Fiber–matrix interaction at early ages of concrete with short fibers

The inclusion of small amounts of short fibers has demonstrated to be an effective solution to control cracking due to drying shrinkage of concretes at early ages. The key point of fiber effectiveness is their capacity to sew the crack sides, preventing crack opening, because cracking of concrete matrix induces fiber actuation. In this paper, fiber–matrix interaction is analyzed considering different amounts (from 600 to 1200 g/m3) and lengths (6, 12 and 18 mm) of alkali-resistant (AR) glass fibers and fiber coating effect. The combination of experimental results previously published and analyses with simple FE models allows for better understanding of early age concrete behavior. As concrete mechanical capacity develops with age, while fibers have full properties before being included in concrete matrix, the interphase between matrix and fibers evolves during setting and hardening, and affects cracking control effectiveness, due to stresses induced by fibers into the matrix during concrete hydration.