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COLLOIDAL NANOSILICA AS ADVANCED EXTERNAL REPAIR METHOD FOR CONCRETE STRUCTURES
Mercedes Sánchez, Fabiano Tavares, Ruben Beltrán
Keywords: surface treatment, crack sealing, durability, colloidal nanosilica 1. Introduction
External repair methods based on applying colloidal nanosilica on the hardened concrete surface are proposed for consolidating the existing cementitious matrix and improving the effectiveness and durability of the repair work. Nanosilica is able to penetrate through the concrete pores and to incorporate into the existing solid phases of the existing cementitious matrix (Sánchez, 2014). The compatibility of the nanosilica with the substrate will improve the durability of the treatment against the penetration of aggressive agents (Fajardo, 2015).
Different application methods have been proposed in the literature, such as soaking the sample into the nanosilica dispersion (Hou, 2015) or by migrating the colloidal nanosilica through the concrete pores under the action of an electric field (Sánchez, 2014). Colloidal nanosilica dispersions have been recently proposed also, for sealing cracks in hardened cementitious materials (Sánchez, 2018). The nanosilica dispersion is a liquid able to penetrate in depth through the crack, and after, the colloidal nanoparticles form a gel-like polymer based on silica, able to seal the crack.
In the present work different results related to the durability parameters of different mortar samples after external repair treatments based on colloidal nanosilica application are shown, both used as surface treatments and as crack sealing treatments. The resistance against water penetration of the treated sample is shown. SEM analysis confirming the presence of the nanosilica inside the cementitious matrix and/or filling the cracks are also included.
2. Materials and methods
Mortar samples prepared with OPC cement in a water/cement ratio of 0,5 have been used for the study. The commercial colloidal nanosilica dispersion Bindzil CC301 (Dp 7 nm, TS: 30%) has been used.
Two different situations have been considered: (a) Surface treatment based on applying the nanosilica dispersion on the sample surface, allowing the penetration through the concrete pores, (b) Injection of a crack with the nanosilica dispersion for sealing the crack.
Durability studies based on estimating the improving on the water absorption capillary penetration have been carried out. The presence of the nanosilica inside the cementitious matrix and inside the c r a c k has been analyzed by SEM.
3. Results and conclusions.
In figure 1 the water capillary absorption tests for a mortar sample with a surface treatment by nanosilica a p p l i c a t i o n penetration (Figure 1-Left) and for a mortar sample with a crack sealed with nanosilica (Figure 1-Right) are shown. A clear decrease on the water capillary absorption
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New Trends in Green Construction