Batches containing 5 kg of Serbian medium-quality kaolin clay were mechanically treated in a conventional ball mill for 10, 30, 60, 120, 600 and 1200 min of milling time. High reactive pozzolanic addition was obtained as a result of a number of physicochemical changes induced by milling, namely particle size reduction, specific surface area increase, amorphization/dehydroxylation of kaolinite phase and homogenization of clay constituents. The main characteristics of the pozzolanic material obtained after 1200 min of milling were: median particle size of 635 mu m, specific surface area of 21.75 m(2) g(-1), total pore volume of 0.0580 cm(3) g(-1), pozzolanic activity (compressive strength) of 14 MPa, and reactive silica content of 33.3 wt.%. Continuous increase of pozzolanic activity, despite the agglomeration of particles that was accompanied with specific surface area decrease when milling time was prolonged, could be explained by kaolinite amorphization as well as the mechanical activation of quartz. (C) 2014 Elsevier B.V. All rights reserved.