An analysis of shear fracture toughness KIIc and microstructure in concretes containing fly-ash

The present study was focused on estimation of the fracture toughness in Mode II (shear) and internal microstructure of concretes containing 0%, 10%, 20% and 30% volume content additive of the Fly ash (FA). The addition of the FA changes the shear fracture toughness K-IIc. The regular value of the shear fracture toughness is included within the additive range from 0% to 23%. The volume content of the FA, corresponding to i.e. maximum increase of K-IIc is equal to 17%. If the FA content in higher than 23%, the composite becomes weaker as for response against to shear cracking. The most compact microstructure with well developed fibrous C-S-H phase were characterized by a concrete containing 20% FA additive. The biggest micro-cracks (from 2.5 to 3.0 mu m) in interfacial transition zone (ITZ) between paste and coarse aggregates were observed in concretes containing 30% FA, while the smallest one (to 700 nm) in concretes with 20% FA additive. Crown Copyright (C) 2013 Published by Elsevier Ltd. All rights reserved.