Flexural response characteristics of ultra‐high performance concrete made with steel microfibers and macrofibers

Abstract

Ultra‐high performance concrete (UHPC) is increasingly used for various engineering applications, owing to its superior strength properties. Such properties, however, can be accompanied by workability issues, especially if the dosage of steel fibers is significantly increased. As a potential solution, this study explored the use of a combination of steel microfibers and macrofibers through a holistic experimental testing program. This was to understand the effects of steel fiber combinations on the workability and flexural strength of various UHPC mixtures. The microfibers were investigated for five different dosages from 1.0% to 3.0% (with an increment of 0.5%). In parallel, two mixtures were prepared with a 2.0% dosage of macrofibers in the form of twisted wire and hooked fibers. At the next stage, six additional mixtures were prepared with a combination of microfibers and macrofibers of various dosages. Further to the measurements extracted from the workability and flexural strength tests, digital image correlation (DIC) analyses were employed to obtain firsthand information about the widths and depths of cracks observed in the flexural specimens tested under an increasing load. The outcome of this study showed how a combination of microfibers and macrofibers can contribute to improving the flexural response characteristics of UHPC, especially without having to increase the dosage of steel fibers to the ranges that can adversely affect the mixture's workability.

Mechanical properties of hybrid fiber‐reinforced concretes made with low dosages of synthetic fibers

“…This is critical, especially for plastic shrinkage, during which concrete is still in the fresh state and has not gained an adequate strength 11–16 . On the other hand, macrofibers are most beneficial in enhancing the concrete's postpeak strength properties through bridging macrocracks and enabling the concrete matrix to offer enhanced ductility and impact resistance 17–24 . Given the complementary contributions of micro and macrofibers to concrete, a transition to hybrid fiber‐reinforced concrete (FRC) mixtures, which contain both micro and macrofibers, has received growing attention 25–28 …”

“…[11][12][13][14][15][16] On the other hand, macrofibers are most beneficial in enhancing the concrete's postpeak strength properties through bridging macrocracks and enabling the concrete matrix to offer enhanced ductility and impact resistance. [17][18][19][20][21][22][23][24] Given the complementary contributions of micro and macrofibers to concrete, a transition to hybrid fiberreinforced concrete (FRC) mixtures, which contain both micro and macrofibers, has received growing attention. [25][26][27][28] Focusing on the development of hybrid FRC with synthetic fibers, Ahmed and Mihashi 29 investigated a set of FRC mixtures that contained micro and macro polyvinyl alcohol (PVA) fibers with a dosage from 1.0% to as high as 3.0% of the concrete's volume.…”

Effect of fiber content and stress–strength ratio on the creep of basalt fiber–reinforced alkali‐activated slag concrete

“…Furthermore, the addition of fiber can significantly improve the flexural strength of concrete. 22,23 Researchers have also added polypropylene (PP) fiber to concrete to study the creep properties of concrete. 24,25 Haddad and Smadi 25 demonstrated that PP fiber was superior to steel fiber because of the lower fiber content required and lower cost.…”

“…They also found that the inhibitory effect of fiber on creep was strengthened by the increase in fiber content. Furthermore, the addition of fiber can significantly improve the flexural strength of concrete 22,23 . Researchers have also added polypropylene (PP) fiber to concrete to study the creep properties of concrete 24,25 .…”

Experimental and numerical study on T‐Shaped UHPFRC beams with high‐strength reinforcement

“…Ultra-high performance fiber-reinforced concrete (UHPFRC) consists of ultra-fine active powder, cement, admixture, superplasticizer, and steel fiber. Compared with conventional concrete, studies [1][2][3][4][5][6][7] show that UHPFRC has higher strength, better ductility and durability, and higher resistance under special loads, such as impact loads and fatigue loads. UHPFRC was initially applied in reinforced concrete (RC) structures as a repair technique.…”