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Abstract
This study investigates the effects of fly ash and silica fume on the mechanical properties and microstructure characteristics of interfacial transition zone (ITZ) between macro-synthetic fiber and the bulk matrix of the fiber reinforced concrete. The experimental results show that the concrete is able to withstand significant post-cracking loads and undergo remarkable deflections under flexural loads due to the bridging effect of macro-synthetic fiber. The mechanical properties of concrete incorporating fly ash plus silica fume are much better than those prepared with no mineral admixtures or mono addition. The work of adhesion is an integrated index to evaluate the bonding behaviors between fiber and matrix, which exhibits a trend similar to that noted in the flexural toughness. The compound addition of fly ash and silica fume presents the most distinct improvement effects on microstructure of ITZ and the bonding behaviors between fiber and matrix. The amount of hydrated calcium silicate (C-S-H) gel and compaction of ITZ play key roles in the fiber - matrix interfacial bond and the mechanical properties of concrete.