ABSTRACT
In this paper the R-CTOD curve behavior of a strain hardening cement composite (SHCC) is studied and compared to that observed in typical fiber reinforced cement composites (FRCCs). Whereas the latter is known to show a slow rising R-CTOD curve to a plateau value, SHCC is expected to show a rapid rise in the R-CTOD curve to even higher value. This contrast has practical implications. It relates to the fact that while good fracture toughness can be obtained in typical FRCC, access to this plateau value requires large development of its fracture process zone accompanied by wide crack opening. In SHCC, however, its high fracture toughness can be accessed with smaller crack extension and crack opening. The ductile fracture phenomenon observed in SHCC has an implication to the flexural strength of these materials. In an un-notched beam specimen, first cracking is accompanied by a strain concentration at the mouth of the crack. Because of the stress transfer capability of the reinforcing fibers in a
104 Li, Maalej and Lim
strain hardening material, stress redistribution will occur so that localized fracture will be delayed. Consequently, an expanded zone of matrix cracking (parallel to the first crack near the tensile face of the beam) must develop prior to localized fracture. Such an extensive volumetric cracking process must involve considerable energy absorption which must be related to the off-plane fracture energy recorded in a fracture specimen. This considerable energy absorption is expected to give rise to a high flexural (MOR) strength to tensile (first cracking) strength ratio. An experimental program consisting of third-point bending tests performed on a SHCC as well as typical FRCCs is designed to confirm this point. The results are also discussed in this paper.
