International Concrete Abstracts Portal

This CD-ROM contains 10 papers that were presented at sessions sponsored by ACI Committee 544 at the Spring 2011 ACI Convention in Tampa, FL. The topics of the papers cover durability aspects of fiber-reinforced concrete, ranging from permeability, shrinkage cracking, long-term behavior in chloride environment and resistance to chloride penetration, as well as applications of fiber-reinforced concrete for coupling beams for highrise core-wall structures, beams for bridges, panels and suspended foundation slabs. Note: The individual papers are also available. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP-280

During its service life, a reinforced concrete structure seldom sees the maximum loads it is designed to withstand. Nonetheless, failure of reinforced concrete does occur, and it is mainly due to deterioration in the quality of concrete with time. Of particular concern is the transport of deleterious fluids, which is an immediate cause of corrosion of the embedded steel and resultant loss in performance. While cement-based composites are inherently porous, the permeability of concrete is further aggravated by progressive cracking under service loads. Thus, in this study, water permeability and ultrasonic wave velocity measurements were carried out on hollow cylinders made of cement-based concrete and mortars simultaneously subjected to compressive stress. The level of stress was varied from 0–90% of the compressive strength. The role of fibre reinforcement was investigated through polypropylene microfibres incorporated at 0.25% volume fraction. It was found that the coefficient of permeability and the wave velocity are sensitive to a threshold stress value. Fibres delayed the onset of this threshold for both these parameters. Based on the experimental results, an empirical correlation is made between the water permeability and ultrasonic wave velocity.

Reinforced concrete structures exhibit frequent deterioration problems that are related to the penetration of water, air and deleterious agents into the concrete. Cracking initiated by internal and external loads applied to the structures favors a deepen penetration of gaz and fluids and accelerates deterioration processes. The impact of cracking and load application on concrete durability can be evaluated with water permeability measurement. In this project, a novel device was used to evaluate water permeability of reinforced concrete specimens made in normal strength concrete (NSC) and fiber reinforced concrete (FRC). The permeability was measured during the application of a tensile load on the specimens. Complementary tensile tests permitted to characterize the crack pattern and the crack openings in the specimens under loads. Experimental results were combined to collectively analyze measurements of permeability, crack opening and stress in reinforcement were combined to establish correlations. The permeability of the FRC was approximately 3 times smaller than the one of the NSC at an equivalent loading level in the reinforcement of the specimens. Moreover, for the same permeability, admissible stresses in the reinforcement can be at least 75 MPa higher when it is embedded in FRC rather than in NSC. It means that for an equivalent durability, an engineer can design structural members with the studied FRC with less reinforcement or to withstand higher loads at serviceability.

Steel fiber-only structural reinforcement at a rate of 40-50kg/m³(66-82lb/cu yd) has been used as the sole method of reinforcement of suspended structural slabs which are slabs cast on the ground and supported by a grid of piles. Typical applications include warehouses, factories, office and condominium buildings, towers and, as shown in this paper, sport arenas. The span to depth ratio is between 8 to 22. The 60,000 seating capacity Swedbank Arena in Solna (Stockholm, Sweden) is a project located on a site which does not show any available ground bearing capacity so that the site has been piled completely prior to installing the foundation slab. The pile grid lies between 3m (20ft) and 7m (25ft) distance and the slab’s thicknesses equal 300mm(12in) and 350mm(14in). The suspended foundation slab consists of 16,000cu.m(20,700cu yd). worth of steel fiber reinforced concrete, the total area being 50,000m²(550,000sq.ft): the grass area for the soccer game or as exhibition and concert hall, the technical rooms, and the external parking area, respectively highlighted in green, pink and orange in Fig.3.

Experimental and analytical studies that led to the incorporation of strain-hardening, high-performance fiber reinforced concrete (HPFRC) coupling beams in the design of a high-rise core-wall structure in Seattle, WA, are described. A total of eight HPFRC coupling beams with span-to-depth ratios ranging between 1.75 and 3.3 were tested under large displacement reversals. The tension and compression ductility of HPFRC materials allowed an approximately 70% reduction in diagonal reinforcement, relative to an ACI Building Code (318-08) compliant coupling beam design, in beams with a 1.75 span-to-depth aspect ratio and a total elimination of diagonal bars in beams with a 2.75 and 3.3 aspect ratio. Further, special column-type confinement reinforcement was not required except at the ends of the beams. When subjected to shear stress demands close to the upper limit in the 2008 ACI Building Code (0.83 f’c [MPa] (10 f’c [psi])), the coupling beams with aspect ratios of 1.75, 2.75 and 3.3 exhibited drift capacities of approximately 5%, 6% and 7%, respectively. The large drift and shear capacity exhibited by the HPFRC coupling beams, combined with the substantial reductions in reinforcement and associated improved constructability, led Cary Kopczynski & Co. to consider their use in a 134 m (440 ft) tall reinforced concrete tower. Results from inelastic dynamic analyses indicated adequate structural response with coupling beam drift demands below the observed drift capacities. Also, cost analyses indicated 20-30% savings in material costs, in addition to much easier constructability and reduced construction time.