ABSTRACT
Alteration of basaltic glass and in situ mineral growth are fundamental processes that influence the chemical and material properties of Earth's oceanic crust. These processes have evolved at the basaltic island of Surtsey (SW Iceland) since eruptions terminated in 1967. Here, subaerial and submarine lapilli tuff samples from a 192 m-deep borehole drilled in 2017 (SE-02b) are characterized through petrographic studies, X-ray powder diffraction analyses, and SEM-EDS imaging and chemical analyses. The integrated results reveal (i) multi-stage palagonitization processes in basaltic glass and precipitation of secondary minerals from matrix pore fluids, (ii) multi-stage crystallization of secondary phillipsite, analcime and Al-tobermorite in the vesicles of basaltic pyroclasts and (iii) variations in palagonitization processes as a function of thermal and hydrological domains. Although temperature appears to be an important factor in controlling rates of secondary mineralization, the chemistry of original basaltic components and interstitial fluids also influences reaction pathways in the young pyroclastic deposits. The integration of systematic mineralogical analyses of the 50-year-old tuff from one of the most carefully monitored volcanic sites on Earth, together with temperature monitoring in boreholes since 1980, provide a reference framework for evaluating mineralogical evolution in other Surtseyan-type volcanoes worldwide.
ABSTRACT
This research has focused on the assessment of the compositional features and mechanical and antifouling performances of two different mortars formulated for an underwater setting, and which contain Mg(OH)2 as an antifouling agent. Regarding the mechanical characterization, the uniaxial compressive strength and flexural strength were measured. The composition of the materials was explored by differential thermal/thermogravimetric analysis (DTA-TG), X-ray diffraction analysis (XRPD), and scanning electronic microscopy (SEM) coupled with EDS microanalysis. The assessment of the biological colonization was evaluated with colorimetric analysis and image analysis. The results suggest that both mortars have good mechanical resistance once set underwater. Moreover, the adding of Mg(OH)2 improves the resistance toward biofouling; this was observed both in laboratory and sea-exposed specimens.
ABSTRACT
The present paper assesses petrographic, mineralogical, chemical, and technological features of different zeolitic tuff samples from various western USA districts of the Basin and Range Province containing mainly erionite, mordenite, clinoptilolite/heulandite and phillipsite. The aim of this characterization is to evaluate the pozzolanic activity of these samples according to European normative UNI-EN 196/5 (Fratini test) to program a possible use as addition for blended cements. Petrographic and mineralogical results show that the two phillipsite-bearing tuffs have a higher theoretical Cation Exchange Capacity (CEC) than the other samples; technological characterization shows a pozzolanic behavior for all the samples but higher for the tuff samples containing phillipsite, which shows a higher reactivity with CaO. All the samples could be thus advantageously employed for the preparation of blended cements, potentially reducing CO2 emissions by 70-90%.
