This paper focuses on the modification of clay properties with inorganic additives to deflocculate and flocculate inorganic soil for the development of a material that would be as easy to use as the current concrete products, but with a much lower environmental impact. Considering that the rheological behaviour of clays is controlled by their surface charge, we first introduce potential determining ions to deflocculate the clay particles and to reduce the yield stress of the earth material. Their efficiency is characterized using zeta potential measurements and rheological tests. We then achieve the flocculation of clay particles by using natural minerals that slowly dissolve in the interstitial liquid and ultimately precipitate calcium silicate hydrate (C–S–H). The precipitation products are identified by X-ray diffraction and the consequences of this delayed precipitation are followed by oscillatory rheometric measurements. Finally, it is suggested that in this process, C–S–H precipitation is not used as a binding vector but as an anti-plasticizer that removes the inorganic dispersant additives.
Thermal
insulators are crucial to reduce the high energy demands
and greenhouse emissions in the construction sector. However, the
fabrication of insulating materials that are cost-effective, fire
resistant, and environmental-friendly remains a major challenge. In
this work, we present a room-temperature processing route to fabricate
porous insulators using foams made from recyclable clays that can
be locally resourced at very low costs. Foams containing either pure
Kaolin or a Kaolin-based clay mixture are produced through mechanical
frothing or an in-situ gas-generating reaction. Surface
modification of the clay particles using a cationic amphiphilic molecule
leads to particle-stabilized foams that are sufficiently strong to
withstand the high capillary stresses developed during water evaporation.
Self-supporting insulators with up to 90% porosity and thermal conductivities
as low as 0.13 W/mK can thus be obtained by simple casting and drying
at ambient temperature in an ultralow energy process. Such materials
can be recycled by crushing, redispersion in water, and subsequent
foaming. Porous structures with higher compressive strength are optionally
created by sintering the dried foams at 1000 °C. The obtained
porous materials perform comparably well with existing fire-resistant
insulators while offering the possibility of closed-loop processing
and wide availability from local resources as well as ultralow cost
and embodied energy.
Abstract. In the ceramic industry and in many sectors, clay minerals are widely used. In earthen construction technique, clay plays a crucial role in the processing. The purpose of this research is to understand and modify the clay properties in earth material to propose an innovative strategy to develop a castable earth-based material. To do so, we focused on the modification of clay properties at fresh state with inorganic additives. As the rheological behaviour of clays is controlled by their surface charge, the addition of phosphate anion allows discussing deep the rheology of concentrated clay suspensions. We highlighted the thixotropic and shear thickening behaviour of a dispersed kaolinite clay suspensions. Indeed, by adding sodium hexametaphosphate the workability of clay paste increases and the behaviour is stable during time after a certain shear is applied. Moreover, we stress that the aging and the shift in critical strain in clay system are due to the re-arrangement of clay suspension and a decrease of deformation during time. The understanding of both effect: thixotropy and aging are crucial for better processing of clay-based material and for self-compacting clay concrete. Yet, studies need to pursue to better understand the mechanism.
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