International Concrete Abstracts Portal

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.

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 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.

Shrinkage cracking of self-compacting concrete (SCC) overlays with and without steel fibres has been assessed through laboratory testing and theoretical analysis. Test results verified that steel fibre reinforcement has a crack width limiting effect. However, the contribution in case of fibre contents up to 0.75 vol% was not found to be sufficient to distribute cracks in situations where bond to the substrate was nonexistent. Thus, even higher steel fibre contents (or other types of fibres) are required in order to control cracks. A distributed pattern of fine cracks was however obtained even for unreinforced SCC within bonded areas of the overlays. This implies that steel fibres, or other crack reinforcement, are not required if high bond strength is obtained. An analytical model, proposed to assess the risk of cracking and to predict crack widths in overlays, was found to give reasonable correlation with experimental results.

In the present work the tensile behavior of a self-compacting concrete reinforced with two hooked ends steel fiber contents was assessed performing stable displacement control tension tests. Based on the stress-displacement curves obtained, the stress-crack width relationships were derived, as well as the energy dissipated up to distinct crack width limits and residual strengths. The number of effective fibers bridging the fracture surface was determined and was compared with the theoretical number of fibers, as well as with the stress at crack initiation, residual stresses and energy dissipation parameters. In general, a linear trend between the number of effective fibers and both the stress and energy dissipation parameters was obtained. A numerical model supported on the finite element method was developed. In this model, the fiber reinforced concrete is assumed as a two phase material: plain concrete and fibers randomly distributed. The plain concrete phase was modeled with D solid finite elements, while the fiber phase was modeled with discrete embedded elements. The adopted interface behavior for the discrete elements was obtained from single fiber pullout tests. The numerical simulation of the uniaxial tension tests showed a good agreement with the experimental results. Thus, this approach is able of capturing the essential aspects of the fiber reinforced composite’s complex behavior.