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The structural use of steel fibers as the only principal reinforcing has been developed and refined for the last 15 years. Total replacement of traditional rebar is now common in applications like suspended slabs resting on a pile grid which spans from 3 m (10 ft) to 5 m (17 ft) each way. Generally, the span-depth ratio of the slabs in such applications ranges from 12 to 25. Although most of these slabs use the ground as a form only, some of them have been cast in elevated conditions without any contact with the ground to ensure total independence in the event expansive clay or gas hazards are present or could be present. More recently, steel fiber reinforced concrete has been used in suspended elevated slabs with a span-depth ratio equal to 30, and spans from 5 to 8 m (17 to 26 ft) length. The present article reviews the concrete mix design, the type of steel fiber, the dosage rate needed, the hardened concrete testing method based on current standard documents and round indeterminate panel slab tests. An example of steel fiber-reinforced concrete elevated slab is given and the design method is outlined in detail.

The case history presented in this paper describes a small sized project for design and construction of a macro synthetic fiber reinforced concrete (SnFRC) residential driveway with an average grade of 17%. The study highlights risks and benefits of choosing this material for this project. Five almost-equal lengths of SnFRC sections were placed in two groups 11 months apart. The delay between placements allowed for some experience to better analyze and determine if this was the best solution given the customer’s performance criteria and the difficult construction conditions. The design included a high cementitious content mixture with small aggregate, synthetic macro fibers, and air-entraining admixture. The resulting driveway was constructed down hill and has performed well in spite of minimal surface preparations and no jointing or saw cuts in the overlay. Some small cracking has occurred but has been of no consequence because the concrete has been held together by the synthetic fibers. For the construction of this residential driveway utilizing synthetic fiber reinforced concrete, the performance criteria was met, the construction schedule was on time, and the construction costs were significantly lower.

The effects of fresh state properties on the fiber dispersion characteristics of fiber-reinforced composites (FRCs) were studied by quantifying fiber segregation. Fresh state properties of concrete mixes were varied using different combinations of a plasticizing agent and viscosity modifier. A self-designed parallel-plate rheometer was used to obtain rheological parameters. Vibration was applied to the specimens and vibration times were varied to understand the effects of vibration on fiber segregation. An electrical characterization method, alternating current-impedance spectroscopy (AC-IS), was used to quantify fiber segregation in specimens. The relationship between fresh state properties and fiber segregation was evaluated.

Water loss from concrete results in volumetric shrinkage, which is significant at early ages. This shrinkage is particularly pronounced when the surface to volume ratio is large of the placements. Fibers, especially synthetic fibers are known to reduce cracking induced due to restrained plastic shrinkage. However, few studies have been conducted to monitor the early-age shrinkage of fiber reinforced concrete (FRC) using embedded sensors in the field. This study involved developing crack resistant FRC material in the laboratory using the bonded overlay technique developed at UBC and using it for a field project. Results from a plain concrete slab-on-grade section and a high volume fly-ash placement were used for comparison with fiber-reinforced concrete (FRC). Three sections were cast using synthetic fiber and their performance was monitored by reading strain signals from embedded sensors. Both traditional (electrical) and state of the art optical sensors were used. Optical sensors registered low strain values due to lack of bond with concrete. On the contrary, traditional electrical sensors clearly demonstrated the reduction in strain in FRC when compared to plain and fly-ash concrete. Specimens were cast on site for conducting tests in the laboratory. In addition, nondestructive tests were conducted on-site for monitoring performance of the slabs. These results are also presented in this paper.

The use of steel fiber-reinforced, silica-fume-modified concrete overlays and shotcrete for bridge repairs has long been the standard for Alberta Transportation (AT). Approximately 200 provincial bridges have been repaired with steel fiber reinforced, silica-fume-modified materials since 1984, mostly to decks, which had been exposed to aggressive conditions including freezing and thawing, de-icing salts, and moisture. The purpose of using steel fiber in bridge concrete repair materials was primarily to prevent or reduce repair cracks and to improve durability. Standard fiber lengths were 25 mm (1 in.) for shotcrete and 50 mm (2 in.) for overlays with standard fiber dosages of 60 km/m3 (100 pounds/yd3). Most of the repairs were done with superplasticized, silica-fume-modified, low water-cement ratio concrete mixes. This paper reports on the early historical development of the repair method basics and the lessons learned from monitoring bridge repairs. Conclusions are presented from AT’s Level 1 and Level 2 inspection data. Level 2 data quantifies several repair performance indicators, such as wide cracks, stains, delamination, spalls, patches, and debonds, as well as a breakdown of numerical condition ratings on important bridge elements. Crack data from Level 2 inspections was available from 154 silica fume modified bridge deck overlays, 124 of which contained steel fiber. The crack data was analyzed to assess the performance of fibers in reducing the amount of easily visible cracks: those wider than 0.3 mm (0.012 in.). The results showed that the steel fibers resulted in significant crack reduction and improved overlay durability and service life.