International Concrete Abstracts Portal

SP190 The 11 papers in this Special Publication were presented at the ACI Spring Convention in Chicago, Illinois in March 1999, and represent worldwide advances in the development of high-performance fiber reinforced thin sheet products. The applications addressed include curtain walls, pipes, roof tiles, and repair/retrofit of existing structures. The manufacturing processes are discussed as well as the variety of natural and manufactured materials used.

The influence of fiber length on tension and flexural behavior of extruded and cast cement composites was examined for PVA (hydrophilic) fibers and polypropylene (hydrophobic) fibers. The fiber-matrix interface, fiber surface, and microstructure of the composite cross-section were characterized by SEM. Opposite trends were obtained for the cast and extruded composites with increasing fiber length. For the extruded composites, decreasing fiber length increased flexural and tensile response, whereas for the cast composites increasing the fiber length increased the flexural and tensile response. These differences were found to be a result of differences in fiber-matrix bond properties and fiber distribution. The extruded composites showed a stronger fiber-matrix bond compared to the cast composites. This led to differences in the fiber failure mechanism: fiber rupture of the 6mm fibers in the extruded composite, and fiber pullout of both fiber lengths in the cast composites and for the 2mm fibers in the extruded composites.

The steel free bridge deck slab technology has seen its real-life applications in a span of less than ten years from its initial conception. Indications are that more and more bridges will be built using this concept around the world, especially in places where corrosion of reinforcement is a serious concern. In this paper, results of an experimental project carried out at the University of British Columbia, where a full scale bridge deck was tested with carbon fiber reinforced cement (CFRC) permanent formwork, are described. The bridge deck had 0.4% of fibrillated polypropylene fiber reinforcement but no traditional steel reinforcement. The carbon fiber used in the formwork was a pitch-based fiber with a moderately high modulus of elasticity and tensile strength. The deck slab was tested at various locations under a simulated concentrated wheel load and the load vs. deflection characteristics were recorded. While the bridge deck failed, as expected, in a punching shear mode at a load several times higher than the design load, the bond between the CFRC formwork and the concrete deck was identified as a weak link in the system

The effect of material constituents on the performance of fiber reinforced cementitious thin sheets was studied in order to examine the possible trade-off between cost and performance in cement-based building product development. A variety of materials were incorporated into fabricating cementitious thin sheets. The variables included types of fibers (glass, polyethylene terephthalate, polyolefin, or polyvinyl alcohol), types of sand (marble, silica or fly ash) and percent content, mixing method (dispersive or non-dispersive), latex types (MMA or SB), cement types (Type I or Type III), mineral additives (metakaolin or silica fume) and curing conditions (moisture or steam). Twelve batches of thin sheets with 3% fibers by volume for each were prepared by extrusion processing and three-point bending tests were conducted to evaluate the strength and toughness. The purpose of the study was to establish several mix designs for extrusion production of high performance fiber reinforced cementitious thin sheets at compatible cost.

A class of new structural materials with a significant degree of ductility and strength are introduced that are durable, strong, and cost effective. High fiber content cementitious materials (FRC materials) are manufactured using a computer controlled closed loop system for pultrusion and filament winding. Composites consisting of unidirectional lamina, and [0/90/0] are manufactured. In addition, sandwich composites with a lightweight aggregate core and 0/90 lamina as the skin elements are studied. Mechanical response of laminates is measured using closed loop uniaxial tensile and flexural tests. Results indicate that tensile strength of composites containing 5% alkali-resistant (AR) glass fibers can exceed 40 MPa. The ultimate strain capacity can also be increased to more than 2% using cross plies at various orientations. Significant cost savings and weight reduction may be achieved by replacing the inner layers of the boards with a lightweight aggregate mixture at a marginal loss of strength. The ultimate strain capacity of the composites is a function of ply orientation, thickness, and stacking sequence. Various mechanisms of delamination, debonding, and crack deflection are identified, resulting in an ultimate strain capacity of 2%, and a fracture toughness as much as two orders of magnitude higher than the conventional FRC materials. The extent of matrix cracking, ply delamination, and crack deflection mechanisms are studied by means of fluorescent microscopy.