نفوذ پذیری هیدرولیکی رس دریایی تثبیت شده با سیمان به همراه متاکائولین و ارتباط آن با توزیع اندازه حفرات Hydraulic conductivity of cement-stabilized marine clay with metakaolin and its correlation with pore size distribution

Calcinations of pure kaolinite at temperatures from 550 °C to 900 °C produce an amorphous silica compound (metakaolin, i.e., MK), which is a very reactive aluminosilicate pozzolan (Janotka et al., 2010) and is usually used as a mineral additive in the cement and concrete (Qian and Li, 2001; Vejmelková et al., 2010). Caldarone et al. (1994), Wild and Khaitib (1996), Curcio et al. (1998) and Poon et al. (2001) found that the MK agent could obviously improve the early strength and that at a preset period whatever concretes or mortars. Boddy et al. (2001) and Gruber et al. (2001) found that the permeability of the Cl− ion of the concrete with the MK agent sharply decreases which means the better concrete durability under sea water environments. Cassagnabère et al. (2011) compared the strength and durability of mortars with pure cement and those with ternary binders (cement + slag + metakaolin) in the view of the water absorption and oxygen permeability, and confirmed the MK’s effectiveness and environmental friendship. Above all, the former researches showed the applicability and effectiveness of MK agent in concretes and mortars. It should be mentioned that the MK was also used as an agent to cement-based stabilized clays, as Kolovos et al. (2013) and Zhang et al. (2014) reported the application in the grouting and deep mixing projects respectively. The deep mixing method is another kind of ground improvement techniques to treat the soft clays and has been widely applied in China, Japan and Europe, where the soft clay and cement (in the form of a powder or slurry) are mixed by machines in situ. In the design of the deep mixing method, the strength and hydraulic conductivity of cemented soils should be both considered. Even though the MK effectiveness in strength of the cemented soils was reported (Zhang et al. (2014)), the MK effect on hydraulic conductivity is still not clear and needs to be further investigated. The former researches on the hydraulic conductivity of pure cement stabilized soils and that of clays may help us perform this study. Terashi and Tanaka (1983) found that it decreased with the cement content while Chew et al. (2004) proposed that the hydraulic conductivity should be associated with the void ratio. The experiments of Broderic and Daniel (1990), Locat et al. (1996) and Lorenzo and Bergado (2006) confirmed the same results as Chew et al. (2004). Note that despite the relationship between the hydraulic conductivity and void ratio respectively existed for a kind of cemented soils, the statistical relationship appeared to be much dispersed when all data gathered. Additionally, there is also no relatively unique relationship between the permeability and void ratio or clay fraction even though Tavenas et al. (1983) discussed that of clays. To uniform the relationships of clays, micro pore size distribution was taken into account according to the Poiseuille’s theory for laminar flow though porous media (Childs and Collis-George, 1950) and several models have been developed to this end (capillary models, hydraulic-radius model, probabilistic models, summarized by Lapierre et al. (1990)). Since the pore size distribution by the mercury intrusion porosimetry (MIP) explicates the characterization of the entrance throat pore size and the cumulative pore volume, representative parameters of the functions must be selected for further analyzing, where Garcia-Bengochea et al.(1979), Juang and Holtz (1986) and Tanaka et al. (2003) did important works. Among them, Tanaka et al. (2003) proposed a relative simple combined variable (nD502 , where n is soil porosity and D50 is the median diameter of entrance pores when 50% of the total cumulative pore is attained in MIP tests) and tried to uniform the hydraulic conductivity of clays. As the cemented soils with or without MK can be both classified to special soils and cement-based reinforced materials, the applicability of the empirical expressions of the hydraulic conductivity from clays, cement stabilized soils and concretes needs to be further evaluated. To understand the percolation behavior of cemented soils and MK effect on the hydraulic conductivity, ordinary Portland cement (OPC) and MK were first prepared and mixed at various mass ratios, and then this mixture was then remixed with Lianyungang marine clay (a type of marine clay typically deposited in the eastern China; Deng et al., 2014) to obtain the cement stabilized soils. After curing at standard conditions according to the standard ASTM D1632 (2007), the percolation and MIP tests were performed to investigate the MK and micropore effect on the hydraulic conductivity. Furthermore, the data of the hydraulic conductivity and pore size distribution of the clays, cement stabilized soils, cement pastes and concretes are gathered to discuss and statistically evaluate the empirical expressions, which can be used for predicting and revealing the mechanism of percolation behavior of these materials.