Alternative binders have economic and ecological advantages as well as a variety of positive properties (high resistance to aggressive media, high compressive strength, high frost resistance, low or fast release of heat of reaction, low porosity or high temperature resistance). However, the properties are decisively depending on the nature of the binder type. For alkali activated ground granulated blast furnace slags (GGBFS), the chemical-mineralogical composition of the slags as well as the type and dosage of the activator are of vital importance here.
First target of this thesis was therefore the investigation of the influence of different GGBFS parameters, in particular the chemical composition (CaO/SiO2 ratio, TiO2 content, Al2O3 content, MgO content), the melting temperature as well as the mineralogical composition (glass content) on the development of reaction heat, compressive strength and reaction products with selected alkaline activators. As a result, the individual GGBFS characteristics could be divided into 4 categories. The melting temperature and the TiO2 content have no influence on the setting behavior and the reaction products, while that of the glass content and the MgO content is low. An increased Al2O3 content has a stronger effect and shows a dependence on the selected activator. However, the CaO/SiO2 ratio of the GGBFS has the greatest influence, independent of the activator.
For an economical use of alkali activated slags (AAS), for example for concrete applications, their durability properties are important, too. Since mortars and concretes with AAS as binders have a 10-fold increase in alkalis compared to systems with Portland cement, the question arises whether there exists an increased risk of an alkali silica reaction (ASR) in these systems.
The second target of this work was to investigate the influence of the alkaline activator, mainly alkali silicate, with respect to the water glass module (molar ratio SiO2/M2O, M = Li, Na, K), alkali concentration and alkali ion (Li, Na, K) on an ASR. For this purpose, mortars from an industrial GGBFS, various activators, as well as borosilicate glass beads with defined alkali sensitivity were stored and observed in a cloud chamber for several months at 40 °C. The conclusion is that the water glass module has a considerable influence on the initial shrinkage and later expansion and influences the effect of the alkali ion (sodium and potassium) as well as the alkali concentration.
|School:||Technische Universitaet Berlin (Germany)|
|Source:||DAI-C 81/4(E), Dissertation Abstracts International|
|Keywords:||GGBFS, CaO, TiO2, SiO2|
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