Developing a Test Procedure to Evaluate Settlement Cracking Performance

Abstract

A test procedure was developed to evaluate settlement cracking in concrete. The procedure was used to evaluate the effects of slump and the addition of either Acti-Gel® 208 or FORTA-FERRO® fibers on settlement cracking. The specimens consisted of 12×12×8 in. concrete blocks with No. 6 bars at 1.5 in. of cover to the center of the bar (nominal clear cover of 11/8 in.). Various methods of finishing and curing the specimens were investigated. It was found that covering the specimens with sloped hard plastic enclosed in plastic sheeting was a suitable method for obtaining unblemished specimens with clearly visible settlement cracks. The procedure was used to test 38 concrete mixtures with slumps ranging from ½ to 9 in. Of the 38 mixtures, 24 were control mixtures, 8 contained 2¼-in. FORTA-FERRO® fibers, and 6 contained Acti-Gel® 208, a rheology modifier and anti-settling agent. Average crack length, normalized to the length of the bar, was calculated for each mixture. Although there is significant scatter to the data, increasing slump increases the amount of settlement cracking. Initial results suggest that the addition of Acti-Gel® 208 to concrete decreases the amount of settlement cracking. Initial results also suggest that the addition of FORTA-FERRO® fibers to concrete decreases the amount of settlement cracking. There is a significant amount of scatter in the data for mixtures with similar slumps.