ADVANCED MINERALOGICAL AND CRYSTALLOGRAPHICAL TECHNIQUES FOR UNDERSTANDING TRANSFORMATION PROCESSES IN NATURAL MATERIALS AND THEIR SYNTHETIC ANALOGOUS

This study aims to compare the Combustion Pyrometamorphism (CP) process involving limestone and marly-limestone belonging to Hatrurim Basin in Israel and the human-made cement manufacture by means of both standard (Reflected and Transmitted Light Microscopy, X-ray Fluorescence, Laboratory X-ray Powder Diffraction, Laboratory Single Crystal X-Ray Diffraction, Electron MicroProbe Analyser, Scanning Electron Microprobe, Calorimetry) and innovative analytical techniques (Micro X-ray Computed Tomography, Synchrotron X-ray Powder Diffraction with in-situ and ex-situ experiments and Neutron Diffraction), highlighting differences and similarities between natural and synthetic process useful to better understand the geological process and improving cement manufacture. CP is considered as a complex geological process involving sedimentary sequences in two main stages: (i) 1st stage of High Temperature (HT) (850 – 1650 °C) and Low Pressure (LP) (< 1 km) metamorphism due to the self-ignition of coal seams or methane-rich hydrocarbon gases coming from depth reservoirs; (ii) 2nd stage of LT (< 300 °C) and LP metamorphism in which takes place fluids and gas interactions with previous combusted rocks. Rocks resulting from this multistage process have similar texture, mineral assemblage and chemical composition to several synthetic human-made materials, such as metal-slags, ceramics, anhydrous and hydrated cements. CP is a LP and HT process, representing an uncommon field for petrological studies and metamorphosed rocks: there is a lack of geological and petrological information in the field of extremely HT and LP metamorphism especially for marls and limestone, increasing the difficulties to better explain CP process. Cement represents the most important building materials used for all constructions ranging from ordinary urban planning (civil houses, road foundations, etc.) to strategical buildings (dams, tunnels, bridges, underground nuclear waste repositories, skyscrapers foundations, etc.). It is obtained by heating at HT a fine mixture of limestone and clay in a rotary kiln. Nowadays, cement manufacture represents the 3rd anthropogenic CO2 emission source due to the high CO2 emission during the decomposition of limestone. Therefore, many efforts have been made over last decades trying to reduce the greenhouse gases footprint of cement manufacture by designing green-cements, such as Calcium SulfoAluminate Cements (CSA) and Belite Cements (BC), that use alternative and less CO2 releasing raw materials with lower thermal treatment. To cope with the aim this project was organised in three main parts: (i) study of rock samples of natural cements (larnite-rich rocks) and their protolith (impure limestones) collected in Israel in Hatrurim Basin region; (ii) laboratory scale production of two different green-cements, High Ferrite Belite Cement S-doped (HFBC S-doped) and Cement S-P-F-doped were laboratory prepared starting with an industrial raw meal and previous collected Israeli limestone, respectively; (iii) hydration properties comparison between HFBC S-doped and natural anhydrous cement (larnite-rich rocks). The investigation and comparison with conventional and innovative techniques of natural CP rocks and human-made synthetic equivalents led important information useful for both geological and industrial purposes: (i) better understanding on HT and LP metamorphism of limestone, hence clarifying processes occurring during CP (metamorphic reactions, melting points, highest T reached, microtextural changes, etc.); (ii) predicting the evolution of cement-based materials on long-term hydration (t > 1000 years), crucial for repository of low-emission nuclear waste and strategical buildings (dams, tunnels, bridges, building foundations, etc.); (iii) designing new green-cements for reducing cement manufacture CO2 footprint and waste management by studying the effects of simultaneous dopants (F, P and S), different thermal treatments and raw materials particle size.