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Cell-free soil bio-cementation with strength, dilatancy and fabric characterization
Ist Teil von
Acta geotechnica, 2019-06, Vol.14 (3), p.639-656
Ort / Verlag
Berlin/Heidelberg: Springer Berlin Heidelberg
Erscheinungsjahr
2019
Link zum Volltext
Quelle
Alma/SFX Local Collection
Beschreibungen/Notizen
A multi-disciplinary approach is adopted in the present work towards investigating bio-cemented geo-materials which extends from sample preparation, to microstructural inspection and mechanical behaviour characterization. We suggest a new way to induce “cell-free” soil bio-cementation along with a comprehensive description of bio-improved mechanical and microstructural properties. We utilize the soil bacterium
Sporosarcina Pasteurii
in freeze-dried, powder—instead of vegetative—, state and determine overall reaction rates of “cell-free” microbial-induced calcite (CaCO
3
) precipitation (MICP). We further investigate strength and stiffness parameters of three base geo-materials which are subjected to MICP under identical external bio-treatment conditions. Different trends in the mechanical response under unconfined and drained triaxial compression are obtained for fine-, medium- and coarse-grained sands for similar range of final CaCO
3
contents. Pre- and post-yield dilatancy–stress relationships are obtained revealing the contribution of dilatancy in the achievement of peak strength. Medium-grained sand yields higher dilatancy rates and increased peak strength with respect to fine-grained sand. Further, insight into the bio-cemented material’s fabric is provided through scanning electron microscopy, time-lapse video microscopy and X-ray micro-computed tomography with subsequent 3D reconstruction of the solid matrix. A qualitative description of the observed precipitation behaviours is coupled with quantified microscopic data referring to the number, sizes, orientations and purity of CaCO
3
crystals. Results reveal that MICP adapts differently to the adopted base materials. Crystalline particles are found to grow bigger in the medium-grained base material and yield more homogenous spatial distributions. Finally, a new workflow is suggested to ultimately determine the crucial contact surface between calcite bonds and soil grains through image processing and 3D volume reconstruction.