E. Badogiannis

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.

Effect of the Kaolin Particle Size on the Pozzolanic Behaviour of the Metakaolinite Produced

This paper reports an investigation of the effect of the particle size of kaolin on its transformation to metakaolinite. Kaolin from the island of Milos was either crushed or ground in order to produce four samples with different degrees of fineness (residue at 500 µm: 0–71.8%). The samples were treated thermally under different conditions in order to determine the optimum treatment conditions. The conversion of kaolinite to metakaolinite and the structural changes in the material during treatment were investigated by means of TG and XRD, respectively. Each sample was incorporated into a type I cement, at 20% by mass of cement, and the compressive strengths of the resulting blended cements were measured. It is concluded that the particle size of the raw kaolin does not affect the thermal conversion or the pozzolanic activity of the material. The use of crushed kaolin has many benefits since the furnace load can be increased, while the grinding process is needed only to reduce the size of the metakaolinite particles.

Chloride Penetration in Lightweight Aggregate Mortars Incorporating Supplementary Cementing Materials

The current research is aiming to investigate the chlorides’ penetration resistance of 9 different pumice lightweight aggregate mortars (LWAMs). The composition of the mixture is altered by the addition of metakaolin, fly ash, silica fume, and ground granulated blast furnace slag, substituting 10% and 20% of cement by mass. Workability and compressive strength of the mortars are studied together with durability parameters like water absorption due to capillary absorption and porosity. Moreover, the mortar resistance to chloride penetration is evaluated through non-steady-state chloride migration coefficient, complying to NT BUILD 492 standard. Summarizing all the laboratory test results, while the addition of metakaolin in the range of 20% led to better workability, higher compressive strength, lower sorptivity, and lower volume of open porosity, it did not improve the resistance against chlorides’ penetration.