Neposredne dinamične strukturno-kemijske preiskave kinetičnih procesov hidratacije belita

Barber, Polona (author), Vrabec, Mirijam (mentor), Šturm, Sašo (co-mentor)

V zadnjih letih zaradi okoljevarstvenih razlogov močno narašča zanimanje za cemente bogate z belitom. Ker reakcije in procesi hidratacije belita še vedno niso dobro poznani, sem se v magistrskem delu osredotočila na preučevanje reakcije hidratacije belita. Na vzorcih, ki so jih sestavljali 20 nm - 2 μm veliki delci sintranega belita, smo izvedli osnovno karakterizacijo materiala z metodo rentgenske praškovne difrakcije (XRD), in preučili morfologijo delcev z uporabo vrstične elektronske mikroskopije (SEM) v kombinaciji z energijsko disperzijsko spektroskopijo rentgentskih žarkov (EDS). Reakcijo hidratacije kot funkcije časa sem izvedla pri treh različnih pogojih: pri sobni temperaturi, pri temperaturi 80 °C in pri temperaturi 200 °C. Eksperimente hidratacije sem izvedla v časovnih intervalih od 6 ur do 42 dni. Na hitrost poteka reakcije hidratacije vplivajo oblika in velikost začetnega materiala ter temperatura, in sicer z višanjem temperature narašča tudi hitrost reakcije. Mineraloška sestava vzorcev hidratiziranih pri sobni temperaturi in pri 80 °C se s časom ne spreminja, v vzorcih prevladuje kalcijev silikat hidrat (C-S-H). V vzorcih se pojavi več različnih morfoloških oblik C-S-H, ki so ponekod prisotne istočasno. Velikost delcev C-S-H III, ki je ena izmed morfoloških oblik C-S-H, se s časom tekom reakcije ne spreminja. Temperatura vpliva tudi na velikost delcev C-S-H III, in sicer so delci manjši pri povišani temperaturi. Za nastanek oziroma kristalizacijo kalcijevega hidroksida (CH) je potrebna prenasičenost s Ca2+ in OH- ioni v raztopini. Reakcija hidratacije čistega belita v čisti vodi pri sobni temperaturi brez dodanih aditivov poteka izjemno počasi. Za dosego trdnosti visoko belitnih cementov v sprejemljivem času je torej potrebna uporaba dodatkov in primesi, ki pospešujejo reakcijo hidratacije.

• Language: Slovenian
• Keywords: belit, hidratacija cementa, strukturno-kemijske preiskave, vrstična elektronska mikroskopija, rentgenska praškovna difrakcija
• Work type: Master's thesis/paper
• Organization: NTF - Faculty of Natural Sciences and Engineering
• Year: 2018
• PID: 20.500.12556/RUL-105557
• COBISS.SI-ID: 1452894
• Publication date in RUL: 06.12.2018

Secondary language

• Language: English
• Title: Direct dynamic structural and chemical analysis of belite hydration kinetics

Abstract

Due to environmental issues, interest and usage of high belite cements has increased in the last few years. Since hydration kinetics and reactions of belite are still quite unknown, this master’s thesis investigates and observes these processes. Using an X-ray powder diffraction (XRD), the basic characteristics of 20 nm – 2 μm belite particles were determined. Using a scanning electron microscope (SEM) in combination with energy-dispersive X-ray spectroscopy (EDS), morphology of particles were studied. Reactions of hydration as a function of time were executed at three different temperatures: room temperature, at temperature of 80 °C and at temperature of 200 °C, and at various time intervals ranging from 6 hours to 42 days. Based on SEM observations and XRD results, several findings were derived. The rate of hydration is affected by size and shape of the original starting material. The temperature also has an important impact on the hydration rate; higher temperatures lead to a higher reaction rate. The mineralogical composition of samples hydrated at room temperature and at temperature of 80 °C does not change during 42 days of hydration. The predominate product in all samples is a nearly amorphous calcium silicate hydrate (C-S-H). Many different morphological types of C-S-H can be found in samples, in some samples even simultaneously. Temperature affect the size of C-S-H III particles, the particles mentioned are smaller in samples hydrated at a higher temperature. However, the size of C-S-H III (C-S-H III is one off the morphological shapes of C-S-H) particles does not change during the hydration progress. Crystallization of calcium hydroxide (CH) begins when the solution becomes oversaturated with Ca2+ in OH- ions. Hydration of pure belite in pure water at room temperature without any added additives proceeds very slowly. In order to develop the strength of high belite cements in an acceptable time frame, the application of specific additives and alloys, permitting an increase in the hydration rate is necessary.

• Keywords: belite, cement hydration, structural and chemical analysis, scanning electron microscopy, X-ray powder diffraction