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 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 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.

It is well known that glass fiber cement composites may suffer a loss of strength and toughness when exposed to natural environments. Even though buildings in Europe clad with GFRC panels have performed well for nearly 30 years now, this has restricted its use in certain circumstances because of a lack of confidence on behalf of the designer and specifiers. The loss of long term properties of GFRC is explained by two main phenomena: 0 The chemical attack of the glass fibers. 0 The morphological modification of the interfaces due to the growth of hydrates (Ca(OH)2 + CSH) which leads to em brittlement of the fibers in the matrix. The most widely used solution against the first type of attack is to use Alkali Resistance, AR, glass fibers with Cem-FIL being the original and Cem-FIL 2 giving the best long-term results. However, the way to obtain both constant flexural strength and ultimate strain (toughness) is to use both AR fibers and to modify the cementitious matrix in order to optimize the nature of the hydrate in the interface between the fiber and the matrix. Until recently, no totally satis-factory solution has been found even with the use of low alkali cements such as calcium sulpho-aluminate cement or portland cement with silica fume or flv ash. The CEM-FIL Star mix, developed by the Saint-Gobain group some 1 0 years ago, now has worldwide experience. It is based on using AR fiber with a specific type of the manmade, and therefore controllable, pozzolanic mate-rial, metakaolin, with a portland cement matrix. This reacts in a controllable way with the liberated lime, (calcium hydroxide), thus eliminating the main reason for the embrittlement of GFRC with time. By reacting with and re-moving this lime, long-term properties are improved.

The durability of two extruded thin sheet PVA fiber reinforced cement composites were investigated. The baseline composition contained silica fume and the other replaced the silica fume in the baseline composition with OPC. Compositions were subjected to aging in a 50% relative humidity room, immersion in a 50?C waterbath, and exposure to freeze/thaw cycling. Samples were tested primarily in the saturated condition and less frequently in the dry condition. Strength and toughness values were obtained from 3-point flexural and notched tensile tests. The effects of aging, silica fume content, and testing condition were considered. Each composition, tested in both the saturated and dry conditions and tested for all types of aging, experienced similar trends: a decrease in flexural strength and flexural first crack stress, an increase in tensile strength and tensile first crack stress, and a decrease in toughness values. Although both the non-aged and aged specimens experienced fiber pull-out, the mechanism of bond failure appears to be different. The contribution of silica fume was not significant as far as durability is concerned. Strength increased with drying, and toughness generally decreased.