EFFECT OF FLY-ASH AND SILICA FUME ON COMPRESSIVE AND FRACTURE BEHAVIORS OF CONCRETE

The effects of replacing cement by fly ash and silica fume on strength , compressive stress-strain relationship, and fracture behavior of con crete were investigated. The investigation covered concrete mixes at d ifferent water-cementitious material ratios, which contained low and h igh volumes of fly ash, and with or without the addition of small amou nt of silica fume. It was found that fly ash substantially improved th e post-peak compressive behavior of concrete, with a relatively smalle r gradient in the descending part of the stress-strain curve. Low volu mes of fly ash improved the tensile strength of concrete. High volume fly ash concrete showed slightly lower tensile strength, but higher va lues of crack tip opening displacement and final mid-span deflection i n the fracture tests, with the corresponding K-IC and G(F) values simi lar to or higher than the plain cement concrete. A small amount of sil ica fume had a large positive effect on the cylinder compressive stren gth and tensile strength but less on the cube compressive strength, wh ile the fracture behavior of the resulting concrete was brittle. Impro ving interfacial bond between the paste and the aggregates in concrete had positive effects on K-IC, but did not necessarily produce higher G(F) values. (C) 1998 Elsevier Science Ltd.