REACTION OF ALKALI-RESISTANT GLASS-FIBERS WITH CEMENT .2. DURABILITY IN CEMENT MATRICES CONDITIONED WITH SILICA FUME

In Part 1 of this paper four fibre failure modes were distinguished: mass dissolution, hydroxylation, crystallisation of the passivating layer, and notching by Ca(OH)2 crystals. Hydroxylation is associated with the high pH of the pore fluid of Portland cement, and one way of reducing the alkalinity, as well as of sharply reducing the Ca(OH)2 content of the cement, is to add silica fume, which is commercially available as micrometre or submicrometre sized glassy particles. In the present study, composites containing 15% silica fume were prepared and cured at 20-degrees or 55-degrees-C for up to 180 d, but the overall beneficial effect was found to be slight. Although it greatly inhibits or eliminates notching damage, silica fume does not reduce the internal pH sufficiently to inhibit other attack mechanisms. Elastic modulii are correlated with electron optical studies, showing specific damage mechanisms.