The influence of fiber type and length on the cracking resistance, durability and pore structure of face slab concrete

The crack resistance and durability of face slab concrete are two important factors determining the normal operation and safety of concrete face rockfill dams (CFRDs). This paper investigates the influence of polypropylene (PP), polyvinyl alcohol (PVA) and polyacrylonitrile (PAN) fiber with two lengths (10 mm and 20 mm) on workability, strength, shrinkage behavior, cracking resistance and durability performance of face slab concrete. Besides, the parameters of the pores at multi-scales were investigated by a linear traverse method and the mercury intrusion porosimetry (MIP), respectively. The results in this study demonstrate that: (1) the efficiency in reducing the shrinkage and in enhancing the cracking resistance of face slab concrete follows the order of PVA > PAN > PP. In addition, both the impermeability and frost resistance of concrete can be improved by adding fibers, the efficiency is in the sequence: PAN > PVA > PP and PVA > PAN > PP, respectively. (2) increasing fiber length from 10 mm to 20 mm reduces the shrinkage by about 5.1%-7.0%, enhances the tensile strength (sigma) by about 7.9%-9.2% and declines the cracking temperature (Tc) by about 5.6-6.5., all of which could significantly improve the cracking resistance. Moreover, the increase in fiber length improves the frost resistance, but increases the relative permeability coefficient (Kr) by about 28%-47%. (3) The correlation analyses reveal that, the addition of PAN fibers produces a lower porosity, a lower fraction of large capillary pores as well as a lower hardened air content than the PVA and PP fibers at 28 days, thereby resulting in better impermeability of concrete. PVA fiber enhanced concrete gives the smallest spacing factor and the largest total number of air voids among all the fiber enhanced concretes, thus exhibiting the best frost resistance. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

This study demonstrates that PVA fibers are most effective in improving the cracking resistance and durability of face slab concrete. Increasing fiber length significantly enhances the cracking resistance and frost resistance of concrete.