In-situ and laboratory Raman spectroscopic analysis on beachrock deposits: Characterisation of the trapped materials

Raman spectroscopy, including in-situ and laboratory analyses, were carried out in beachrock outcrops located in temperate latitude (Arrigunaga beach, Bilbao Estuary, North of Spain) to characterise the wide variety of sediments and wastes trapped within the cements. In the examined beachrocks (coastal sedimentary structures formed in the intertidal zone through the early precipitation of carbonates) the presence of abundant slag and anthropogenic wastes is noticeable. In-situ Raman analysis revealed the presence of cristobalite (SiO2), tephroite (Mn2SiO4), quartz (SiO2), rhodonite (MnSiO3), labradorite (Ca,Na)(Si,Al)(4)O-8, hematite (-Fe2O3), gypsum (CaSO(4)2H(2)O) and amorphous carbon (C) as the main constituents in the trapped materials. Those were also identified off site together with other phases such as limonite (FeO(OH)nH(2)O), lepidocrocite (-FeOOH), arsenopyrite (FeAsS), fayalite (Fe2SiO4) and anatase (TiO2). As secondary compounds, portlandite (Ca(OH)(2)), C-S-H (Ca(3)Si(2)O(7)3H(2)O), gypsum and possibly ettringite (3CaOAl(2)O(3)3CaSO(4)32H(2)O) were identified only in-situ, and a possible evolution to the more stable thaumasite (3CaOSiO(2)CO(2)SO(3)15H(2)O) was found in the laboratory analyses. Therefore, the applied methodology and specifically the in-situ Raman spectroscopy analyses resulted particularly valuable, allowing an accurate description of the trapped materials and the compounds formed by hydration and/or sulphate attack (probably from the high level of atmospheric aerosols coming from seawater or industrial activity nearby), giving an insight of the complexity of the examined outcrops. Copyright (c) 2015 John Wiley & Sons, Ltd.