International Concrete Abstracts Portal

This symposium CD-ROM contains eight papers that were presented at technical sessions sponsored by ACI Committees 544 and 237 at the 2009 ACI Fall Convention in New Orleans, LA. The topics of the papers cover aspects ranging from mixture composition and influence of fibers on the fresh state performance to the connection between fresh state behavior, fiber dispersion and orientation and mechanical properties of the fiber-reinforced composite to full-scale testing and development of prototype applications for structures and infrastructures. 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-274

Self-consolidating concrete (SCC) promises to shorten construction time while reducing the need for skilled labor. However, experience has shown that SCC may be prone to shrinkage cracking, which may compromise durability. In conventional concrete, fiber reinforcement has been used to control cracking and increase post-cracking tensile strength and flexural toughness. These benefits could be achieved in SCC without compromising the workability or stability, provided that the amount of fiber reinforcement is optimized. This project sought to evaluate the feasibility of fiber reinforced self-consolidating concrete (FR-SCC) for structural applications. Tests were conducted in the laboratory to assess the fresh and hardened properties of FR-SCC containing various types and concentrations of fiber. The results indicate that SCC with high flowability and some residual strength beneficial for crack control can be prepared for use in transportation facilities. The results of the experiments further show that, at optimal fiber additions, FR-SCC mixtures can have the same fresh concrete properties as traditional SCC mixtures. FR-SCC also demonstrates a considerable improvement in the residual strength and toughness of a cracked section. Though not specifically measured, increase in residual strength and toughness is expected to lead to control of crack width and length (ACI 544.1R, 1996). The increase in the FR-SCCs’ cracked section performance indicates that it can be expected to have better durability in service conditions than an identical SCC without fibers. In transportation structures FR-SCC can be used in link slabs, closure pours, formed concrete substructure repairs; or prestressed beams where end zone cracking has been an issue.

Applications of slabs supported on piles are quite common for areas where soil- structure interaction may create differential settlement or long term tolerance issues. An application for the use of steel fiber reinforced slabs that are continuous and supported on piles is discussed in this paper. The experience and design methodology for slabs on piles is further extended to floor slabs of multi-story buildings, where a high dosage of steel fibers (50-100 kg/m³, 84-168 lbs/ft3) is used as the sole method of reinforcement. Suspended ground slabs are generally subjected to high concentrated point loading (150 kN, or 33.7 kips) intensities as well as high uniformly distributed loadings (50 kN/m² or 1000 lb/ft2) and wheel loads. The span to depth ratios of the SFRSS is between 8 and 20 and depends on the loading intensity and the pile/column capacity. Standard procedures for obtaining material properties and finite element models for structural analysis of the slabs are discussed. Methods of construction, curing, and full scale testing of slabs are also presented.

Self-consolidating high performance fiber reinforced cementitious composites (SC-HPFRCC) combine the self-consolidating property of self-consolidating concrete (SCC) in their fresh state, with the strain-hardening and multiple cracking characteristics of high- performance fiber-reinforced cement composites (HPFRCC) in their hardened state. Two different classes of SC-HPFRCC are briefly introduced in this paper: concrete based and mortar based. They all contain 30 mm long steel fibers in volume fractions of 1.5% and 2%, and exhibit strain- hardening behavior in tension. These mixtures are highly flowable, non-segregating and can spread into place, fill the formwork, and encapsulate the reinforcing steel in typical concrete structures. Six concrete based SC-HPFRCC mixtures, with compressive strengths ranging from 35 to 66 MPa (5.1 to 9.6 ksi), were successfully developed by modifying SCC mixtures recommended in previous studies and using the available local materials. Spread diameter of the fresh concrete based SC-HPFRCC mixtures measured from the standard slump flow test was approximately 600 mm (23.6 in.). Strain-hardening characteristics of the hardened composites were ascertained from direct tensile tests. Three mortar based SC-HPFRCC mixtures with 1.5% steel fiber content were also developed and exhibited average compressive strengths of 38, 50 and 106 MPa (5.5, 7.2 and 15.3 ksi), respectively. Recent structural large scale laboratory applications (structural wall, coupling beams, panels etc.) made of SC-HFPRCC have demonstrated the applicability of these mixtures.

The addition of fibers into a self-consolidating concrete (SCC) matrix can take advantage of the superior fresh state performance to achieve homogeneous dispersion of the discontinuous wirelike reinforcement. Such a positive synergy between SCC and FRC technologies is of paramount importance to promote reliable structural applications. It has been furthermore shown that, through a well balanced set of fresh state properties of the mix, fibers can be effectively oriented along the direction of the fresh concrete flow. Superior mechanical performance of the material hence is obtained in the same direction. A “tailored” orientation of the fibers may be pursued to obtain a deflection-, or even a strain-hardening, behavior, which may be required by the specific application to be designed. With reference to a project on going in Italy, this paper details the steps of a “holistic” approach to the design of Self Consolidating High Performance Fiber Reinforced Concrete (SCHPFRC) elements. In this framework both the mix composition and the casting process are designed to the anticipated performance of the structural element, in the sight of an optimized material and structural efficiency. This would allow to pursue, in the design process, a desirable closer correspondence between the shape of an element and the function it performs in a structure assembly. A suitably balanced fresh-state performance of the fiber reinforced cementitious composite would allow to “mold” the shape of an element and, thanks to a tailored casting process, to orient the fibers along the direction of the principal tensile stresses resulting from its structural function.