International Concrete Abstracts Portal

To evaluate the flow characteristics of macro-synthetic fiber-reinforced self consolidating concrete (MSFRSCC), a total of 20 non-air entrainment self-consolidating concrete (SCC) mixtures with varying w/c ratios, macro-synthetic fiber lengths, and fiber dosages rates were evaluated. The flow characteristics of each mixture were evaluated using our typical SCC workability test methods: slump flow, filling capacity, L-box, and V-funnel tests. The plastic shrinkage cracking resistance, compressive strength and flexural strength of each mixture were also evaluated. The objective was to develop an understanding of the factors that influence the flow characteristics of MSFRSCC and determine if criteria set for conventional SCC can be applied to MSFRSCC. The testing results demonstrated that fiber lengths of 50 mm cause significant internal friction leading to mixture stability issues when attempting to increase the volume of high range water reducer to produce acceptable slump flow values without viscosity modifying admixtures. Reducing fiber length to 38mm led to reduction in the internal friction allowing satisfactory slump flow, filling capacity, and V-funnel flow time to be achieved with slight mixture modifications and no viscosity modifying admixtures were required. The addition of fibers did cause lower than acceptable L-Box test results where mixtures were made to change direction and flow between closely spaced bars. It was concluded that the slight increase in internal friction produced by the addition of fibers caused the low L-Box results and not any form of blockage. The plastic shrinkage test results showed that the addition of 0.40% fibers by volume led to as much as 70 % reduction in total crack area and up to 50% reduction in maximum crack width as compared to plain concrete. The results obtained from this research clearly shows that is it possible to develop highly crack resistant MSFRSCC mixtures for concrete structures.

Self-consolidating fiber-reinforced concrete (SCFRC) combines the benefits of self-consolidating concrete (SCC) in the fresh state and an enhanced performance of fiber reinforced concrete (FRC) in the hardened state. The application of SCC improves the efficiency at building sites, allows rationally producing prefabricated concrete elements and improves the working conditions, the quality and the aesthetical appearance of concrete structures. By adding fibers to SCC bar reinforcement can be replaced, crack widths reduced, the durability improved and the load bearing capacity of a structure increased. An extensive research study1 was carried out on the characteristics and the mix design of SCFRC that consisted of three parts: the fresh as well as the hardened state of SCFRC and the influence of the production process determined in three full-scale studies. This paper discusses two aspects of the mix design of SCFRC: the maximum fiber content and the required spacing of reinforcement at which blocking does not occur. Based on the analysis of experimental results mix design tools are proposed that allow predicting the maximum fiber content and the passing ability of SCFRC, which is essential information to obtain a homogeneous distribution of the fibers in a structure.

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.

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.

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.