New evidence for the origin and behaviour of deep ocean 'crusts'

In situ tests in deep waterWest African clays show crust-like shear strengths within the top few metres of sediment. Typical strength profiles show su rising from mud-line to 10 kPa to 15 kPa before dropping back to normally consolidated strengths of 3 kPa to 4 kPa by 1.5m to 2m depth. A Cam-shear device is used to better understand the mechanical behaviour of undisturbed crust samples under pipelines. Extremely variable peak and residual shear strengths are observed for a range of pipeline consolidation stresses and test shear rates, with residual strengths approximating zero. ESEM of undisturbed samples and wet-sieved samples from various core depths show the presence of numerous randomly-located groups of invertebrate faecal pellets. It is therefore proposed that the cause of strength variability during shear testing and, indeed, of the crust's origin, is the presence of random groups of faecal pellets within the sediment. © 2011 Taylor & Francis Group, London.

Characterisation of different commercial reactive magnesia

Reactive magnesia (MgO) has emerged as an essential component in a new family of cements with significantly superior technical and environmental performance over Portland cement. The physical characteristics of different reactive magnesia, which are likely to affect their engineering performance, vary considerably depending on their origin and manufacturing processes. To appropriately utilise such a material, it is essential to develop a better understanding of the characteristics of different magnesia from various sources. In this study, the detailed characterisation of 14 commercial magnesia in terms of reactivity, textural properties, X-ray diffraction pattern, pH value and hydration behaviour and morphology is presented and correlation between them is developed. Relationships were developed between the reactivity, specific surface area, agglomeration ratio and hydration rate based on the experimental observations. As a result, the reactive magnesia used in this study were grouped into three categories and their characteristics and anticipated performances in different applications were discussed.