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

To evaluate the influence of self-fibrillating macro-synthetic fiber reinforcement on the chloride penetration resistance of normal and self consolidating concrete mixtures, a total of 20 non-air entrained self consolidating concrete (SCC) mixtures with water to binder ratios between 0.4 and 0.45 (made using a ternary blend cement) and self-fibrillating macro-synthetic fiber dosages from 0.2 to 0.4% were evaluated. The chloride penetration resistance of all mixtures were evaluated using the Rapid Migration Test allowing the chloride diffusion coefficient to be calculated from the depth of chloride penetration which is determined visually. To evaluate the influence of cracking, which is typically more pronounced in SCC mixtures, shrinkage cracking resistance testing and chloride penetration testing on a cracked specimen were also conducted. At 28 days the chloride migration coefficient of all fiber reinforced self consolidating concrete (FRSCC) mixtures were slightly higher than the corresponding plain SCC mixtures; however at 120 days the FRSCC mixtures were slightly lower than the corresponding SCC mixtures. The superior performance of the FRSCC mixtures beyond 80-90 days is potentially due to reduced internal cracking due to the reinforcing effect of the fibers used in this study. The presence of plastic shrinkage cracking was shown to significantly influence the rate of chloride ingress locally around the crack. The influence of plastic shrinkage cracking was most appropriately modeled as an effective reduction in concrete cover equal to the crack depth. The influence of self-fibrillating macro-synthetic fiber addition on the service life of real structures was evaluated by incorporating the reduction in cover associated with plastic shrinkage cracks and chloride migration properties into corrosion modeling software (Life 365) to estimate the time to corrosion initiation in SCC with and without fibers with a reinforcement cover depth of 75mm which it typical for marine structures. The time to corrosion initiation for a non fiber reinforced mixture was calculated to be 18.6 years while the time to corrosion initiation for a mixture containing self-fibrillating macro-synthetic fiber at a modest dosage 3.7kg/m3(6.2lbs/yd3) was calculated to be 34.6 years, which represents a 85% improvement in service life.

Durability is nowadays a key-parameter in Reinforced Concrete (RC) structures. Several codes require that structures have a defined service life during which the structural performance must satisfy minimum requirements by scheduling only ordinary maintenance. Durability can be associated to permeability, defined as the movement of fluid through a porous medium under an applied pressure load, which is considered one of the most important property of concrete. Permeability of concrete is strictly related to the material porosity but also to cracking. The former is basically controlled by the water/cement (w/c) ratio while microcracks and cracks are related to internal and external strains or deformations experienced by the RC structures. Shrinkage, thermal gradients and any factor determining volumetric instability, as well as the loads acting on a structure, lead to both microcraking and visible cracking. It is well known that, after cracking, tensile stresses are induced in the concrete between cracks and, hence, stiffen the response of a Reinforced Concrete (RC) member under tension; this stiffening effect is usually referred to as “tension stiffening”. After the formation of the first crack, the average stress in the concrete diminishes and, as further cracks develop, the average stress will be further reduced. When considering Fiber Reinforced Concrete (FRC), an additional significant mechanism influences the transmission of tensile stresses across cracks, arising from the bridging effect provided by the fibers between the crack faces; this phenomenon is referred to as “tension softening”. Fibers also significantly improve bond between concrete and rebars and act to reduce crack widths. The combination of these two mechanisms results in a different crack pattern, concerning both the crack spacing and the crack width. The present paper describes results from a collaborative experimental program currently ongoing at the University of Brescia and at the University of Toronto, aimed at studying crack formation and development in FRC structures. A set of tensile tests (52 experiments) were carried out on tensile members by varying the concrete strength, the reinforcement ratio, the fiber volume fraction and the fiber geometry.

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.

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.