Strategies to Mitigate Cracking of Self-Consolidating Concrete

The efficiency of various strategies to reduce cracking of self-consolidating, fiber-reinforced self-consolidating, and super-workable concretes (SCC, FR-SCC, and FR-SWC, respectively) designated for repair applications is discussed. The FR-SCC and FR-SWC mixtures were prepared with 0.5% and 0.75% fiber volume (V-f), respectively. Fiber-reinforced self-consolidating mortar (FR-SCM) with 0.8% and 1.4% V-f were also investigated. Of particular interest is the resistance to restrained shrinkage. In addition to the use of fibers, shrinkage mitigation measures included the use of shrinkage-reducing admixture (SA) and/or a calcium oxide-based expansive agent (EA). In total, 18 mixtures were investigated. Mono- and multifilament synthetic and steel fibers were employed. A fiber-reinforced conventional vibrated concrete (FR-CVC) made with 0.5% steel fibers was prepared as a reference mixture. For the self-consolidating mixtures, the highest resistance to restrained cracking was obtained with the FR-SCC made with steel fibers and EA that exhibited a time-to-cracking (t(cr)) in the restrained shrinkage ring test of 36 days (low cracking potential). Such concrete exhibited the narrowest crack width (w(cr)) of 85 mu m (0.0033 in.), which was comparable to that of FR-CVC (80 mu m [0.0031 in.]). For the other mixtures, t(cr) values ranged between 1 and 23 days, and w(cr) values between 90 and 210 mu m (0.0034 and 0.0083 in.); the highest value was 285 mu m (0.0111 in.) obtained for the SCC without fibers, EA, and SA. Empirical models were proposed to predict t(cr) and cracking potential as a function of elastic modulus and drying (and autogenous) shrinkage. The best relative overall performance was obtained for FR-SCC made with steel fibers and EA or SA, followed by FR-SCC made with synthetic fibers, then SCC and FR-SCM.