NATURAL AND CALCINED CLAYEY DIATOMITE AS CEMENT REPLACEMENT MATERIALS: MICROSTRUCTURE AND PORE STRUCTURE STUDY

Abstract

This manuscript introduces clayey diatomite from Jelsovec deposit in Slovakia intended for use in cement and concrete industry. Jelsovec deposit contains 3350 kilotons of clayey diatomite to be easily mined. Natural clayey diatomite (CD) and calcined clayey diatomite (CCD) were used to substitute 5 to 15 % by wt. of CEM I according to EN 197-1 Standard. CCD was prepared from CD by calcination at 900 °C for 1 hour. Frattini test was applied for the estimations of pozzolanic activity. Pozzolanic activity of CCD is found to be comparable to that of traditional natural and industrial pozzolans. The pozzolanic activity of the CD is only slightly lower opposite to that of CCD. Both clayey diatomites are behaving as high-efficient pozzolans when partially substituting the Portland cement. Cement composites of Water/Solid ratio of 0.5 with a substitution rate of CEM I between 5 and 15 wt. % CD and CCD were used for the tests. The specimens were studied by X-ray diffraction and thermal analysis as well as mercury intrusion porosimetry after 28- and 365-days test on compressive strength. The composites consumed a larger amount of Ca(OH)2. They had a higher volume of gel-like hydrate phase and finer pore structure relative to the reference cement paste. The present findings indicate that Slovak diatomite from Jelsovec can be considered as a suitable pozzolan for use in cement-based materials. The results show that the microstructural properties of the respective materials are comparable to those of the traditional natural and industrial cement modifiers. Moreover, the substitution of CEM I by CD and CCD save energy and protect the environment by reducing the CO2 emissions.