Capillary rise properties of porous geopolymers prepared by an extrusion method using polylactic acid (PLA) fibers as the pore formers

The geopolymers were prepared from sodium silicate, metakaolinite, NaOH and H(2)O at SiO(2):Al(2)O(3):Na(2)O:H(2)O of 3.66:1:1:x, where x=8-17, and curing temperatures of 70-110 degrees C. Since the bending strength of the geopolymers was highest (36 MPa) where H(2)O/Al(2)O(3) = 9 and the curing temperature=90 degrees C, these conditions were adopted. The porous geopolymers were prepared by kneading PLA fibers of 12, 20 and 29 mu m diameter into the geopolymer paste, at fiber volumes of 13-28 vol%. The resulting paste was extruded using a domestic extruder, cured at 90 degrees C for 2 days then dried at the same temperature. The PLA fibers in the composites were removed by alkali treatment and/or heating. The highest capillary rise was achieved in the porous geopolymers containing 28 vol% of 29 mu m fibers. The capillary rise of this sample, estimated by the equation of Fries and Dryer(1) was 1125 mm. (C) 2010 Elsevier Ltd. All rights reserved.