Consolidating treatment of carbonatic rocks by using diammonium hydrogen phosphate (DAHP): influence of application techniques on the penetration depth

Trabajo presentado en el 5th YOuth in COnservation of CUltural Heritage, celebrado en Madrid (España) del 21 al 23 de septiembre de 2016The diammonium hydrogen phosphate (DAHP) has been recently proposed as an inorganic consolidant to favor the formation of calcium phosphates, mainly hydroxyapatite (HAP), (Sassoni et al., 2011). The objective is to obtain a stone consolidating material suitable to restore the decayed carbonate rocks, making up the building structures of historicalarchitectural interest. A fundamental parameter, for assessing the effectiveness of the consolidating treatments, is the penetration depth of the newly-formed strengthening mineral phases, at present not fully under control. According to Franzoni et al. (2015), the methodologies and techniques of application of the consolidant products, as well as the operating conditions, all can play a fundamental role on the outcomes of treatments. For making a contribution to solve this difficult task, this paper is focused on a systematic experimentation based on the application of aqueous solution DAHP on two different carbonatic lithotypes. Tests were carried out on carbonate lithotypes: Carrara marble (Marmo Statuario Michelangelo) and to a biomicritic limestone, collected in Tuscany and central Sardinia (Santa Caterina di Pittinuri), respectively. These lithotypes are generally greatly affected by alteration phenomena, essentially due to their typical microstructure. Indeed, to different lithotypes correspond different porosity features which can affect, in different way and intensity, the vulnerability and durability of the rocks submitted to the decay weathering agents. The aqueous solution DAHP was applied on the stone, using three different methodological techniques, for different times: immersion, brushing and poultice. The assessment of the results, in terms of penetration depth, were carried out by mappings acquired using the Scanning Electron Microscope (SEM). For both lithologies studied, the greatest penetration depth was achieved with the use of poultice: the presence of calcium phosphates was detected up to 5 mm in marble and up to 10 mm in limestone.Research funded by Geomateriales 2 (S2013/MIT-2914) and by Erasmus+ Placedoc (A.A. 2014/15).Peer reviewe