; Du et al., 2013, 2014; Chai et al., 2014; Applied Clay Science 127–128 (2016) 134–142 ⁎ Correspondence to: School of Civil Engineering, Suranaree University of Technology, 111 University Avenue, Muang District, Nakhon Ratchasima 30000, Thailand. ⁎⁎ Correspondence to: Program in Civil Engineering, Rajamangala University of Technology Isan, 744 Suranarai Road, Muang District, Nakhon Ratchasima 30000, Thailand. E-mail addresses: suksun@g.sut.ac.th, suksun@sut.ac.th (S. Horpibulsuk), cherdsak.su@rmuti.ac.th (C. Suksiripattanapong). http://dx.doi.org/10.1016/j.clay.2016.04.005 0169-1317/© 2016 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Applied Clay Science journal homepage: www.elsevier.com/locate/clay