Faturíková, Katarína

Lukáč, Anton

Marčeková, Lýdie

Plško, Alfonz

English

DSpace at VSB Technical University of Ostrava

Sborník vědeckých prací Vysoké školy báňské - Technické umverz1 číslo I, rok 2008, (9�ník U, ř�da hutni9�á článek č. 1397 IMPEDANCE BEHA VIOUR OF HARD�NED CEMENT PASTÉ K. FATURÍK0VÁ 1*,A. PLŠK0 1 , L. MARČEKOyÁ 1 , A. LUKÁČ1 1 •»epartment of Cltemistry and Tec/1110/ogy of Tnorganic Materials, Fac11lty of Tndustrial Tec/1110/ogies, TnUAD, T. Krasku 1809/34, 020 01 PIÍcftov, Sfovak Rep11bfic,faturikova@fpl.tnuni.sk ABSTRACT: The microstructure of hardened cement paste was investigated by A.C. impedance spectroscopy in range of 50 Hz to I MHz. We monitor.the hardening process of cement paste with two different water - ceme.nt ratios (0.4 and 0.5). The results demonstrate that impedance measurement is very sensitive to changes in hydration kinetics and mi�rostructure development due to water - cement ratios. ,KEY WQRD�: cement paste, impedance spectroscopy, microstructure 1. INTRODUCTIONPortland cement is the most common type of cement in general usage in many parts of the world, as it is a basic ingredient of concrete and mortar. It is a fine powder produced by grjnding Portland cement clinker and gypsum which controls the set tiine. When w�ter is mixed with Portland cement, the product - cement paste sets in few hours and hard.ens over a period of weeks. These processes can vary widely depending upon the mix used and the conditions of curing of the product. The reaction and the reaction products are referred to as hydration and hydrates or hydrate phases, respectively. Setting and hardening are 9au�e1 by the formation of a micro�tructure of hydration products of varying rigidity which fills the water-filled interstitial spaces between the solid particles of the cement p��te or mortar. The behaviqr with time of the setting and hardening therefore depends to a very great extent on the size of the int_erstitial spaces, i.e. on the water/cement ratio. After initi.,11 mixing, the water originally between the cement particles gradually becotnes a highly conductive pore fluid, due to t�� dissolution of calcium and alkali ions from cement. The main product of reaction is a poorly crystalline or amorphous calciu·m silicate hydrate commonly referred to as C-S-H (standard cement chemistry notation: C = Ca0, S = Si02, H = H20), with the hyphens denoting a varying C/S ratio non-stoichiometric compound. This phase is also conductive, bec�use its nanometer-sized pores are filled with conductive pore fluid. Another important product is calcium hydroxide, CH, which forms in crystals. With respect to electrical properties, the only phases of importance are capillary porosiťy and C-S-H. 0ther phases are insulators. [I] Since its initial application a� a11 investigative technique for monitoring hydratin& cementitious systems, impedance spectroscopy (IS) is now receiving considerable attentiori as a potentially powerful method in characterizing microstructural evolution and pore strucr,ire development in cement. (2] In IS measurements are made over a range of frequencies and usually presented in a Nyquist plot, showing the imaginary versus r�al components of the ,ii;npedance, with generally takes the form of two complete or partial semi-circular arcs. The low-frequency are is dominated by the pol�rizatión resistance of the eler,trodes,_ �nd the high-frequency are by the behavior of th() bulk material. [3] Impedance �pectra of c_en:ient pa�tes depend_ strongly on the ai:n�unt of porosity present inmicrostructure, and their changes that accompany hydratton are d�te to changmg amounts, distdbution, and arrangements o f m icrostructural phases. [I] . . 221 

Impedance behaviour of hardened cement paste

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Impedance behaviour of hardened cement paste

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