Estudo de propriedades de pastas e argamassas cimentícias compostas com vermiculita brasileira (in natura e calcinada).

Abstract

In the vermiculite productionprocessa residue consisting of particles too small to be used commercially is generated. This waste does not have a large-scale applicationyet. An alternative that has been studied is the association with Portland cement in mortar and concrete formulations, as a function of the chemical composition of the residue: high amount of aluminium, silicon and magnesium which may have interactions with the binder. However, the residue has a high specific surface area, in comparison to cement, a fact that can increase the water-demand to mix and limit its application. For this, an alternative is the calcination of this fine residue, as it is done for other clays (kaolin, for example), so that the specific surface area (SSA) is smaller and eventually activates pozzolanic properties in the respective clay. Thus, in this work the various characteristics of cement pastes after addition of vermiculite fine residue were evaluated: chemical reaction, formation of the hydrated products, rheological properties, both after mixing and along the hydration. It was verified that in general the chemical reaction is not affected after the addition of vermiculite, although the formation of aluminates is intensified in the composition with greater amount of in nature residue. Regarding its behaviour in the fresh state, it was observed that the higher SSA of the residue strongly impacts the rheological properties of the pastes, although with a 5% content the changes are minimal. Using these same compositions to evaluate the performance in the hardened state of mortars, it was verified that there is no effect on these properties up to 5% of substitution, regardless of the thermal treatment used. Thus, considering the economic aspects of transport as well as the costs of calcination, it is possible to recommend the addition of 5% of vermiculite in nature without compromising the performance of the products, although it is not possible to determine the its durability during the use.