Vpliv alkalij na mikrostrukturo belitno- sulfoaluminatnih klinkerjev

Čeplak, Barbara (author), Dolenec, Sabina (mentor), Vrabec, Mirijam (co-mentor)

Sintetizirali smo cementni klinker z naslednjimi deleži faz: 60 mas. % C2S (belit), 20 mas. % C4A3Ś (kalcijev sulfoaluminat), 10 mas. % C4AF (ferit) in 10 mas. % CŚ (kalcijev sulfat). Mešanici za klinker smo dodali dve vrsti alkalij (K2O in Na2O) v treh različnih deležih (0,5, 1 oz. 2 mas. %). Proučevali smo vpliv alkalij na tvorbo glavnih in manj zastopanih faz, nadomeščanje ionov in vpliv na mikrostrukturo ter reaktivnost klinkerja. Ugotovili smo, da se količina C2S in C4AF z dodajanjem alkalij povečuje, zmanjšuje pa se količina C4A3Ś in CŚ. V vzorcih z dodatkom alkalij pride do tvorbe manj zastopanih faz: trikalcijevega aluminata (C3A), arkanita (KŚ) in Ca-langbeinita (KC2Ś3), opazili smo nadomeščanje ionov tako z alkalijskimi kationi kot tudi z nekaterimi drugimi ioni (Ca2+, Al3+, Fe3+, S2-, S6+, Si4+). Nadalje, alkalije vplivajo na velikost in obliko glavnih faz belitno-sulfoaluminatnega klinkerja. Večja količina alkalij na splošno zmanjša zrna C2S in C4AF ter poveča zrna C4A3Ś. Zrna C2S so v referenčnem vzorcu sferična, v vzorcih z dodatkom alkalij pa so subhedralna in anhedralna. Zrna C4A3Ś so v referenčnem vzorcu evhedralna, v vzorcih z manjšo količino alkalij tudi heksagonalna, medtem ko so v vzorcih z večjo količino alkalij subhedralna in sferične oblike. Zrna C4AF so v referenčnem vzorcu in vzorcih z manjšo količino alkalij evhedralna in večinoma paličasto oblikovana. Z večanjem količine alkalij pa postanejo čedalje bolj subhedralna. Na velikost in obliko zrn C4A3Ś in C4AF močno vpliva razmerje Al/Fe, določeno v teh dveh fazah. Alkalije uravnavajo tudi hitrost hidratacije. Najbolj reaktiven je vzorec z dodanima 2 mas. % K2O, najpočasneje pa reagira vzorec z enako količino Na2O. Na hitrost hidratacije poleg količine glavnih faz za klinker vpliva še prisotnost manj zastopanih faz (C3A, KŚ in KC2Ś3), poroznost klinkerja ter razmerje posameznih elementov v glavnih fazah.

• Language: Slovenian
• Keywords: belitno-sulfoaluminatni klinker, mikrostruktura klinkerja, alkalije, XRD, SEM/EDS, reaktivnost
• Work type: Master's thesis/paper
• Organization: NTF - Faculty of Natural Sciences and Engineering
• Year: 2020
• PID: 20.500.12556/RUL-124043
• COBISS.SI-ID: 49022979
• Publication date in RUL: 22.12.2020

Secondary language

• Language: English
• Title: Influence of alkalis on microstructure of belite - sulfoaluminate clinkers

Abstract

The cement clinker with the following phase composition: 60 wt.% C2S (belite), 20 wt.% C4A3Ś (calcium sulfoaluminate), 10 wt.% C4AF (feritte) and 10 wt.% CŚ (anhydrite) was synthesized. Two types of alkali (K2O and Na2O) were added to this clinker mixture in three different proportions (0,5, 1 oz. 2 wt.%). The main aim of this work was to determine the influence of the alkalis on the formation of main and minor phases, the ion substitutions and the influence on the microstructure and hydration rate of the clinker. It was found that the amount of C2S and C4AF increases with the addition of alkalis, while the amount of C4A3Ś and CŚ decreases. In addition, minor phases such as C3A (tricalcium aluminate), KŚ (arcanite) and KC2Ś3 (Ca-langbeinite) are formed in the samples with added alkalis. Furthermore, the ions were substituted by alkali cations and by some other ions (Ca2+, Al3+, Fe3+, S2-, S6+, Si4+). Alkalis also influence the size and shape of the main phases of belite-sulfoaluminate clinker. A higher amount of alkali generally reduces the C2S and C4AF grains and increases the C4A3Ś grains. In the reference sample, the C2S grains have a spherical shape, whereas in the alkali-added samples, subhedral and anhedral grains predominate. C4A3Ś grains are euhedral in reference sample and hexagonal in lower alkali samples, while subhedral and spherical grains predominate in the higher alkali samples. C4AF grains are euhedral in both the reference and lower alkali samples. These grains are usually long prismatic. With increasing alkali content they become subhedral. The size and shape of the C4A3Ś and C4AF grains are strongly influenced by the Al/Fe ratio. Alkalis also influence the hydration rate. The sample with the addition of 2 wt% K2O is most reactive, but the sample with the same amount of Na2O is the least reactive. The hydration rate is influenced not only by the number of main phases for clinker, but also by the presence of minor constituents (C3A, KŚ, KC2Ś3), the porosity of the clinker and the ratio of individual elements in the main phases.

• Keywords: belite-sulfoaluminate clinker, microstructure of clinker, alkalis, XRD, SEM/EDS, reactivity