Crack resistance of cement-based materials under flexural stresses was studied experimentally in order to back-calculate the tensile properties. Monotonic and cyclic tests were performed on plain and fiber-reinforced concrete materials. A methodology based on the R-Curve approach is proposed that implements the measurement of an effective crack length by the correlation of apparent compliance of specimens through loading and unloading cycles. Closed-loop three-point bending tests were conducted on notched beam specimens with crack mouth opening displacement (CMOD) as the controlling signal. The tests and the associated analyses were applied to several cases to evaluate the effects of curing time (strength development) as well as fiber-reinforcement (using AR-glass fibers) on the fracture behavior of concrete. The results showed that the fracture-based back-calculation method is relatively similar and comparable to predicted tensile stress-strain responses of other well-known methods.

This article presents a computational fracture mechanics analysis of reinforced concrete deep beams using nonlinear fracture mechanics to study load deflections, cracking patterns and size effects observed in experiments of normal and high-strength concrete deep beams with and without stirrup reinforcement. The article describes the development of a numerical model that includes the nonlinear processes that contributes to the strength of any concrete beam such as compression and tension softening of concrete, bond slip between concrete and reinforcement, and the yielding of the longitudinal steel reinforcement. Because the complexities that are present during the meshing when multiple cracks are in the system, the development also incorporates the Delaunay refinement algorithm to create a triangular topology that is then transformed into a quadrilateral mesh by the quad-morphing algorithm. These two techniques allow automatic remeshing using the discrete crack approach. Nonlinear fracture mechanics is incorporated using the fictitious crack model and the principal tensile strength for crack initiation and propagation. The model has been successful in reproducing the load deflections, cracking patterns and size effects observed in experiments of normal and high-strength concrete deep beams with and without stirrup reinforcement.

This paper reviews a recently developed finite weakest link model of strength of concrete structures, which fail under controlled load at macro-crack initiation from one representative volume element (RVE). The probability distribution of RVE strength is derived from the well-established transition rate theory and a hierarchical multi-scale transition model. The model predicts that the strength distribution of concrete structures depends on the structure size and geometry, transiting from a predominantly Gaussian distribution to a Weibull distribution as the structure size increases. It is shown that the present model agrees well with the strength histograms of Portland cement mortar measured by Weibull, which consistently deviate from the classical Weibull distribution. The importance of size effect for the reliability analysis of large concrete structures is then demonstrated through the analysis of the failure of the Malpsset Dam. Both the present model and the available experimental data invalidate the three-parameter Weibull distribution for concrete structures.

It has been well over thirty years since Hillerborg and Bazant presented their landmark papers (cohesive crack and size effect models respectively), and thirty years since the author submitted his Ph.D. dissertation on the application of fracture mechanics to concrete, (Saouma, 1980). Yet, since then, the practical applications of fracture mechanics to concrete structures have been few and far in between. In this paper, the author shares his experience in trying to apply fracture mechanics not only to concrete structures, but also to other \neighboring" materials such as polymers and ceramics, and he argues for improved collaboration with adjacent disciplines. The underpinnings (experimental, computational) of reported applications will be briefly highlighted. Finally, the paper concludes with a personal assessment of the current of state in the application of fracture mechanics to concrete structures and venture in some recommendations.

This research describes a computational model developed to investigate failure at the interface of two layers of a newly- constructed concrete composite pavement under wheel and thermal loads. This failure is often referred to as "debonding." The likelihood of debonding is considered in light of construction practices and heterogeneity in the concrete layers. Simulations determined that for debonding to occur, significant degradation of interfacial properties in combination with extreme, unrealistic thermal strains would be required. These simulations support observations of composite concrete pavements in Europe, where no debonding has been noted in over fifty years of application.