International Concrete Abstracts Portal

This CD-ROM contains six papers that were presented at sessions sponsored by ACI Committee 544 at the Spring 2008 ACI Convention in Los Angeles, CA, and the Spring 2009 ACI Convention in San Antonio, TX. The papers provide insight into the state of the art of the topic in academia, the industry, and real-life applications and cover some of the benefits of using fibers to enhance long-term performance of concrete with and without conventional reinforcement. 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-276

Self-consolidating concrete has become an important material in the concrete construction industry, however the modifications required to produce self-consolidating concrete (SCC) can significantly increase its susceptibility to cracking. This is an important durability issue when SCC is considered for use in reinforced concrete marine and highway structures. A common method of increasing the resistance of concrete to cracking is the addition of discrete monofilament macro-synthetic fiber reinforcement. However, the addition of fibers to SCC has the negative effect of reducing its self-consolidating characteristics. An experimental program was conducted to investigate the mixture modifications required to maintain the self-compactability of SCC with the addition of various rates between 0.2% and 0.4% by volume (1.8kg/m3 (3.0 lbs/yd3) - 3.6kg/m3 (6.0 lbs/yd3)) of a commercially available monofilament self-fibrillating macro-synthetic fiber. The effect of fiber addition rate on the plastic shrinkage resistance of SCC was also evaluated. The addition of fiber volume fractions ranging from 0.2% to 0.4% by volume were easily incorporated into several SCC mixtures (w/c =0.4, 0.42, 0.45) with adjustments made to the coarse/fine aggregate ratio and high range water reducer dosage rates. Interestingly, the addition of as little as 0.2% by volume of the monofilament self-fibrillating macro-synthetic fiber resulted in a 44.6% decrease in plastic shrinkage cracking area, when compared to its unreinforced counterpart, while also reducing the maximum observed crack widths by 43%. The addition of a higher fiber dosage (0.4% by volume) resulted in as much as a 70.4% reduction in cracking area and a 62% reduction in maximum crack widths for SCC mixtures with w/c ratios ranging from 0.4 to 0.45. From this study, it can be concluded that monofilament self-fibrillating macro-synthetic fiber reinforcement can be successfully incorporated into an SCC mixture to significantly increase its resistance to plastic shrinkage cracking while maintaining the workability expected from this type of concrete.

In the last decades, technical and scientific efforts have been done to increase the concrete strength, based on the assumption that more economic, lightweight, durable and good looking structures can be built. This strength enhancement, however, has been obtained by increasing the compactness of the concrete internal structure, resulting concretes with voids of smaller size, and lower connectivity than in concretes of current strength classes. Research and fire accidents have shown that the concrete failure of structures exposed to fire is as explosive as high is the concrete strength class, since the restrictions for the escape of water vapor from the interior of concrete increase with the concrete compressive strength. In the present work a fiber reinforced concrete of enhanced fire resistance is developed and its properties are characterized by experimental research. This concrete is intended to have enough strength for concrete precast tunnel segments, while the performance of the fibrous reinforcement system is evaluated in terms of verifying its possibilities for replacing, partially or totally, conventional reinforcement used in these structural elements.

Permeability and cracking affect the durability and integrity of a structure. The addition of reinforcing fibers changes the cracking process in cement based composites. The goal of this paper was to review the research work related to the effect of fiber reinforcement on tensile cracks and water permeability of cementitious composites. Factors affecting this relationship included matrix type, fiber type, geometry and volume fraction, and crack width. Water flow was studied through individual fiber and hybrid fiber reinforced composites. Widthcontrolled tensile cracks were induced for the polyvinyl alcohol (PVA) and steel fiber reinforced composite samples by feedback-controlled split tension or by feedback controlled wedge splitting. Then water flow was measured with a low pressure test set up. For the hybrid fiber reinforced composites containing blends of macro- steel and microsteel and PVA fibers tensile cracks were induced by uniaxial tension, while water was forced through the samples under a relatively low pressure. The addition of fibers had beneficial effects on water flow for cracks in the micron range. This was mainly due to changes in crack morphology compared to unreinforced composites and multiple crack development. Permeability thresholds were identified for the crack widths, which varied with the matrix type and the fiber type. Synergistic effects of micro- and macrofibers were obtained through engineered composites mix designs, and hybrid fiber reinforcement showed improved results in terms of mechanical performance and permeability of cracked cementitious composites compared to single fiber reinforcement.

The objective of this study was to investigate the possibility of using steel fiber reinforced concrete (SFRC) to enhance the performance of in the anchorage zone and to minimize the amount of mild steel reinforcement required by the code. For that purpose, different ratios per volume of different steel fibers were used in the study. The basic SFRC properties were obtained and then used in a thorough finite element analysis on 3D models of SFRC blocks representing the anchorage zone. The purpose of the numerical analysis was to define the proper dimensions of the need block specimens for laboratory testing, and to determine the locations of the internal and external strain gages in the block. Test results showed that the addition of steel fibers improved the loading capacity of the anchorage blocks. Further finite element analysis on 3D models proved that addition of 0.5 percent by volume of fiber was enough to reduce the mild steel reinforcement at the anchorage zone by about 40 percent. However, such an option needs to be dealt with caution. The addition of steel fiber to substitute mild steel could result in an abrupt failure in the anchorage zone.