Title Influence of supplementary cementitious materials on durability of calcium aluminate cement under different curing regimes Title (english) Utjecaj mineralnih dodataka na trajnost kalcij aluminatnoga cementa pri različitim temperaturama njegovanja Author Alma-Dina Bašić Mentor Marijana Serdar (mentor)Committee member Ivana Banjad Pečur (predsjednik povjerenstva)Committee member Marijana Serdar (član povjerenstva)Committee member Jason H. Ideker Granter University of Zagreb Defense date and country 2024, Croatia Scientific / art field, TECHNICAL SCIENCES Universal decimal classificationUDC ) 624/625 - Civil and structural engineering. Civil engineering of land transport. Railway engineering. Highway engineering Abstract The cement industry is facing a global problem of environmental pollution during cement production. To reduce the negative impact on the environment, the possibility of using supplementary cementitious materials – SCMs, e.g. industrial by-products or natural materials, as a replacement for part of the cement in concrete has been already investigated for many years. Calcium aluminate cement (CAC) has been used for more than 100 years and is mostly used for special purposes where resistance to aggressive environments is required. However, the application of CAC is limited by the occurrence of the conversion process, which increases the porosity of the cement matrix and reduces its mechanical properties. The use of SCMs as a replacement for part of the CAC could reduce the negative environmental impact of cement production and improve the mechanical properties of concrete, especially when exposed to higher curing temperatures. Previous research has shown that the application of blast furnace slag reduces the impact of the conversion process. However, due to challenges with the availability and cost of slag, there is a need to investigate other possible SCMs. In this dissertation, calcined clay, which is available in the region and has a medium kaolin content, was used. Although the rate of the conversion process is reduced by the use of SCMs, the question of the durability of such binders arises.
In the first phase of this dissertation, the research focused on the influence of slag and calcined clay on the mechanical properties of CAC cement. At the same time, the changes in hydration products and pore structure were analysed under the influence of two different curing regimes (20°C and 38°C). It was found that calcined clay can be used as a replacement for part of the CAC instead of slag to reduce the effects of the conversion process. Furthermore, the results show that the addition of calcined clay to CAC strätlingite is formed, which densifies the structure and inhibits the conversion process.
In the second phase, the research focused on evaluating the durability of concrete based on CAC with and without the addition of slag or calcined clay. The durability assessment included tests on resistance to carbonation, resistance to chloride penetration, resistance to acid attack and sulphate resistance. The tests were carried out on systems before and after the conversion process, whereby the conversion process was accelerated by curing at 38°C. The results show that the addition of slag or calcined clay reduces the resistance of CAC under different environmental conditions. However, while the resistance of systems without SCMs was significantly affected by these influences, the resistance of systems with slag or calcined clay was only slightly affected after the conversion process.
The research conducted in this dissertation shows that slag and calcined clay can be used as a replacement for 30% of CAC. Understanding the effects of slag and clay on microstructural changes, their contribution to mitigating the effects of the conversion process and their effects on durability properties allows for a wider application of CAC-based systems.
Abstract (english) Cementna industrija suočava se s globalnim problemom zagađenja okoliša tijekom proizvodnje cementa. Kako bi se smanjio negativan utjecaj na okoliš, već dugi niz godina istražuje se mogućnost primjene mineralnih dodataka (nusproizvodi industrije ili prirodi materijali) kao zamjena za dio cementa u betonu. Kalcij aluminatni cement koristi se već više od 100 godina, a najčešće se primjenjuje za posebne namjene gdje je potrebna otpornost na agresivni okoliš. Međutim, primjenu CAC cementa ograničava pojava procesa konverzije kojim se povećava poroznost cementne matrice i smanjuju mehanička svojstva. Upotrebom mineralnih dodataka za zamjenu dijela CAC cementa smanjuje se negativni utjecaj proizvodnje cementa na okoliš te se poboljšavaju mehanička svojstva betona pogotovo pri izloženosti povišenim temperaturama prilikom njegovanja. Dosadašnja istraživanja pokazala su da se primjenom zgure visokih peći smanjuje utjecaj procesa konverzije, no zbog izazova s dostupnošću i troškovima zgure, postoji potreba za istraživanjem drugih mogućih mineralnih dodataka. U ovoj disertaciji korištena je kalcinirana glina, koja je dostupna u regiji, sa srednjim sadržajem kaolina. Iako se stopa procesa konverzije smanjuje primjenom mineralnih dodataka, otvara se pitanje trajnosti takvih veziva.
U prvoj fazi ove disertacije istraživanje je usmjereno na utjecaj zgure i kalcinirane gline na mehanička svojstva CAC cementa. Istovremeno su analizirane promjene produkata hidratacije i strukture pora pod utjecajem dva različita režima njegovanja (20°C i 38°C). Utvrđeno je da se kalcinirana glina može koristiti kao zamjena za dio CAC cementa umjesto zgure, za smanjenje utjecaja procesa konverzije. Također, rezultati pokazuju da se dodatkom kalcinirane gline CAC cementu stvara stratlingit koji smanjuje poroznost i inhibira proces konverzije.
U drugoj fazi istraživanje je usmjereno na procjenu trajnosti CAC cementa sa i bez dodatka zgure ili kalcinirane gline. Procjena trajnosti obuhvaća ispitivanja otpornosti na karbonatizaciju, otpornost na prodor klorida, otpornost na djelovanje kiselina te sulfatnu otpornost. Ispitivanja su provedena za sustave u kojima nije bilo procesa konverzije i za sustave u kojima je proces konverzije ubrzan njegovanjem na 38°C. Rezultati pokazuju da dodatak zgure ili kalcinirane gline smanjuje otpornost CAC cementa na razna djelovanja iz okoliša. Međutim, dok je u sustavu bez mineralnih dodataka otpornost na navedena djelovanja značajno narušena nakon konverzije, otpornost sustava sa zgurom ili kalciniranom glinom nije značajno narušena nakon procesa konverzije.
Istraživanje provedeno u ovoj disertaciji pokazuje da se zgura i kalcinirana glina mogu primjenjivati kao zamjena za 30% CAC cementa. Poznavanje utjecaja zgure i gline na promjene u mikrostrukturi, njihov doprinos na suzbijanje utjecaja procesa konverzije te utjecaj na trajnosna svojstva, omogućuje širu primjenu sustava na bazi CAC cementa.
Keywords
calcium aluminate cement
conversion process
slag
calcined clay
porosity
chloride diffusion
carbonation
sulphates
acids
Keywords (english)
kalcij aluminatni cement
proces konverzije
zgura
kalcinirana glina
poroznost
difuzija klorida
karbonatizacija
sulfati
kiseline
Language english URN:NBN urn:nbn:hr:237:302283 Promotion 2024 Study programme Title: Postgraduate doctoral study of the Faculty of Civil Engineering Type of resource Text File origin Born digital Access conditions Open access Terms of use Created on 2024-11-19 10:22:14
