Title: Strategies to Mitigate Cracking of Self-Consolidating Concrete
Author(s): Fodhil Kassimi and Kamal H. Khayat
Publication: Materials Journal
Appears on pages(s): 73-83
Keywords: cracking; expansion agent; fibers; restrained shrinkage; retrofitting; self-consolidating concrete; shrinkage-reducing admixture; time-to-cracking
The efficiency of various strategies to reduce cracking of self consolidating, fiber-reinforced self-consolidating, and superworkable 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 (Vf), respectively. Fiber-reinforced self-consolidating mortar (FR-SCM) with 0.8% and 1.4% Vf 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 (tcr) in the restrained shrinkage ring test of 36 days (low cracking potential). Such concrete exhibited the narrowest crack width (wcr) of 85 μm (0.0033 in.), which was comparable to that of FR-CVC (80 μm [0.0031 in.]). For the other mixtures, tcr values ranged between 1 and 23 days, and wcr values between 90 and 210 μm (0.0034 and 0.0083 in.); the highest value was 285 μm (0.0111 in.) obtained for the SCC without fibers, EA, and SA. Empirical models were proposed to predict tcr 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.