1,720,984 research outputs found
Effects of carbonation on chemo-mechanical behaviour of lime-treated soils
No full textIn the paper, a multi-scale experimental investigation on the occurrence of carbonation and its effect on chemo-mechanical behaviour of lime-treated soil has been presented. Carbonation affects chemo-mineralogical evolution of lime-treated soils depending on the time scale at which reaction mechanism takes place. In the short term, a progressive carbonation of portlandite is responsible for the formation of calcium carbonate with consumption of available lime for pozzolanic reactions (lime carbonation). In the long term, carbonation of the secondary phases resulting from pozzolanic reactions weakens the bonding effects induced by hydrated compounds (carbonation of secondary reaction products). Mineralogical and microstructural features of lime-treated and carbonated samples have been monitored at increasing curing times by means of microstructural analyses. Triaxial drained compression tests have been performed on treated samples cured in different conditions for short and long term. Mineralogical investigations showed precipitation of calcium carbonate for lime-treated samples exposed to atmospheric CO2 since the very short term. Exposure of lime-treated sample to CO2 after precipitation of hydrated phases favoured decalcification of cementitious compounds and formation of calcium carbonate. In both cases, precipitation of calcite relevantly affects the mechanical behaviour of lime-treated samples. From the observed behaviours, it will be possible to take into account relevant factors for performing the best practice finalized to efficient and durable soil treatment
Microstructural evolution and mechanical behaviour of alkali activated fly ash binder treated clay
No full textThis work focuses on the use of alkali activated fly ash-based binder to enhance engineering characteristics of soft clay-rich soils and as a substitute to standard stabilisers (e.g., lime or cement). Especially, it examines the microstructural evolution of a calcium-rich fly ash from coal combustion-based binder activated by a sodium-based alkaline solution. To this end, the processes generating the microstructure and the evolution of the pore network over time are investigated. A second point addressed by this study is how the presence of kaolin particles affects the microstructural features of the binder. The microstructure has therefore been investigated by considering the binder alone and the binder mixed with kaolin. The effects of microstructural evolution have been observed at macroscopic level by means of one-dimensional compression tests. The combination of completing techniques has been used including Optical microscopy, Scanning Electron Microscopy and Mercury Intrusion Porosimetry in order to gain an overview of the complex pore structure. Microstructural changes occur around calcium-containing phases derived from fly ash which are the reactive phases of the system. Namely, the dissolution of calcium-rich grains leads to the formation of new compounds that first cover the grain surfaces and then further grow into the available space. Furthermore, the evolution of the pore network over time is characterized by a progressive filling of capillary pores by new compounds while small nanometric pores are being formed and associated with the newly formed silicate-calcium chains. Similar tendencies are observed when the binder is mixed with the soil although the general porosity is lesser due to the filling of pores by small-sized kaolinite platelets. Experimental evidences at microscale level have been linked to the macroscopic behaviour of treated soil
Physical properties and mechanical behavior of a soil treated with fluidal fly ash and lime
No full textMechanical behaviour of compacted kaolin clay stabilised via alkali activated calcium-rich fly ash binder
No full textUse of Alkali-Activated Fly Ashes for Soil Treatment
No full textThe use of alkali-activated fly ashes (AAFA) to improve engineering properties of clayey soils is a novel solution, alternative to the widely diffused improvement based on the use of traditional binders such as lime and cement. An experimental investigation on chemo-physical evolution of alkali-activated binders and their use for soil improvement has been developed. Treated samples were prepared by mixing soil and fly ash with water and alkaline solution and dynamically compacted. Mechanical behaviour has been investigated by means of triaxial tests performed on treated samples compacted at optimum water content. Addition of alkali activated binder increased stiffness and shear strength of treated samples, whose extent depends on binder content and curing time
Multi-scale analysis on soil improved by alkali activated binders
No full textIn the present paper, the use of alkali activated binders to improve engineering properties of clayey soils is presented as an alternative to traditional binders such as lime or cement. An alkali-activated fly ash and its chemo-physical evolution has been monitored at increasing curing times by means of X-Ray Diffraction and Scanning Electron Microscopy. Alkali-activated binder has been mixed with soil for evaluating the improvement of its mechanical behaviour. One-dimensional compression tests on treated samples have been performed with particular reference to effects induced by binder content and curing time. Test results showed a high initial reactivity of the alkali activated systems promoting formation of new mineralogical phases responsible of the mechanical improvement of the treated soil
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