International Concrete Abstracts Portal

Paper presents the results of an experimental investigation on the behavior of slurry-infiltrated fiber concrete (SIFCON) subjected to flexure, shear, and axial tensile loading. More emphasis was placed on the flexural behavior in which the specimens were subjected to static and high-amplitude cyclic loading. Four fiber lengths, namely, 30, 40, 50, and 60 mm, and four volume contents ranging from 4 to 12 percent were used. Fibers with hooked ends were used for the entire investigation. Effect of the addition of silica fume and sand to cement slurry was investigated by using a selective group of specimens made with 8 percent fiber content. Freeze-thaw studies were also conducted using prisms that had 8 percent fibers. The behavior in shear was studied using direct shear specimens. Properties in axial tension were investigated using four fiber contents of 50 mm long fibers. The results indicate that strengths of up to 10,000 psi (68.9 MPa), 4000 psi (27.6 MPa), and 2000 psi (13.8 MPa) can be obtained in flexure, direct shear, and axial tension, respectively. The composite is extremely ductile in all three modes of loading. Based on the tests conducted in flexure, addition of silica fume increases the strength. Sand can be added to the slurry without reducing the strength up to a certain cement-sand ratio. The ductility characteristics are not affected by the addition of either sand or silica fume.

To manufacture load-bearing structures of thin-walled concrete, a new production method called EKEBRO fiber shotcrete was developed. The essential part in the technology is a patented spray gun. Steel wire (0.5 mm), concrete, and compressed air are fed into the spray gun. A cutting wheel cuts the wire into fibers of the required length and shoots these in a stabilized direction on the form or surface together with the concrete. Through this method, a good distribution of steel fibers in the product is achieved, and long fibers can be utilized. Spraying with a variating steel fiber content is also possible. The method is used presently in Sweden for the production of balconies for apartment buildings and, further, for the production of various other products. The technique is also used in traditional shotcreting work, such as repair of deteriorated structures.

Results of an experimental investigation of the properties of steel fiber reinforced structural lightweight concrete are presented. The concrete was proportioned to obtain a compressive strength of about 6000 psi (41.3 Mpa). The targeted values for slump and air content were 4 to 8 in. (100 to 200 mm) and 8 percent, respectively. Collated fibers 30 mm long with hooked ends were used for the entire investigation. The fresh concrete was tested for temperature, slump, V-B time, flow table spread, air content, and unit weight. The hardened concrete was tested for dry unit weight, compressive strength, flexural strength, splitting tensile strength, and shrinkage. In addition to these results, a comparative evaluation of normal-weight and lightweight fiber reinforced concretes is also presented. Study results show that highly workable, high-strength, lightweight fiber reinforced concrete can be produced successfully. The lightweight concrete has as much energy absorption capacity as the normal-weight concrete.

In multistory framed structures, three kinds of connections exist, namely, cross-type, tee-type, and knee-type. Experimental investigations were made to study the behavior of 50 such beam-column connections of conventional and steel fiber concrete (SFC) when tested under static, as well as slow-cycle fatigue, loading. In all, 10 cross-type specimens of full-scale two-span beam with column stub were tested. Four cross-type connections were cast with conventional concrete, two with steel fibrous concrete in the entire length and four with SFC in the joint region only. The test results showed that SFC improved the ductility at the joint region, increased load-carrying capacity, decreased crack width, eliminated shear reinforcement, and overcame the problem of spalling of concrete in the joint region. The testing work also included 20 tee-type and 20 knee-type connections with 12 of each tested under static load and eight under slow-cycle fatigue load. The percentage was kept as 0.0, 0.6, 0.8, and 1.0 of concrete volume. Instrumentation was done to measure deflections, rotations, strains, and crack widths.

Tests were made on 92 knee-type steel fiber reinforced concrete (SFRC) beam-column connections to determine the effect of steel fibers on strength and behavior. Both beam and column had overall sections of 4 x 4 in. (101.6 x 101.6 mm) and length of 16 in. (406.4 mm) each. The column had main reinforcement comprised of two bars of «-in. (12.0 mm) diameter deformed steel bars having yield strength of 67.5 ksi (4745 kgf/cmý) near the outside face and two bars of ¬-in. (6.0-mm) diameter of deformed steel near the inside face of the column. The column had 3/16-in. (5.0-mm) diameter ties of plain mild steel at 3 in. (76.5 mm) center to center. The two bars of 1/2-in. (12.0-mm) diameter near the outside face of the column were continued into the top of the beam to provide main steel. The variables were M/P ratio (moment to axial load) type percentage and aspect ratio (length to diameter) of the fibers. Brass-coated high-strength steel plain fibers of size 1.0 x .01 in. (25.4 x 0.254 mm), « x 0.006 in. (12.7 x 0.152 mm), 1.0 x 0.016 in. (25.4 x 0.406 mm), and mild steel fibers of 0.011-in. (0.282-mm) diameter having aspect ratio of 10, 25, 50, 75, and 100 were used. The percentage of fibers (by volume of concrete) varied from 0.5 to 2.0. Connections having conventional reinforcement only were also tested. The test results indicated that steel fiber reinforced concrete is very effective in increasing ductility and crack resistance in the connection region. Ultimate rotation of SFRC connections was six to nine times that of conventional connections. There was an increase in moment capacity of 15 to 30 percent with increase in fibers from 0.5 to 2.0 percent by volume. Moment capacity increased by about 50 percent when the aspect ratio of the fibers was increased from 10 to 100.