Improvement of the durability of glass fiber reinforced cement using blended cement matrix

Blended cements prepared with two fly ashes were used as matrices in glass fiber reinforced cement (GRC) composites in an attempt to improve their durability. The hydrated matrices from the two blended cements investigated here had similar strength and composition. Both fly ashes reduced the Ca(OH)₂ content to the same extent but in both cases the pH level was only slightly reduced compared to the portland cement matrix. In spite of these similarities, the GRC prepared with one fly ash showed considerable improvement in durability while the other one had only a small positive effect. SEM observations indicated that the improved durability in one case was associated with modification in the microstructure of the hydration products deposited in between the glass filaments, resulting in a much more open structure compared to that of portland cement matrix or the other blended cement. It is therefore suggested that the potential of the blended cement matrix to improve the durability of GRC is associated with its ability to modify the microstructure of the paste at the glass interface. This characteristic is not necessarily related to the overall composition of the blended cement matrix and to the reactivity of fly ash with Ca(OH)₂.