Pozzolanic reactivity of pure calcined clays: Fid-Bau Portal

Pozzolanic reactivity of pure calcined clays

Hollanders, Sofie / Adriaens, Rieko / Skibsted, Jørgen / Cizer, Özlem / Elsen, Jan

AbstractEight reference clay samples, 4 kaolinitic, 3 smectitic and 1 illitic clay, were purified and thermally treated in order to determine their pozzolanic reactivity in cementitious materials. The clays were calcined in a fixed-bed electrical furnace at temperatures ranging between 500°C and 900°C. Both raw and calcined clays were characterized by ICP-OES, XRD and BET techniques. Their pozzolanic reactivity was evaluated with clay-lime pastes after 3, 7, 14, 28, 56 and 90days using thermogravimetry (TGA). The results indicate that all kaolinitic clays are highly reactive at a broad range of firing temperatures (500–900°C). The degree of ordering of the raw kaolinite influences the optimal activation temperature and the rate of the calcined clay-lime reaction. The smectitic clays possess a clear optimal calcination temperature of 800°C. Ca-rich smectites are proven to be somewhat more reactive than Na-rich smectites. However, even at 800°C, its reactivity is significantly smaller compared to kaolinite. Hectorite and illite calcined at an optimal temperature of 800 and 900°C, respectively, exhibit poor pozzolanic reactivity.

Highlights•Degree of ordering controls the reaction rate and optimal activation temperature.•Interlayer cation of montmorillonite influences the pozzolanic reaction.•Chapelle test overestimates pozzolanic reactivity of smectitic and illitic clays.