International Concrete Abstracts Portal

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.

The performance of ultra-thin and thin concrete overlays on existing asphalt pavements, commonly referred to as whitetopping, requires the bond between the two layers to be maintained throughout the service life. Tensile stresses generated at the interface and adjacent to the joints due to slab curvature and the continuous nature of the underlying HMA contribute to the localized debonding of these two layers. A wedge splitting test was employed in this study to quantify the mode I loading induced fracture along the Portland cement concrete/hot mix asphalt interface of specimens designed specifically for this test. An analytical model is developed to characterize the response of the specimen under this loading condition. The model is used to assist in identifying the initiation as well as the growth of the interfacial crack, and for establishing the interfacial energy release rate. Using this model, the initiation as well as the growth of the interfacial crack is predicted for specimens with different surface textures at the interface.

The influence of fiber-reinforcement in concrete is most apparent after cracking has begun propagating through the fiber-reinforced concrete (FRC). The size-independent “initial” or specific fracture energy is defined as the energy per unit area to create a new crack surface; while the “total” fracture energy can be defined as the size- and geometry dependent amount of energy per unit area required for a specimen to exhibit complete separation failure at which negligible traction occurs across the new surface. While the initial fracture energy is used to define un-reinforced concrete, the total fracture energy parameter has been successfully utilized for characterizing the benefit of low-volume fractions of fiber-reinforcement for pavement and slab applications. This paper summarizes the main issues associated with using total fracture energy for FRC relate to the methodology for obtaining and interpreting the fiber component contribution as well as understanding the test methods and modeling options available.

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.

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.