Supervisors info:
Βασιλάτος Χαράλαμπος, Επ. Καθηγητής Τμήμα Γεωλογίας & Γεωπεριβάλλοντος, ΕΚΠΑ (Επιβλέπων),
Γλυκερία, Καθηγήτρια Ε.Μ.Π., Σχολή Χημικών Μηχανικών,
Πομώνης Παναγιώτης, Καθηγητής Τμήμα Γεωλογίας & Γεωπεριβάλλοντος ΕΚΠΑ
Summary:
Natural materials as pozzolanic cement additive have been investigating for several decades. The need for drastic reduction of CO2 pollutants resulted by the clinker production cycle has been intensified and defined by international entities in the frame of the climate crisis. Studies conducted by major cement companies aim at zeroing the environmental footprint of cement production by 2050 according to the targets of the European Cement Organization. That goal seems optimistic due to the alternative solutions have to be established to whole cement production chain. The use of natural pozzolans as cement substantial is considered as an alternative way to reduce drastically CO2 emissions due to non-calcination process which is required for the typical raw materials as limestone and clays. With the progress made so far and supported by the substitution of cement by secondary cementitious materials through which CO2 pollutants are estimated to be reduced by 1.3 gt globally per year. As it is known, many rocks derived from Aegean volcanic activity exhibit pozzolanic properties thus in the research for alternative cementitious materials, the current Aegean volcanic arc and similar rocks from the east-north Aegean region were marked as the study areas. Here, samples belonging to a wide range of geological formations approached as pozzolanic cement additives and relative studies obtained, thus this work discuss the measurement of pozzolanicity of geological formations that have not been sufficiently studied as cement additives but have been relatively evaluated for other industrial uses. Specifically, pumice samples were studied originated from Gyali island, Pleistocene and Pliocene rhyolite of Kefalos in Kos Island, volcanic tuffs of Kefalos and the plateau of Kos Island as well, zeolitic rhyolite of Samos Island and ivy tuffs of Chios Island. The samples presented here, were selected from a series of samples from various formations taken in the field after preliminary evaluation. The methods of the preliminary analyses for the initial and further evaluation of the samples were XRD, XRF, SEM-EDS and Blaine, while the direct method of measuring pozzolanicity concerns the consumption of portlandite from the material tested through modified Chapelle test hydro chemical method. The Chapelle method was selected as a short time alternative method for measuring the pozzolanicity of raw materials and was compared with other methods regardingits correlation to estimate the final compressive strength of a potential pozzolanic cement. The materials can be classified as natural pozzolana as the estimated active silica exceeds 25% as defined in EN 197 1-2 specification, on the contrary the inductive correlation between pozzolanicity and compressive strength was not found to be satisfactory (R2 ῀0.53). The Chappelle method lags behind the calorimetry method regarding the reliability of correlation between portlandite consumtion and final compressive strength prediction. As stated in the literature, it adheres to fewer of the following basic criteria i) the method must be practical and simple in terms of execution and cost ii) provide rapid results iii) be repeatable and reproducible iv) be generally applicable to all cement additives v) allow easy comparisons between results and quality criteria. In the above conclusions, for a deposit context, the use of natural pozzolana of volcanic origin as a substitute of common cement is quite complicated due to their mineralogical and chemical heterogeneity thus the confirmation of deposits quality through the above techniques may overlaying the regular standard methods with specimens for the mechanical strength definition. For their safe use in construction industry, it is necessary to clarify the main issues such as the nature of each natural pozzolan type with respect to its hydration rate followed by the C-S-H structure and furthermore to their mineralogical and chemical homogeneity. In the literature, natural pozzolans of high activity and satisfactory performance are considered to be kaolin either by mechanical or thermal treatment. This work, concludes that perlite formations in Kos Island (Pleistocene and Pliocene rhyolites) are promising materials and could be considered as potential pozzolanic source for the partial Portland clinker subsidiary due to their large-scale homogeneity and specifications compliance according to current study, be introduced either upstream or downstream of the cement production process. Furthermore, the volcanic tuffs of Chios Island and the zeolitic formation of Samos due to their high loss on ignition could be successfully used downstream of the production process to produce a pozzolanic concrete.
Keywords:
Raw materials, cement industry, clinker, pozzolanas, igneous rocks, Chapelle method
