Strength and flexural toughness of hybrid fibre reinforced fly ash based concrete

To overcome concrete brittleness and to provide toughness, fibre reinforcement is commonly utilized. Fibre reinforcement to concrete in the form of hybrid fibre is a new concept to achieve individual fibre benefits. In this paper, the effect of polypropylene fibre (PF) and steel fibre (SF) either individually or with different combinations at 1% fibre volume fraction on the strength, flexural toughness, and Ultrasonic pulse velocity (UPV) value of FIBRE-reinforced fly ash (FA) based concrete has been presented. For this purpose, one control mix having 25% FA and 0% fibre and five mixes with different hybrid fibre combinations of 1%PF-0%SF, 0.75%PF-0.25%SF%, 0.50%PF-0.50%SF, 0.25%PF-0.75%SF, and 0%PF-1%SF were cast. ASTM C 1609 method was utilized to evaluate the flexural toughness. Experimental results have shown an improvement in all the above-said properties (expect UPV) by the addition of fibre, but improvement is more significant in mixes with a higher percentage of SF when compared with mixes at a higher percentage of PF. Mix with a hybrid fibre combination of 0.25% PF and 0.75% SF gave the best result among all the fibre-reinforced fly ash-based mixes.

An Experimental Investigation on the Mechanical Properties including Strength and Flexural Toughness of Mortar Reinforced with Steel-Carbon Hybrid Fibers

This paper presents the results of an experimental investigation conducted to evaluate the mechanical properties, including strength and flexural toughness of hybrid fiber-reinforced mortar (FRM) containing various combinations of steel and carbon fibers with different material characteristics. The mortar specimens were mixed with steel and carbon fibers in the mix proportions of 100 + 0%, 75 + 25%, 50 + 50%, 25 + 75%, and 0 + 100% by volume at a total volume fraction of 1.0%. The flexural performance (flexural strength and toughness) of the mortar specimens was obtained using the third-point loading arrangement stipulated in the test methods of ASTM C 1609/C 1609/M and KS F 2566. In addition, compressive strength was also measured according to the KS F ISO 679 test method. Their mechanical properties were examined and compared with plain mortar (PM) at the age of 28 days. The test results showed the highest compressive and flexural strengths in the hybrid FRM reinforced with 75% steel fibers + 25% carbon fibers, confirming the synergistic reinforcing effect of the steel and carbon hybrid fibers. However, the hybrid FRM reinforced with 50% steel fibers + 50% carbon fibers has obtained slightly low flexural strength but owned the highest flexural toughness and hence can be judged as the most appropriate combination to be employed in hybrid FRM to improve the flexural toughness. Moreover, the fractured FRM surface was also observed via scanning electron microscopy (SEM) after platinum coating in vacuum. These results would be of great help in establishing the microstructural mechanism of hybrid reinforcing fibers in the cement matrix.

MECHANICAL PROPERTIES OF RECYCLED COARSE AGGREGATE CONCRETE REINFORCED WITH STEEL FIBERS

This paper presents the combined influence of natural aggregates (NA) replacement with recycled concrete aggregates (RCA) and incorporating steel fiber reinforcement on the mechanical properties of normal-strength (30 MPa) concrete mixes. Hooked-end steel fibers were added in a 2% volumetric fraction to promote 100% RCA replacement. Fine aggregates were in the form of locally-abundant desert dune sand. Mechanical properties of 28-day concrete samples were assessed, including compression strength, tensile splitting strength, elastic modulus, flexural stress, and flexural toughness. For plain concrete mixes, the replacement of NA by RCA resulted in 18, 27, and 5% reductions in the respective design compression strength, elastic modulus, and tensile splitting strength. Nevertheless, the addition of steel fibers could restore the aforementioned properties by up to 90, 77, and 164%. Compared to the control mix made with NA, the flexural strength of the plain RCA-based concrete mix decreased by 33%, while the flexural toughness increased by 100%. In turn, the corresponding flexural properties of RCA concrete mix reinforced with steel fibers were 2 and 56 times those of the control made with NA. Findings provide evidence of the ability to produce concrete made with 100% RCA and reinforced with steel fibers with comparable compression properties and improved tensile and flexural performance compared to those of NA-based concrete.