Fracture mechanics of earlyage concrete

In this paper, the fracture mechanics of concrete structures is first reviewed. This clearly dem- onstrates that, despite the successful application of fracture mechanics to study the fracture behavior of ma- ture concrete, its application to the cracking of very early-age concrete (i.e. within several hours after mixing) is still in its infancy, with very limited literature available. This is believed principally to be the result of diffi- culties that arise in the experimental determination of the properties of extremely fragile concrete at very early ages. In a recent research at the University of Queensland, a test apparatus and experimental procedures have been developed that enable the complete tensile stress-displacement behavior of concrete specimens at very early ages to be captured reliably. Based on the data obtained, the paper shows that current models for the stress-separation relationship of mature concrete may not apply for concrete at very early ages. Revised mathematical models for the stress-separation relationship of early-age concrete are proposed. 1 REVIEW OF FRACTURE MECHANICS OF ing (Fig. 1). In ductile-brittle materials, the fracture CONCRETE STRUCTURES process zone (FPZ), which is the zone in which the material undergoes softening damage, is quite small. The risk of failure due to the growth of cracks can be In quasi-brittle materials (such as mature concrete, treated using the science known as fracture mechan- rock, and ceramics), however, plastic flow is almost ics, which arose initially from the work of Griffith nonexistent and the FPZ fills almost entirely the (1920) on the fracture of brittle materials such as nonlinear zone (Fig. 1). It has been suggested that glass.