Behavior of clay-rich soil /cement mixtures prepared by deep soil mixing method
| Autor: | Myriam Duc, Alain Le Kouby, Fabien Szymkiewicz, Joali Paredes Marino |
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| Přispěvatelé: | Sols, Roches et Ouvrages Géotechniques (IFSTTAR/GERS/SRO), Communauté Université Paris-Est-Institut Français des Sciences et Technologies des Transports, de l'Aménagement et des Réseaux (IFSTTAR), Cadic, Ifsttar |
| Jazyk: | angličtina |
| Rok vydání: | 2019 |
| Předmět: | |
| Zdroj: | international conference-EUROCLAY international conference-EUROCLAY, Jul 2019, PARIS, France. 24 p., graph., photos international conference-EUROCLAY, Jul 2019, Paris, France. 24 p., graph., photos HAL |
| Popis: | international conference - EUROCLAY , Paris, FRANCE, 01-/07/2019 - 05/07/2019; In the hydraulic binder domain, the presence of clay aggregates has been known for a long time to be harmful to hardened mortar or concrete material. However the deep soil mixing technique to reinforce dikes or soils for foundation mixes the existing soil with cement (CEMII or CEMIII). A better understanding of the interaction between anhydrous cement powder, clay and water is therefore required in order to predict the hydraulic or mechanical performances of the soil mixing material and if they match with the targeted values. The present study scanned the properties of cement mixtures with variable natures of clay (4 kaolinites, 2 illites and 1 montmorillonite as well as siliceous sand as reference). The formulation of mixtures aims to obtain the optimum properties with a quantity of cement fixed at 140 kg/m3 which represents around 8% in mass of the soil to be treated. As the quantity of water added to mixture controls the final properties via the appearance of increasing porosity with higher water content, a method based on liquid limit LL is chosen to fix the lower water content to add to achieve a self compacting paste (formulation is positioned at the beginning of the working range). Then, macroscopic material properties are studied in parallel with microstructural characteristics.Globally, the more water sensitive the clay is, the lower the compressive strength UCS of the hardened paste appears. It is important to note that the curing is very slow, ranging from several days to several weeks (during this period mechanical test is not possible). The highest dispersion in UCS is observed with the four tested kaolinitic clays whose behaviors range from that of sand to the one of illite/montmorillonite. It indicated that the clay mineralogy is not the only determining parameter. In each clay family, the cation exchange capacity CEC (or methylene blue value VBS as well as plastic index PI) may vary and such parameters are good indicators to classify clay materials in a first approach. Indeed, CEC reveals not only the clays water sensitivity and then their ability to compete for water during cement hydration, but also their ability to adsorb Ca2+ cations used for CSH precipitation. On the contrary, clays may favor in various proportions the long term pozzolanic effect that allows to reinforce the soil mixing material by additional CSH formation. Furthermore, clays coat the particles of anhydrous cement and by physical screening, they prevent the proper development of a 3D network of CSH that bind neighboring aggregates. In this case, the mechanical properties are impacted by the size of clay aggregates (or balls) linked to the soil preparation method (remoulding,...), and by the clay capacity to disperse in cement mixture. As an example, the low dispersion of illite in cement (favoring aggregates of several tens of microns) increases the performances of mixtures while an intimate mixing at micron scale of kaolinite particles with cement reduces the resistance. Such results may at first seem surprising considering the higher water sensitivity of illite in comparison with kaolinite. |
| Databáze: | OpenAIRE |
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