Title: Control of Plastic Shrinkage Cracking with Specialty Cellulose Fibers

Author(s): Parviz Soroushian and Siavosh Ravanbakhsh

Publication: Materials Journal

Volume: 95

Issue: 4

Appears on pages(s): 429-435

Keywords: cellulose fibers; fiber reinforcement; plastic shrinkage; restrained shrinkage cracking;

DOI: 10.14359/385

Date: 7/1/1998

Abstract:
Specialty cellulose fibers processed for the reinforcement of concrete offer relatively high levels of elastic modulus and bond strength. The hydrophilic surfaces of cellulose fibers facilitate their dispersion and bonding in concrete. Cellulose fibers have small effective diameters that are comparable to the cement particle size and, thus, promote close packing and development of a dense bulk and interface microstructure in the matrix. The relatively high surface area and the close spacing of cellulose fibers when combined with their desirable mechanical characteristics make cellulose fibers quite effective in the suppression and stabilization of microcracks in the concrete matrix. The investigation reported herein concerns the effects of specialty cellulose fibers on the restrained plastic shrinkage cracking of conventional and high-performance concrete. Cellulose fibers were used here at 0.06 percent volume fraction, which is equivalent to a fiber content of 0.9 kg/m3 (1.5 lb/yd3). Plastic shrinkage cracks occur when the early-age shrinkage movements (prior to final set) are restrained; this commonly occurs on the surfaces of concrete flatwork in windy, hot, and dry conditions that promote rapid evaporation. Under such conditions, a moisture gradient develops in concrete that produces internal restraint against shrinkage movements of the surface layers. In our experimental program on restrained shrinkage cracking of conventional and high-performance concrete, noting that plastic shrinkage cracking test results show an inherently high variability, statistical analysis of replicated test results confirmed that cellulose fibers are effective in reducing the plastic shrinkage cracking of conventional and high-performance concrete. Cellulose fibers had statistically comparable effects on plastic shrinkage cracking of conventional and high-performance concrete.