Flexural and Tensile Characteristics of Micro Fiber-Reinforced Very High Strength Concrete Thin Panels

Abstract

The purpose of this research was to experimentally characterize the flexural and tensile characteristics of fiber-reinforced Very High-Strength Concrete (VHSC) panels. The panels were made with a unique mix of cementitous materials achieving compressive strength of 26,000 psi (180 MPa) or greater. VHSC panels were reinforced with polypropylene fibers of 1 inch (25.4 mm) in length and Polyvinyl alcohol (PVA) micro-fibers of ½ inch length, incorporated at 1.5% by volume. For the flexural behavior, 17×2×¾ inch flat panels were tested under third-point loading tests, while the direct tension experiments were tested on 10×3×½ inch tension panels under a direct tensile load. Flexural tests were conducted on three panels of plain VHSC, three panels of VHSC reinforced with polypropylene fibers and three panels of VHSC reinforced with ½ inch micro-fibers. Similar testing program was used to conduct the direct tension tests. Also, compression test conducted on 2×2×2 inch cubes and compressive test conducted on 4 inch by 8 inch cylinders test were used to establish compressive strength and modulus of elasticity respectively. Results show that the compressive strength, tensile strength and fracture toughness of the VHSC panels were much greater than those normally obtained by typical concrete material. The presence of fibers increases the toughness of VHSC specimens between 80 and 190% and increases the tensile strength by 23 to 47%. The modulus of elasticity and Poisson’s ratio recorded herein were determined according to ASTM C 469-02. Laboratory experiments on flexural and tensile properties of thin, very high-strength, fiber reinforced concrete panels, were used to study the material and characterize the panels’ reaction to load. Parameters such as compressive strength, tensile strength, toughness, elastic modulus, Poisson’s ratio and first-crack strength were determined and may be considered for potential use as design parameters in future material improvements

Fracture behavior of polymeric fiber reinforced lightweight structural concrete

“…A number of studies were carried out in order to evaluate the mechanical properties of the produced composites [4][5][6][7][8] , and the results indicated the viability of using such fibers as reinforcing elements. Despite a tolerable degradation in the compressive strength, flexural strength and fracture toughness were significantly enhanced due to the presence of fibers in the cementitious matrix, consistent with experimental data reported by Abu-Lebdeh et al 3 . It is to be noted, though, that the susceptibility of natural fibers to degradation, due to ambient and biological factors, requires appropriate surface treatment in order to improve their durability.…”

“…The sand used as fine aggregate had a fineness modulus of about 3.33, a maximum particle diameter of 2.38 mm and an apparent density of 1.6 g/cm 3 . As to the polypropylene fibers, these were 100 mm in diameter and about 50 mm in length, with a corresponding aspect ratio of 500 and density of 0.91 g/cm 3 (in fact, a mass of one kg was found to contain about 2.8 × 10 6 fibers). Its modulus of elasticity is situated at about 4 GPa.…”

“…The fiber reinforced beams, on the other hand, also exhibit a second stage corresponding to transition into a ductile response accompanied by an increase in the applied load, indicating that the incorporation of fibers is beneficial to the flexural strength and ductility and, therefore, to toughness of the concrete. This is attributed to strengthening and energy absorbing mechanisms [1][2][3] invoked by the flexural (tensile) stress acting in both precracked and uncracked bend loaded beams.…”

“…Without the addition of fibers, the concrete behaved, essentially, in a linear elastic and brittle mode, with a complete loss of tensile stress upon first cracking. The presence of the short randomly distributed fibers had a beneficial effect on the post-crack behavior, promoting the concrete's ductility and toughness 3 . Observing the three point bend loading curves, three distinct phases of flexural response could be distinguished: -initial response characterized by a linear loaddeflection behavior, presumably up to first crack load; -second stage of the load-deflection curve corresponding to sharp transition into a ductile response and progressing to the ultimate load; -third stage with the composite failing abruptly with the development of a single macrocrack and a swift loss of load resistance / or with a small residual load carrying capacity 3 .…”

“…Whereas the addition of the steel fibers generally contributed to the energy absorbing mechanism (bridging action), the nonmetallic fibers resulted in delaying microcrack formation 1 . In a recent study 3 , very high strength concrete panels had their tensile strength and fracture toughness significantly increased by the incorporation of polypropylene fibers at 1.5% by volume. Without the addition of fibers, the concrete behaved, essentially, in a linear elastic and brittle mode, with a complete loss of tensile stress upon first cracking.…”