Early-Age Cracking Resistance of Multiscale Fiber-Reinforced Concrete with Steel Fiber, Sisal Fiber, and Nanofibrillated Cellulose

In order to solve the cracking issue of concrete under external restraint conditions, the common method is to add fibers (steel fiber, polypropylene fiber, etc.) to concrete. However, steel fiber is heavy and costly. In this paper, a slab test was carried out, and the cracking control effect of a macro-nano multiscale cracking prevention system formed by using natural green sisal fiber instead of steel fiber and nanofibrillated cellulose (NFC) on concrete is studied. A total of 14 test groups were set up, including the test groups of a single sisal fiber and single steel fiber dosage; sisal fiber combined with steel fiber with equal volume; a sisal fiber and nanofibrillated cellulose (NFC) combination; and a sisal fiber and steel fiber and nanofibrillated cellulose (NFC) hybrid combination. The early-age cracking behavior of concrete of the preceding groups were observed. The results show that the use of sisal fiber with 0.4% volume content improves the early-age cracking of concrete to the same extent as the use of steel fiber with 1% volume content. Compared with the addition of steel fiber alone, sisal fiber replacing steel fiber with equal volume can not only significantly improve the cracking resistance of concrete and reduce its cost and weight, but also protect the environment. Last but not least, results indicate that sisal fiber and nanofibrillated cellulose (NFC) also play a good synergistic role in delaying and controlling the cracking development of concrete. The macro-nano multiscale fiber by steel fiber, sisal fiber, and nanofibrillated cellulose reinforced-concrete cracking resistance mode is achieved.