ACI 231R-10 - Report on Early-Age Cracking: Causes, by ACI


Early-age cracking is a problem for the concrete undefined. fabrics choice, environmental stipulations, and box practices all have huge effect at the propensity for early-age cracking to ensue. This rfile makes a speciality of thermal- and moisture-related deformations; either are materials-related and give a contribution to early-age cracking. The record presents special reports at the explanations of deformation and cracking, try tools for assessing shrinkage and thermal deformation homes, and mitigation innovations for decreasing early-age cracking.

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A high rate of evaporation causes a steep gradient of the capillary pressure at the surface of the mortar or concrete; therefore, a high tensile stress at the surface would induce plastic shrinkage cracks. The lower rate of evaporation obtained by addition of SRA should therefore reduce the tensile stress at the surface and ultimately reduce the probability of plastic shrinkage cracking, as shown in Fig. 8. 3 Influence of SRA on drying shrinkage—Concrete is generally observed to shrink (that is, reduce its volume) in response to the loss of water that is held in the pore space of the concrete.

21—Autogenous shrinkage (– is shrinkage) for mortars containing different internal curing agents, all cured at 86°F (30°C) (Geiker et al. 2004). *SF (silica fume, slag, and fly ash), internal curing results in approximately a 10% strength gain (relative to the control) at 28 days and beyond. 3 and were cured under sealed conditions at 77°F (25°C) (Bentz 2007). 08 extra mass units of water per unit mass of cement were added via the saturated lightweight aggregate. 2. Testing laboratory results have also indicated that earlyage strength gains may be achieved by the incorporation of internal curing into high-performance concrete mixtures.

Bentur et al. (2001) observed similar behavior, as shown in Fig. 12(b), although less stress reduction was observed. Delays or prevention in the age of cracking in ring specimens has also been reported for a wide range of concrete mixtures (Shah et al. 1992; Nmai et al. 1998; Weiss 1999; See et al. 2003; Folliard and Berke 1997; Weiss et al. 1998a). Weiss et al. (1998b) demonstrated that the results of SRA performance from the restrained ring test could be extended to slab geome- 231R-33 Fig. 10—(a) Influence of SRA on shrinkage in typical normal-strength concrete (Weiss 1999); and (b) influence of SRA on drying shrinkage with different w/cm (Weiss 1997).

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