Title: Synthetic Fibers and Rheology Modifier: Effects on Settlement Cracking

Author(s): Osama Al-Qassag, Ryan Brettmann, David Darwin, Matthew O’Reilly, and Rouzbeh Khajehdehi

Publication: Materials Journal

Volume: 119

Issue: 1

Appears on pages(s): 289-296

Keywords: crack-reducing technologies; fibers; low cover; rheologymodifying admixture; settlement cracking; slump; testing; viscositymodifying admixture (VMA)

DOI: 10.14359/51734302

Date: 1/1/2022

Abstract:
A test procedure was developed to evaluate the effect of different techniques to limit settlement cracking over reinforcing steel with low concrete cover. Various specimen configurations and methods of finishing and curing were investigated. It was found that a clear cover of 1-1/8 in. (29 mm) over a No. 6 (No. 19) bar and covering the specimens after placement with sloped hard plastic enclosed in plastic sheeting provided a suitable method for obtaining clearly visible settlement cracks for concrete with slumps ranging from under 2 in. (50 mm) to over 8 in. (205 mm). The test specimen was then used to evaluate the effectiveness of a rheology-modifying admixture and four types of synthetic fibers on settlement cracking. Eighty-eight concrete batches were tested for mixtures with a cement paste (cement and water) content of 27 percent by volume and a water-cement ratio (w/c) of 0.45. The results show that the addition of the rheology-modifying admixture or fibers greatly reduces settlement cracking over reinforcing steel with low concrete cover.