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.