Th. Perraki

Thermal treatment of kaolin: the effect of mineralogy on the pozzolanic activity

This paper reports an investigation on the effect of mineralogy on the pozzolanic activity of fired kaolin. Representative samples of Greek kaolin (Milos Island) and a commercial kaolin of high purity are studied. The samples are tested by X-ray diffraction (XRD), Differential Thermal Analysis (DTA) and Infrared (IR) Spectroscopy in order to determine their mineralogical composition and structural differences. Calcination of samples is carried out at 650°C for 3 h. The decomposition of kaolinite and alunite is recorded using methods of thermal analysis. The resultant products are identified by XRD. The reactivity of the thermally treated samples is evaluated based on Chapelle test. It is concluded that the pozzolanic activity of metakaolinite is strongly related to the crystallinity of the original kaolinite. Well-ordered kaolinite is transformed into less reactive metakaolinite.

The effect of natural zeolites on the early hydration of Portland cement

Abstract In this work, the effect of zeolite, coming from Pentalofos area, Thrace, Greece, on the hydration of cement is examined. The experimental part comprises three stages: In the first stage a complete mineralogical characterization of the zeolite was performed. In addition, the pozzolanic reactivity of the zeolite was evaluated on the basis of Chapelle test. In the second stage, pastes of Portland cement, incorporating 0%, 10%, 20% and 30% per weight of fine zeolite were prepared. The pastes were water-cured at 20 °C, for 1, 2, 7 and 28 days. Finally, the hydration rate and products were studied by means of X-ray diffraction and Fourier transform infrared spectroscopy, in combination with thermoanalytical methods (TG/DTG and differential thermal analysis). As it is concluded, the examined zeolite consists mainly of “heulandite type II” and shows a good pozzolanic reactivity (0.555 g of Ca(OH) 2 per gram of zeolite, according to the Chapelle test). The incorporation of zeolite in cement contributes to the consumption of Ca(OH) 2 formed during the cement hydration and the formation of cement-like hydrated products.

Mineralogical study of zeolites from Pentalofos area, Thrace, Greece

Abstract The zeolites of the Pentalofos area, Thrace, Greece, were studied by optical microscopy, X-ray diffraction (XRD) and Fourier Transform IR (FTIR) spectroscopy, in combination with thermoanalytical methods (thermogravimetric analysis (TG/DTG) and differential thermal analysis (DTA)). Their main mineral constituent (>90%) is “heulandite type-II”, an intermediate type of the isomorphous series heulandite–clinoptilolite end members. Feldspars, muscovite, biotite, quartz, and cristobalite were also detected. Traces of smectite were found in only few samples. The cation exchange capacity (CEC) of the Pentalofos zeolites (119 to 152 meq/100 g), as well as their low temperature dehydration behavior (during heating up to 350 °C, 15 of ∼22 molecules H2O are removed) are also characteristic for an intermediate member of the heulandite–clinoptilolite zeolite (“heulandite type-II”). These properties make them a powerful tool in the decontamination of waters and soils, in agriculture, in cement industry, etc. Moreover, this zeolite deposit is of a great economic interest, considering that it is the richest among the zeolite formations in Northeastern Greece (4.7×106 tons, with a zeolite content higher than 90%).

Secondary raw materials in cement industry

The sintering and hydration processes of a modified cement raw mix were examined using thermal analysis techniques. One reference and four modified mixtures, prepared by mixing the reference sample with 0.5, 1.0, 1.5 and 2.0 % w/w of a wolframite-stibnite mineral were studied. The clinkering reactions were recorded and the total enthalpy change during the sintering was determined by means of a differential scanning calorimetry. The combined water and the Ca(OH)2 content in samples hydrated for 1 to 28 days were determined, using thermogravimetry. As it is concluded, the effect of the added mineral on the sintering and hydration reactions can be fully recorded and evaluated using thermal analysis.

Synthesis of calcium aluminates through the polymeric precursor route

The Pechini method is a polymeric precursor route for the synthesis of polycrystalline ceramics of high purity. The conventional solid state synthesis of calcium aluminate compounds requires long-term lasting sintering at high temperatures. In this study, the Pechini method was applied for the preparation of pure CaO.Al2O3 and 3CaO.Al2O3. Solid state synthesis was also used in order to compare the final products obtained by the two methods. The intermediate and final products obtained were characterized by XRD and FTIR spectroscopy. It was concluded that the Pechini method can be successfully applied for the preparation of high purity CaO.Al2O3 and 3CaO.Al2O3. The formation of 3CaO.Al2O3 and CaO.Al2O3 requires three-hour sintering at 1000°C and 900°C, respectively. The main intermediate product was 5CaO.3Al2O3 in the case of 3CaO.Al2O3, while in the case of CaO.Al2O3 there were no other crystalline intermediate products. The samples prepared through solid state synthesis, contain a considerable amount of secondary phases, even after sintering at 1350-1400°C for more than 15 hours.

The Effect of Synthesis Parameters on the Structure and Properties of Metakaolin Based Geopolymers

In the present work the geopolymerisation of metakaolin under varying conditions is investigated.The experimental part comprises the following parts: i) the synthesis of metakaolin based geopolymers and the investigation of the effect of the Si/Al ratio and the kind of alkali ion on the development of the compressive strength and ii) the characterization of the geopolymers by means of XRD, FTIR and SEM. As it is found the development of the compressive strength is strongly affected by the Si/Al ratio in the starting material and the kind of alkali metal, with the maximum being 70.1 MPa for a Si/Al ratio equal to 2.00. The Na- geopolymers show higher compressive strength compared to the NaK-geopolymers. Finally, low Si/Al ratios favour the formation of crystalline compounds (mainly zeolites), while Si/Al ratios higher than 1.5 lead to the formation of amorphous materials.

Synthesis and Characterisation of Slag Based Geopolymers

In the present work the geopolymerisation of blast furnace slag (GGBS) under varying conditions is being investigated. The experimental comprises the following parts: i) dissolution of slag in alkaline media and the investigation of the effect of the alkali ion (K or Na) on the dissolution of Al+3 and Si4+, ii) synthesis of slag based geopolymers and the investigation of the effect of the Si/Al ratio and the kind of alkaline ion on the development of the compressive strength and iii) characterization of geopolymers by means of XRD, FTIR and SEM/EDS measurements. As it is concluded, blast furnace slag geopolymers exhibit high compressive strength, with the maximum being 112.7±2 MPa. The Si/Al ratio of the starting material is found to affect strongly the development of the geopolymer compressive strength. The microstructure of slag–based geopolymers and the incorporation of Ca in the geopolymer matrix are also discussed.