International Concrete Abstracts Portal

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.

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.

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.

Editor: Christian Gaedicke

This CD contains 10 papers that were presented during a session sponsored by ACI technical committee 446 at the Spring Convention in 2012 in Phoenix, AZ. The papers focus on the implementation of fracture mechanics techniques in fiber-reinforced concrete, fiber-reinforced polymers, bonding, large structures, beam shear, pavements, and concrete deterioration. Where applicable, the papers compare modeling results with experimental tests.

Note: The individual papers are also available. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP-300

Behavior of RC deep beams is very complex, and several factors influence its shear strength. This paper discusses on analytical investigations on the shear strength of reinforced concrete (RC) deep beams. An expression for estimating the ultimate shear strength of RC deep beams provided with shear reinforcement, considering the beam depth including all other influencing parameters has been developed. The proposed ultimate shear strength estimation also considers the shear transfer mechanism of RC deep beams through a refined strut-and-tie model retaining the generic form of the modified Bazant’s size effect law, using a large selected experimental data base. The shear strength of RC deep beams has been predicted accurately using the square root of beam depth. The proposed size dependent equation is simple and accurate for RC deep beams with a/d ratio less than 2.0. Various parameters such as strut angle, flexural reinforcement ratio, shear reinforcement, both vertical and horizontal and beam depth have been accurately accommodated in the present size dependent shear strength expression using refined strut-andtie model. The prediction of the shear strength of RC deep beams has been observed to be reasonably agreeable with the experimental observations.