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.

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.

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.

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.

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.