Page 153 - New Trends in Green Construction

PRODUCTION OF NANOSILICA, NANOALUMINA AND NANOTITANIA DISPERSIONS FOR EXTERNAL APPLICATION ON HARDENED MORTARS
Rubén Beltrán, Mercedes Sánchez, FabianoTavares
Keywords: surface treatments, hardened concrete matrix, nanoparticle dispersions. 1. Introduction
Cement-based materials are designed not only to provide mechanical performance to the structures but also to respond to durability demands and to maintain themselves for a certain useful life. Among the main factors that affect the durability of the structures is the presence of water in the concrete, since it is the vehicle through which most of the damage occurs to both the concrete (ice- thaw, attack by sulphates, ...) and to the rebar (corrosion by chlorides ...).
The proposed ongoing research deals with the development of more durable surface treatments, based on the penetration of nanomaterials dispersions through the pores of the concrete. This type of treatment aims to consolidate the cementitious matrix of the treated substrate with compatible products, such as nanosilica dispersions (Sánchez 2014, Franzoni 2014). And taking into account that other types of nanoparticles, such as nanotitania or nanoalumina, can also incorporate different properties to the existing substrate, such as photocatalytic capacity or fire resistance (Xiaoying 2017, part I and part II).
The proposal of the present work involves the production of ad hoc nanoparticle dispersions, to evaluate the influence of significant parameters, such as the size distribution of nanoparticles, the concentration of nanoparticles, the activity of nanoparticles ... and on the effectiveness for consolidating surface treatments and/or improving other properties, such as photocatalytic capacity or fire resistance. (Sánchez 2018)
2. Materials and methods
For this work, the first steep was the synthesis of nanoparticles of Silica, Alumina and Titania by sol gel method. A commercial compound will also be used to compare the differences and the effectiveness of the powders. We made three different mechanical activations (Agate mortar, attritor mill and planetary mill) for obtain nano-size, in order to be able to penetrate inside the pores of the concrete.
Once the nanoparticles have been obtained and correctly characterized, different stable dispersions were prepared for the further application on the mortar-hardened surface. Different dispersions in water media with dispersant agent (ammonium polyacrilate) were made, using ammonium carbonate to obtain a pH near 8-9. This parameter is important because the stabilization of the dispersions depend directly on the pH.
Finally, the prepared dispersions were applied on the concrete samples to evaluate if they were effective and how they functionalize our structure.
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New Trends in Green Construction