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This paper describes the strength and microstructural behaviour of lime–slag-treated clay. The microstructure was investigated using X-ray diffraction (XRD) and scanning electron microscopy (SEM), and the strength of the treated clay was measured using the unconfined compressive strength (UCS) test. Untreated clay was prepared in the laboratory by mixing commercially available kaolin and bentonite, while hydrated lime and ground granulated blastfurnace slag (ggbs) were used as binders. XRD analyses of lime–slag-treated clay showed the existence of numerous reaction products such as calcium silicate hydrate (C–S–H), calcium aluminium silicate hydrate (C–A–S–H), and hydrotalcite (HT), which facilitated the strength increment. For a fixed proportion of lime, the relative intensity of pozzolanic reaction products was found to increase with increasing slag content. Slag was found to be very active to promote the pozzolonic reaction with lime, as evidenced from the presence of crystalline reticular (C–S–H) and platy (C–A–S–H) cementitious products in the SEM images. The role of lime in the activation of slag was also seen to have an upper limit whereby excess proportions failed to provide significant additional benefit. The UCS of lime–slag-treated clay was found to be higher in comparison with lime or slag alone with the same replacement ratio. This was due to the formation of more crystalline cementitious products, which accelerated the bridging (cementation) effect between lime–slag and clay particles.

This paper examines the microstructural behaviour of cement-treated soft Singapore marine clay. The microstructure was investigated using X-ray diffraction, (XRD) scanning electron microscopy, (SEM) mercury intrusion porosimetry, and laser diffractometric measurement of particle size distribution. The XRD analysis of cement-treated clay enables the identification of the formation of cementitious products, namely calcium silicate hydrate (CSH) and calcium aluminium silicate hydrate (CASH). The relative amount of cementitious products (CSH + CASH) is found to increase with increase of the cement content. The fabric of the treated clay changes to flocculated type, comprising clay-cement clusters separated by large intercluster voids with smaller intra-cluster pores, as can be seen from the SEM images of treated clay. This change is more pronounced with higher cement content and prolonged curing time. The flocculation of the clay particles also causes water to be trapped within the clay-cement cluster and increases both the effective size of the particles or cluster and the entrance pore diameter. This understanding clearly helps to explain the observed engineering behaviour of cement-treated clays commonly found in deep cement mixing or jet grouting techniques. Cet exposé examine le comportement microstructural d'une argile marine tendre de Singapour traitée au ciment. Nous avons étudié sa microstructure en utilisant une diffraction de rayons X, une microscopie électronique à balayage, une porosimétrie à intrusion de mercure et des mesures de diffractométrie laser pour la répartition de dimensions de particules. L'analyse XRD de l'argile traitée au ciment permet d'identifier la formation de produits cimenteux, nommément d'hydrate de silicate de calcium (CHS) et d'hydrate de silicate d'aluminium calcium (CASH). Il est apparu que la quantité relative de produits cimenteux (CSH + CASH) augmentait en même temps que la teneur en ciment. La structure de l'argile traitée devient floculée et comporte des noyaux d'argile-ciment séparés par de grands vides entre les noyaux et avec de pores plus petits à l'intérieur des noyaux. Ce changement est plus prononcé lorsque le contenu de ciment est plus élevé et que le temps de cuisson est plus long. La floculation des particules d'argile a pour effet de piéger l'eau à l'intérieur des noyaux argile-ciment et augmente à la fois la dimension effective des particules ou du noyau et le diamètre de pore d'entrée. Cette constatation aide clairement à expliquer le comportement mécanique observé des argiles traitées au ciment utilisées couramment dans les techniques de mixage profond ou d'injection de ciment.

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