Developement of Self-Compacting Clay Concrete

Buildings, main pillar of the economy, are of primary importance for the human well-being and fundamental for the modern society. Meantime, the repercussions of the building industry on the environment are immense primarily because of concrete and cement production. Moreover, buildings are one of the main consumers of energy and resources throughout their entire life cycle. In Europe, the building sector is responsible for 42% of the energy consumption, 35% of the greenhouse gas emissions and 50% of the materials extracted. In addition, buildings contribute to waste production, both in the form of unused excavated materials and demolition waste at the end-of-life. In the framework of sustainable growth strategies researched globally, the building sector constitutes one of the main fields where the effort for reducing the environmental impact are concentrated. Many institutions have been researching new strategies to develop low carbon concrete solutions such as geopolymers, limestone calcined clay cement and more. The focus of this dissertation turns towards earth material, because it is locally available, abundant and has a low embodied energy. Furthermore, 1/3 of the global population lives in earthen houses. Despite its advantages and the current challenges of the construction sector, earth is not used as mainstream building material for residential and affordable housings because the mass application of earth is hindered by the vernacular earth construction techniques. Moreover, earthen construction is associated with poverty and low development etc., although architects and engineers are proving the opposite by designing modern earthen architecture, winning worldwide architectural prices and improving the performances of the material. To promote the use of earth as construction material, it is important to develop a process comparable to concrete: fast, easy to use and cheap yet ecofriendly. Consequently, we investigated a strategy to develop a self-compacted clay concrete (SCCC) based on knowledge transfer from material science and concrete technology, and focus on understanding the driving physic-chemicals mechanisms in presence of additives. The preferred process named DeCo process relies on improving and controlling the rheological behavior of clay before and after casting. We report in the manuscript the effect of deflocculants additives such as sodium hexa-metaphosphate and sodium silicate to improve the workability of the clay paste before casting: deflocculation process. Being able to improve the workability of the clay paste is not enough as the paste takes days to dry. To accelerate the hardening, we investigate the use of magnesium and calcium based minerals able to react with the deflocculants: Coagulation process. The results of the investigation show that the combination of deflocculation and coagulation process allow proposing innovative process to develop a SCCC, without relying on hydraulic binders like cement. Furthermore, we highlighted the driving mechanisms of deflocculation and coagulation. We demonstrate in the thesis that, assuming the DLVO theory is applicable in the deflocculated regime, sodium hexametaphosphate disperses clay particles via electrostatic repulsion forces whereas sodium silicate and sodium polyacrylate disperse via electro-steric repulsions forces. In the case of sodium silicate, the dispersion mechanism is controlled by the ratio SiO2/Na2O. When investigating the coagulation process to understand and to control the kinetic of hardening, we stress key factor influencing the hardening at fresh and harden stage. Thanks to rheological and ICP-OES measurements, we show that the coagulants stop the activities of the deflocculants, and the molar ratio coagulant to deflocculant control the kinetic of hardening. Moreover, we observe via SEM and XRD analysis that the coagulant precipitate with the dispersant to form a non-soluble mineral which induce the hardening mechanism to in order to accelerate the demolding. Based on these findings, we compare the DeCo process with the existing strategies available in literatures. For each scenario that allow to develop a SCCC or poured earth concrete, the choice of additives (hydraulic or non-hydraulic binders, coagulants; organic or inorganic deflocculants) and the procedure to introduce them influence the nature of the mechanisms. In fact, assuming that the coagulant is mixed prior with earth, we hypothetise a competitive adsorption of deflocculant as main challenges whereas, through DeCo process, there is a preferential precipitation mineral influencing the hardening process. Further investigations need to be done to differentiate the chemistry and chemical mechanism depending of the steps the chemical agent are introduced. At the end on the dissertation, we successfully demonstrate that the DeCO process helps developing a self-compacted clay based concrete using less than 1% additives and the properties of the final product falls in the range of existing earth materials used for construction. The cost and environmental assessment performed show that the final product reduces 2.5 times the cost and 20 times the carbon footprint with respect to concrete products