ABSTRACT
This chapter discusses the main sources of time-dependence and explores the available evidence of the influence of time on the fracture of concrete. It deals with the activation energy theory and the rate processes, which describes time- dependent fracture by means of a relationship between the crack growth rate and the stress intensity factor. The chapter discusses the applications of the rate theory to the fracture of concrete, including the effect of temperature and moisture content. It also presents an extension of the incurve concept to time-dependent processes. The chapter briefly introduces linear viscoelastic fracture mechanics. It describes the rate-dependent R-curve model with creep developed for concrete by Z. P. Bazant and M. Jirasek, which explains many of the experimental aspects of the fracture of concrete. Fatigue fracture has been studied to a great depth in the field of metals and composites, since it plays an essential role in the safety and lifetime of machines, aircraft, and ships.
