Physical Performance of Cement-Treated Silty Sand Soil under Cycles of Freezing/Thawing

Reza Jolous Jamshidi, Craig B. Lake, Chris Barnes, Colin D. Hills, Peter Gunning

In the proceedings of: GEO2011: 64th Canadian Geotechnical Conference, 14th Pan-American Conference on Soil Mechanics and Geotechnical Engineering, 5th Pan-American Conference on Teaching and Learning of Geotechnical Engineering

Session: Geoenvironmental Engineering

ABSTRACT: Cement-based solidification/stabilization (S/S) is becoming an increasingly used technology for treatment of a wide range of contaminants. Current design of S/S remediation systems to resist freeze/thaw (f/t) cycles is based on tests available for soil-(rather than its hydraulic properties) as the resistibility indicator. This paper studies the effect of f/t cycles on physical performance of a silty sand soil solidified by addition of 10 percent Portland cement. Changes in the hydraulic conductivity, dynamic properties and micro-structure of the specimens were monitored after exposure to different levels of f/t. Results show a considerable amount of damage to the structure of the monolith after 7 cycles of f/t. An increase of up to two orders of magnitude in the hydraulic conductivity of the specimens was observed. Also changes in the dynamic properties of the specimens suggest the proposed technique may be suitable for detection of performance change due to f/t exposure.

RÉSUMÉ: La solidification/stabilisation ciment-basé (le S/S) devient une technologie de plus en plus utilisée pour le traitement d'une grande variété de contaminants. La conception actuelle de systèmes de redressement de S/S pour résister le gèle/dégel (f/t) les cycles sont fondés sur les tests disponibles pour le sol-ciment qui considère l'intégrité de l'échantillon (au lieu de ses propriétés hydrauliques) comme l'indicateur de resistibility. Ce papier étudie l'effet de cycles de f/t sur l'exécution physique d'un sol de sable de silty solidifié par l'addition de ciment de Portland de 10 pourcent. Les changements dans la conductivité hydraulique, les propriétés et la micro-structure dynamiques des spécimens ont été contrôlées après l'exposition aux niveaux différents de f/t. Les résultats montrent beaucoup de dommages à la structure du monolithe après 7 cycles de f/t. Une augmentation de jusqu'à deux ordres de magnitude dans la conductivité hydraulique des spécimens ont été observés. Aussi les changements dans les propriétés dynamiques des spécimens suggèrent que la technique proposée peut être convenable pour la détection de changement d'exécution en raison de l'exposition de f/t. 1. INTRODUCTION Cement based solidification/stabilization (S/S) is a well-established remediation technology for the treatment of a wide range of contaminated soils/sludge (Paria and Yuet, 2006). The general technique of this technology involves mixing waste/contaminated soil with a binder (cement or other supplementary materials such as fly ash, furnace slag, etc.) to immobilize the contaminants in the structure of the resulting monolith (Bone et al., 2004). Immobilization of contaminants can occur as a result of changes in physical properties of the waste material (i.e. solidification) and/or chemical changes in the contaminant/matrix (i.e. stabilization) (Batchelor, 2006). Because of the potential advantages of this technology (i.e. economics, soil improvement, risk reduction, etc.), considerable research has been performed to investigate the effectiveness of the technology for treatment of different types of contaminants (e.g.: Chan et al., 2000; Silva et al., 2007, Leonard and Stegmann, 2010). However, little research has been published related to evaluation of the long term performance of this technology in cold regions where it is prone to exposure to cycles of freezing and thawing (f/t). Freeze/thaw can occur either during the construction phase of the project (i.e. prior to cover system placement), or at some point during the design life; when the cover system fails to fulfill its purpose as an insulation barrier. Both of these scenarios are a concern for Canada, as cement-based S/S projects have received increased attention in recent years for the remediation of Brownfield sites (e.g. The Sydney Tar Ponds remediation project, Sydney, Nova Scotia). Despite the lack of experience on the performance of cement-based S/S monolith materials subjected to f/t, there is considerable research related to the f/t effects on compacted clays for landfill applications (e.g.: Othman and Benson, 1992; Othman and Benson, 1993), soil-cement for transportation applications (e.g.: Yarbasi et al., 2007; Shihata and Baghdadi, 2001; Kettle, 1986) and concrete (e.g.: Penttala 2006; Micahhale et al., 2009). Generally, the understanding of a cement-based material exposed to sub-zero temperatures is that initially the water in large pores (entrapped/entrained pores) and subsequently capillary pores will freeze (Chatterji, 2003). Freezing of water results in an increase in the initial volume and this can create internal forces within the structure (Chatterji, 2003) which potentially can cause damage of the cement-based material.

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