Unsaturated hydraulic properties of cemented tailings backfill that contains sodium silicate

Abstract Recycling the mine waste (tailings) into cemented tailings backfill has economical and environmental advantages for the mining industry. One of the most recent types of cemented tailings backfill is gelfill (GF), a backfill that contains sodium silicate as chemical additive. GF is typically made of tailings, water, binder and chemical additives (sodium silicate gel). It is a promising mine tailings backfill technology. From a design point of view, the environmental performance or durability of GF structures is considered as a key factor. Due to the fact that GF structures are cementitious tailings, their durability and environmental performance depend on their ability to resist the flow of aggressive elements (water and oxygen). Thus, understanding the unsaturated hydraulic properties of GF is essential for a cost-effective, environmentally friendly and durable design of GF structures. However, there is a lack of information with regards to unsaturated hydraulic properties of GF, the factors that affect them and their evolution with time. Hence, the unsaturated hydraulic properties (water retention curve (WRC) or water characteristic curve, air entry value (AEV), residual water content, unsaturated hydraulic conductivity) of GF are investigated in this paper. GF samples of various compositions and cured in room temperature for different times (3, 7, 28, and 90 days) are considered. Saturated hydraulic conductivity and microstructural tests have been conducted; WRCs are measured by using a WP4-T dewpoint potentiameter and the saline solution method. Unsaturated hydraulic conductivity is predicted using the van Genuchten (1980) equation. The water retention curve (WRC) is determined as the relationship between volumetric water content and suction for each GF mix and curing time. The van Genuchten (1980) equation is used to simulate the WRC to best-fit the experimental data. AEV and residual water content are also computed for each mix and curing time. Furthermore, functions are developed to predict the evolution of AEVs, residual water content and fitting parameters of the van Genuchten model with degree of hydration. Important outcomes have been achieved with regards to unsaturated hydraulic properties. The unsaturated hydraulic conductivity of GF was calculated to decrease when the suction, binder content, and degree of hydration increase. The effects of binder content and degree of hydration are more obvious at low suction ranges. The obtained results would contribute to a better design and assessment of the durability and environmental performance of GF structures.

[1]  M. Fall,et al.  A contribution to understanding the effects of curing temperature on the mechanical properties of mine cemented tailings backfill , 2010 .

[2]  R. H. Brooks,et al.  Hydraulic properties of porous media , 1963 .

[3]  Delwyn G. Fredlund,et al.  Development and verification of a coefficient of permeability function for a deformable unsaturated soil , 1998 .

[4]  Christian Roth,et al.  A new laboratory method to quickly determine the unsaturated hydraulic conductivity of undisturbed soil cores within a wide range of textures. , 1990 .

[5]  D. G. Fredlund,et al.  Wetting front advancing column test for measuring unsaturated hydraulic conductivity , 2009 .

[6]  Günther Meschke,et al.  NUMERICAL MODELING OF COUPLED HYGROMECHANICAL DEGRADATION OF CEMENTITIOUS MATERIALS , 2003 .

[7]  Olivier Coussy,et al.  Characterization and identification of equilibrium and transfer moisture properties for ordinary and high-performance cementitious materials , 1999 .

[8]  V. Baroghel-Bouny,et al.  Pore Structure and Moisture Properties of Cement-Based Systemsfrom Water Vapour Sorption Isotherms , 1994 .

[9]  D C Sego,et al.  Laboratory properties of mine tailings , 2001 .

[10]  M. Fall,et al.  Modeling the heat development in hydrating CPB structures , 2009 .

[11]  Bonnie Mae Savage,et al.  Soil physics principles validated for use in predicting unsaturated moisture movement in portland cement concrete , 1997 .

[12]  Feike J. Leij,et al.  Closed‐Form Expressions for Water Retention and Conductivity Data , 1997 .

[13]  Mamadou Fall,et al.  Effect of high temperature on strength and microstructural properties of cemented paste backfill , 2009 .

[14]  R. Weyers,et al.  Development of concrete shrinkage performance specifications. , 2003 .

[15]  Mamadou Fall,et al.  Mix proportioning of underground cemented tailings backfill , 2008 .

[16]  D. Fredlund,et al.  Mathematical attributes of some soil–water characteristic curve models , 2001 .

[17]  Ning Lu,et al.  Unsaturated Soil Mechanics , 2004 .

[18]  D. Fredlund,et al.  Predicting the permeability function for unsaturated soils using the soil-water characteristic curve , 1994 .

[19]  Y. Mualem.  A New Model for Predicting the Hydraulic Conductivity , 1976 .

[20]  A. Neville.  Properties of Concrete , 1968 .

[21]  Yu-Jun Cui,et al.  Determining the unsaturated hydraulic conductivity of a compacted sand-bentonite mixture under constant-volume and free-swell conditions , 2008 .

[22]  Harianto Rahardjo,et al.  PERMEABILITY FUNCTIONS FOR UNSATURATED SOILS , 1997 .

[23]  Dale P. Bentz,et al.  A review of early-age properties of cement-based materials , 2008 .

[24]  D. Fredlund,et al.  Soil Mechanics for Unsaturated Soils , 1993 .

[25]  J. Beaudoin.  Effect of humidity and porosity on fracture of hardened portland cement , 1982 .

[26]  Sandra L. Houston,et al.  Protocol for the assessment of unsaturated soil properties in geotechnical engineering practice , 2009 .

[27]  G. W. Snedecor.  Statistical Methods , 1964 .

[28]  S. Khattab,et al.  Strength, Durability And Hydraulic Properties Of Clayey Soil Stabilized With Lime And Industrial Waste Lime , 2008 .

[29]  W. R. Gardner,et al.  MATHEMATICS OF ISOTHERMAL WATER CONDUCTION IN UNSATURATED SOIL , 1958 .

[30]  Pierre Delage,et al.  Experimental unsaturated soil mechanics , 2002, 0803.1434.

[31]  Steven G. Vick,et al.  Planning, design, and analysis of tailings dams , 1983 .

[32]  Mamadou Fall,et al.  Mechanical response of a mine composite material to extreme heat , 2008 .

[33]  Paul Simms,et al.  Evaporation, Unsaturated Flow, and Salt Accumulation in Multilayer Deposits of “Paste” Gold Tailings , 2010 .

[34]  Van Genuchten,et al.  A closed-form equation for predicting the hydraulic conductivity of unsaturated soils , 1980 .

[35]  Mamadou Fall,et al.  Pore structure of cemented tailings materials under natural or accidental thermal loads , 2008 .

[36]  Henry Jean Claude Celestin.  Geotechnical properties of cemented paste backfill and tailings liners: Effect of mix components and temperature , 2009 .

[37]  Mamadou Fall,et al.  Shear behaviour of cemented pastefill-rock interfaces , 2008 .

[38]  Olivier Coussy,et al.  ROLE OF AIR PRESSURE IN DRYING OF WEAKLY PERMEABLE MATERIALS , 2001 .

[39]  Mamadou Fall,et al.  Saturated hydraulic conductivity of cemented paste backfill , 2009 .

[40]  M. Crawley.  Non‐linear Regression , 2007 .

[41]  N. T. Burdine.  Relative Permeability Calculations From Pore Size Distribution Data , 1953 .

[42]  Wilfried Brutsaert,et al.  PROBABILITY LAWS FOR PORE-SIZE DISTRIBUTIONS , 1966 .

[43]  D. Fredlund,et al.  Equations for the soil-water characteristic curve , 1994 .

[44]  Gregory B. Davis,et al.  A model of oxidation in pyritic mine wastes: part 1 equations and approximate solution , 1986 .

[45]  A. Ehrlacher,et al.  Analyses and models of the autogenous shrinkage of hardening cement paste: I. Modelling at macroscopic scale , 1995 .

[46]  S. Lee Barbour,et al.  Nineteenth Canadian Geotechnical Colloquium: The soil-water characteristic curve: a historical perspective , 1998 .

[47]  Farid Benboudjema,et al.  Analysis of microcracking induced by differential drying shrinkage , 2008 .