Page 147 - New Trends in Green Construction

IMPROVING THE BIOCIDAL PROPERTIES OF THE RESTORATION MORTARS BY CARBENDAZIM ADSORBED ON INORGANIC SUBSTRATES
Adrián Pastor, Manuel Cruz-Yusta, Ivana Pavlovic, Luis Sánchez
Keywords: biocide, mortar, layered double hydroxide, clay, carbendazim 1. Introduction
The high microbial contamination of the stone materials present in the urban heritage provokes a negative effect on the aesthetics and durability of these materials, sometimes compromising the integrity of certain constructions (De Muynck, 2009). Currently, the most common prevention systems to avoid colonization are based on the use of biocides. However, the durability of the antimicrobial effect of the material is greatly reduced over time. In this sense, this research focuses on compounds that can protect biocides from external agents and thus improve the durability of stone material (Scarfato, 2016).
Layered Double Hydroxides (LDH) are materials similar to brucite. They are formed by positive sheets whose charge is balanced with the anions existing in the interlayer space. On the other hand, the clays have an antagonistic structure, in which the interlayer cations compensate the negative charge of the sheets.
In the present work, the adsorption of the biocide carbendazim (CBZ) in a layered double hydroxide and different clays has been studied. The adsorption complexes with the best biocidal activity were incorporated into a lime-based mortar.
2. Materials y methods
For the CBZ adsorption study, the adsorbent was added to a solution of CBZ. The mixtures were shaken to reach equilibrium and they were subsequently centrifuged. On the one hand, the CBZ concentration of the supernatant was measured by UV-HPLC. On the other hand, the solid (adsorption complex) was dried in an oven (70oC) and tested for biocidal activity. The commercial clays used as adsorbents were: SWy-1, Cloisite 10 (CL10) and Cloisite 20 (CL20). The LDH adsorbent was synthesized (LDH-DDS), the interlayer anion being dodecyl sulfate.
The biocidal activity of the samples was investigated. For this purpose, the adsorption complexes were placed in a Petri dish containing an inoculated strain of algae (Stichococcus Bacillaris) or fungus (Aspergilius Niger). At the end of the incubation period, the biocidal properties of the samples were visually analyzed by the presence or absence of microorganisms.
The adsorption complexes with the better biocidal properties were incorporated to the formulation of a hydraulic lime-based mortar. The mortar mix (mixing water = 19%) was placed in silicone molds (h = 5 mm). After a week, the samples were demolded and were left to cure for 21 days (20 ± 2 °C and 65 ± 5% relative humidity). Finally, the biocidal activity of the mortars was evaluated once, before and after, they were subjected to a standardized leaching test (EA NEN 7375: 2004).
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