Studij utjecaja amorfnog SiO2 na ranu fazu hidratacije i stabilnost cementnog kamena : doktorska disertacija - Zelić, Jelica; Krstulović, Ruža; Tkalčec, Emilija; Krolo, Petar, kemičar; Mitrović-Kessler, Edita; Krstulović, Ruža (Split : J. Zelić, 1997)
Sažetak: Istraživan je utjecaj amorfnog SiO2 (SiO2 prašina, "silica fume") dobivenog iz filterskog postrojenja u proizvodnji ferocilicija, kao pucolanskog dodatka cementima, na ranu hidrataciju industrijskog cementa, te na fizičko-mehanička svojstva i kemijsku otpornost cementnog kamena. Za provedbu ispitivanja uporabljeni su uzorci: alit (C3S), miješani portland-cement oznake PC 30t 45s, Sulfatnootporni portland-cement oznake SPC-45 kao referentni uzorak, te amorfni SiO2 ("silica fume") kao zamjenski dodatak u cementu. Praćenje hidratacijskog procesa provedeno je na uzorcima cementa paste s različitim masenim udjelom amorfnog SiO2 (2-15%).
Proces je praćen preko točno definiranih komponenata čije su promjene tijekom hidratacije ispitivane kemijskim (gubitak žarenjem), termičkim (TG/DTG, DSC) i elektrokemijskim (električna provodnost razrijeđenioh suspenzija) metodama. Određivanjem kemijski vezane vode za Ca(OH)2 i za hidraulične CSH faze, te kinetičkom analizom termičke razgradnje Ca(OH)2 nastalog hidratacijom, dobiveni su rezultati koji su poslužili za matematičku obradu i izračunavanje stupnja hidratacije, odnosno stupnja termičke razgradnje Ca(OH)2 kao pokazatelja napredovanja hidratacijskog procesa u određenim reakcijskim sustavima. Iz eksperimentalnih podataka stupanj hidratacije ([alfa]) - vrijeme (t) provedena je kinetička analiza razvoja hidratacije po pojedinim metodama.
Analiza je provedena na predodžbi odvijanja reakcija po metodi Šestakova, Bezjak-Jelinić i Hu Rongzu-a i sur. uz pprogramsku podršku na računalu. Kod razvoja i testiranja modela korišten je matematički programski paket MATHCAD za svaku metodu. Za svaki kinetički model datisu zaključci o njegovoj valjanosti i značenju za primjenu kvantitativnme ocjene procesai mehanizma hidratacije. Od primjenjenih metoda najsveobuhvatniji se pokazao Bezjak-Jelenić model. Njime se mogu različiti pojedini vremenski razmaci u kojima se odvijaju pojedini periodi procesa hidratacije od nukleacije i rasta prvih produkata (period produkcije) preko interakcije na granici faza (period ubrzanja) do procesa difuzije.
Model prema Hu Rongzu i sur. je veoma sofisticirana metoda kojom se pomoću DSC analize određuje mogući mehanizam reakcije uz istovremeno određivanje kinetičkih parametara: energije aktivacije (E), predeksponencijalnog faktora (A), te reda reakcije. U radu je ova metoda dalje razvojena i usavršena uvođenjem novih kriterija za ocjenu dobrote slaganja teorijskih jednadžbi s eksperimentalnim podacima. Ustvrđivanje utjecaja amorfnog SiO2 kao pucolanskog dodatka u sustavu cement-voda provedeno je pomoću različitih metoda ocjene i kvantificiranja njegove pucolanske aktivnosti uvođenjem odnosa brzina odvijajućih reakcija hidratacije i pucolanske reakcije, te pomoću bilance mase Ca(OH)2 koji se razvije tijekom hidratacije u uzorcima bez i s dodatkom amorfnog SiO2. Rezultati ukazuju da je pucolanska reakcija uočljiva poslije 72 sata hidratcije.
Na temelju uzajamnih vrijednosti vezanih uz fizičko-mehaničke osobine cementnih mortova (Čvrstoća, pozornost, raspodjela pora) date su matematičke ovisnosti promjena osobina cementnog morta o dodatku amorfnog SiO2. Najbolje osobine pokazuje mort u kojem je 8 mas. % cementa zamijenjeno istim udjelom amorfnog SiO2. Poroznost je uzorcima morta određena živim porozimetrom, a za karakterizaciju raspodjele veličine pora korištena je RRSB-funkcija. Knudsen-ovom relacijom istražena je funkcionalna ovisnost čvrstpće o vremenu hidratacije. Veza između stupnja hidratacije i odgovarajuće čvrstoće uspostavljena je preko vremenske varijable. Ovisnost stupnja hidratacije ([alfa]) - čvrstoća ukazuje na paraboličnu matematičku zakonitost.
Ovim postupkom istraživanja razvoja hidrtacijskog procesa može se povezati i objasniti rane faze hidrtacije na osobine potpuno očvrslog cementnog kamena (morta) i ustvditi kompatibilnost ispitivanih metoda. Na osnovu dobivenih rezultata otpornosti uzoraka morta s različitim dodatkom amorfnog SiO2 u otopinama Na- i Mg-sulfata, ustvrđeno je da su uzorci s većimdodatkom amorfnog SiO2 (iznad 5 mas. %) otporniji prema koroziji od referentnog uzorka morta na bazi sulfatnootpornog cementa. Ispitivanjima je također dokazano da stabilnost uzorka znatno ovisi o načinu njegove prethodne priprave i početnog razvoja procesa hidratacije. Značajnu ulogu ima poroznost cementnog kamena i raspodjela pora koje su funkcija masenog udjela dodatka amorfnog SiO2. Pokazalo se da najpovoljniji stupanj polidisperznosti pora ima uzorak s 8 mas. % amorfnog SiO2.
Ovaj uzorak ima najveću čvrstoću i pokazuje njabilju stabilnost prema koroziji bez obzira na tip sulfatne otopine. Prikazanim kompleksnim ispitivanjima moguće je na osnovu praćenja promjena parametara tijekom rane hidratacije cementa uočiti i sagledati slijed događaja na konačna vremena hidratacije, kao i bolje kvantificiranje mehaničkih osobina i stabilnosti cementnog kamena. Ključne riječi: Amorfni SiO2, pucolanska aktivnost, proces hidratacije, kinetička analiza, matematički model, diferencijalna pretražna kalorimetrija, termogravimetrija, portland-cementni mort, razvoj čvrstoća, faktor djelotvornosti pucolana, poroznost i raspodjela veličine pora, sulfatna korozija, bubrenje, modul elastičnosti, stabilnost, trajnost
Abstract: The effect that amorphous SiO2 (SiO2 dust, silicia fume) obtained from filters in production of ferrosilicon and used as a pozzolanic addition to cements, has on early stages of industrial cement hidration and on physical and machanical properties and chemicalresistance of the cement stone has been examined. The following samples were used in examinations: alite (C3S), blended Pertland blastfurnace cement marked PC 30t 45s, sulphate-resistant Portland cement marked SPC-45 as the referent sample, and amorphous SiO2 (silica fume) as the substitute addition in cement. Hydration processes were examined in cement paste samples containing different mass portions of amorphos SiO2 (2-15 mass %).
The process was monitored through precisly defined components whose changes during hydration were determined by means of chemical (loss on ignition), thermal (TG/DTG, DSC), and electrochemical(electrical conductivity of diluted suspensions) methods. By determining water chemically bound to Ca(OH)2 and to hydraulic CSH phases, and by a kinetic analysisof thermal decomposition of Ca(OH)2 formed during hydration, results were obtaind which served as a basis for mathematical processing and calculation of the hydration degree, i.e. the degree of thermal decomposition of Ca(OH)2 as an indicator of theextent to which the hydration process has developed in specific raction systems. Based on the experimental data on the hydration degree ([alpha]) - time (t), kinetic analyses of hydration were carried out according to various methods.
Analyses were carried out according to the conception of reaction development in the methods by Šestakov, Bezjak-Jelenić and Hu Rongzu et al., with computer software support. The mathematical program package MATHCAD was used in development and testing of the models for each of methods. Conclusion were reached about validity of eachof the konetic models and their applicability in quantitative evaluation of the hydration process and mechanism. Of all the methods appled, the most comprehensive proved to be the Bezjak-Jelenić model. It can serve to distinguish individual intervals in which individual periods of the hydration process take place, from nucleation and growth of the first products (the induction period) through interactions at phase boundaries (the accelaration period) to the diffusion process.
The model according to Hu Rongzu et. al.is a very sophisticated method which uses the DSC analysis to determine the possible reaction mechanism whith simultaneous determination of kinetc parametrs: the activation energy (E), the pre-eksponential factor (A) and the reaction order. This method has been further developed in this work by introducing new ciriteria for evaluation of the correspondence of theoretical equations and experimental data. The effect of amorphous SiO2 as the pozzolanic addition in the cement - water system was determined by means of different methods of evaluation and quantification of its pozzolanic activity by introducing the ratio of the hydration reaction rate to the pozzolanic rate, and by means of the balance of the mass of Ca(OH)2 developed during hydration in samples with and without amorphous SiO2.
The results indicate that the pozzolanic reaction is evident after 72 hours of hydration. Correlations with physical and mechanical properties of cement mortars (strength, porosity, pore size distribution) provided a basis for mathematical expression of dependence of changes in cement stone properties on addition of amorphous SiO2. The best properties were encountered in the mortar were 8 mass % of cement had been substituted by the same mass of amorphous SiO2. Porosity in mortar samples was determined by mercury porosimeter, and RRSB function was used to determine the pore size distribution. Knudsen's relation was used to examine the functional dependence of streight on hydration duration. The relation between the hydration degree and the corresponding strenght was established by means of the time varisble.
The hydration degree ([Alpha]) - strenght dependence indicates a parabolic mathematical function. This process of examinantin of the hydration process development can explain the effect of the early stages of hydrtaion on properties of fully hardened cement stone (mortar) and determine compatibility of methods examined. The results obtained for mortar samples with different additions of amorphous SiO2 in solutin of Na- and Mg-sulphates indicated that samples with higher quantities of amorphous SiO2 (more than 5 mass%) showed better resistance to suplhate to attack than the referent mortar based of the sulphate-resistant cement. The examinations also proved that sample stability was greatly by the method of its previous preparation and initial development of the hydration process.
An important role was played by porosyti of the cement stone and pore size distributin which were dependent on the mass portion of the amorphous SiO2 addition. The best degree of pore poly-despersion was encountered in the sample with 8 mass % of amorphous SiO2. This sample had the highest strength and displeyed best stability towards suplhate attack regardless of the type of sulphate solution. The complex examinations presented make it possible to observe and envisage the sequence of events in the final hydration time, as well as to quality mechanical poroperties and stability of the cement stone, based on monitoring the changes in the pparameters during the early stages of cement hydration.
Key words Silicia fume, pozzolanic activity, hydretion process, kinetic analysis, mathematical modelling, differential scanning calorimetry - DSC, thermogravimetric, Portland cement mortars, strenght development, pozzolanic effectiveness ratio, porosity and pore size distribution, corrosion of sulphate attack, expansion, elastic modudlus, stability, durability
Doktor tehničkih znanosti - kemijsko inženjerstvo
Mentor: Ruža Krstulović; Komisija za ocjenu: Emilija Tkalčec, Petar Krolo, Edita Mitrović-Kessler, Ruža Krstulović; Komisija za obranu: Emilija Tkalčec, Petar Krolo, Edita Mitrović-Kessler, Ruža Krstanović; datum obrane: 26.05.1997.; datum promocije
Sveučilište u Splitu, Tehnološki fakultet u Splitu, Split, 1997
Bibliografija: str. 172-182
Sažetak
Keywords: Cement -- Hidratacija; Cementni kamen -- Stabilnost