International Concrete Abstracts Portal

Following a brief introduction on the definition of high-performance fiber reinforced cement composites (HPFRCCs), this paper suggests that HPFRCCs are very well suited for repair and rehabilitation applications. It describes the range of tensile properties currently achievable using HPFRCCs, focusing in particular on the trade-off between strength and strain capacity and the importance of large strains, as evidenced by quasi-strain hardening behavior and multiple cracking. Particular attention is given to describing the tensile stress-strain response of slurry infiltrated fiber concrete (SIFCON), and the parameters influencing that response such as type of fiber, type of matrix, fiber orientation, fiber length, and fiber bond. Also a brief summary of three representative applications involving the use of HPFRCCs in repair and rehabilitation is given, namely: the use of fibers in the tensile zone area of reinforced concrete beams to control cracking and improve durability; the use of SIMCON for repair and rehabilitation of reinforced concrete beams and columns to satisfy seismic requirements; and the use of SIMCON as a jacket in reinforced concrete columns, also to improve seismic resistance. It is concluded that exceptional structural performance such as strength and ductility, particularly in reinforced and prestressed concrete structures, can be achieved if the matrix material is an HPFRC composite.

High performance fiber reinforced cement composites (HPFRC) are defined as the materials which exhibit a postpeak strain hardening type of response with a multiple crack pattern. Such a ductile behavior makes the HPFRC an ideal material to be used in structural repair and retrofit for dimensional stability, tensile-load carrying capacity, impact resistance, flexibility and long term impermeability. The critical parameter for continuous fiber reinforced cementitious materials to obtain the high performance response is the minimum fiber volume ratio with well dispersed fibers. As long as continuous fiber composites have a sufficient number of fibers to bridge the cracks, strain hardening and multiple cracking can always happen. However, there is no single dominant parameter which can control the multiple cracking process in discontinuous fiber composites. Various parameters can affect the postpeak response of discontinuous fiber reinforced cementitious materials. They are related to fibers, matrix and the processing methods. Parameters relating to the reinforcement include the type of fiber, fiber length, fiber volume ratio, fiber orientation, state of fiber dispersion and the degree of adhesion to the matrix. These primary variables are in turn influenced by selection of the matrix type, presence of additives, and the processing conditions. The latter acts through controlling the state of dispersion, establishing a fiber design a high performance fiber reinforced cementitious repair material, the approach in which the repair will be carried out should be considered simultaneously.

This paper reports the results of an investigation on the performance of FRC-encased open web steel joists under cyclic loading. The system completely eliminates the need for any shear connectors between steel joists and surrounding FRC as well as that for conventional longitudinal and transverse reinforcing bars, all of which are quite labor intensive. Cyclic load test on some half-scale specimens consisting of composite beams with end connections were carried out. The parameters included the configuration of web steel elements, and the amount of steel in longitudinal and web elements of the joists. The results are most encouraging. interact in a y so as to provide stable hysteretic behavior with excellent energy dissipation and ductuility. The study indicates that shear strength of the composite beam can be remarkably enhanced by addition of structures. The flexural capacity is also considerably increased. It can be quite accurately calculated by analytical models based on full composite action.

Slurry infiltrated mat concrete (SIMCON) has recently emerged as a high performance steel fiber cementitious composite. Flexural strength, ductility and toughness of SIMCON were found to be superior to conventional steel fiber concrete. Being mechanically rolled at the plant, application of SIMCON in the field is facilitated. With high strength, ductility and ease of construction, SIMCON holds potential for application in repair of deteriorated highway bridge coupled with harsh weather conditions and presence of deicing chemicals result in continuous need for repair and rehabilitation. This paper discusses the potential advantages of SIMCON in repair applications. Mechanical properties of SIMCON including tensile stress-strain behavior and flexural load-deflection relation are reviewed. Investigation of the interfacial bond strength of SIMCON overlay and concrete substrate is focused in this project. To assess bond between plain concrete substrate and SIMCON, the effect of shear nails and latex was studied. Furthermore, air permeability of SIMCON via nondestructive testing was studied. Test results indicate the potential of SIMCON for use in repair and rehabilitation of pavements and bridges.

In most industrialized countries of the world, bulk of the future activity in the construction sector will be related to repair and rehabilitation of the existing structures. Given the general inadequacy of our present repair materials, much future research is needed towards developing high performance repair materials especially for executing durable thin repairs and patching. In this paper, polymer modified micro-fiber reinforced concrete composites are evaluated as repair materials by conducting CMOD controlled repair bond tests in uniaxial tension. A significant improvement in the bond strength and bond fracture energy due to both fiber reinforcement and polymer modification is noted. In addition, surface preparation emerges as one of the most important variables controlling the strength and fracture energy of the bond.