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The use of fibers in a cement-based matrix can fundamentally improve its mechanical properties. Such improvement may lead to a new class of cement-based materials. Further developments depend o n an understanding of the interaction between different fibers and cement-based matrices. The current knowledge on the mechanical behavior of fiber-reinforced cement-based composites is sum mar ized . Toughening mec h anisms, interface properties, and tensile response of fiber-reinforced cementbased composites are presented. Various theoretical approaches used to describe the mechanical behavior of fiber-reinforced composites are reviewed. [

Recently acoustic emission (AE) techniques have been used to study crack propagation in materials. The application of these techniques to heterogeneous, quasi-brittle materials such as concrete requires a better understanding of how the signal generated from a microfracture is transformed due to wave propagation and due to the transducer response. In this study, piezoelectric transducers were calibrated using displacement transducers. The validity of an elastodynamic Green's function approach was examined for cement-based materials. The acoustic emission source was characterized using moment tensor analysis. Acoustic emission measurements were analyzed for center-cracked-plate specimens of mortar and concrete. It was observed that, as expected, the dominant mode of cracking was mode I (tensile). However, mode II (shear) and mixed mode cracks also occurred, perhaps due to grain boundary sliding and interface debonding. Microfractures appear to localize prior to critical crack propagation. Mode I cracks generally required more energy release than mode II and a smaller inclusion provided a stronger interface bond than the larger ones.

Fracture of quasi-brittle materials such as ceramics and cement-based materials can be described by an R-curve, defined as fracture resistance. The R-curve can be constructed as the envelope of the strain energy release rates (G). In this study, R-curve is defined as an envelope of G-curves obtained by varying the dimensions of identical specimens, while keeping the geometry and the initial flaw size constant. By approximating the G-curve with a second-order function of the crack length, a simple formulation of the R-curve is derived by solving a differential equation. Three parameters are needed for the proposed R-curve. These parameters can be obtained by testing a notched-beam specimen and using linear elastic fracture mechanics. The proposed R-curve simulates well the geometry dependency as well as other characteristics of the fracture response of quasi-brittle materials. [

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