INFLUENCE OF AR GLASS FIBERS ON THE CRACKING OF CONCRETE: ANALYSIS AT THE VERY EARLY AGE BY DIGITAL IMAGE CORRELATION

摘要

The aim of this work is to show the influence of Alkali-Resistant glass fibers on the cracking of concrete used for pavement applications at the early age and subjected to strong conditions of evaporation. This type of concrete, with a high cement content, is particularly sensitive to the plastic shrinkage. First, an experimental protocol was determined to guarantee the reproducibility of the phenomena (appearance of cracks) during the plastic phase. Then, an optical method without contact was used to measure the shrinkage on every point of the surface of a concrete's sample during the first 24 hours. This method consist of recording sample's pictures with a CCD camera. We calculate the displacement field between two pictures with numerical correlation techniques. Then we obtain strain fields and strain rate fields by temporal and spatial derivatives. We showed that this technique allows to measure the strains during the plastic phase, and therefore the shrinkage leading to early age cracking, and to follow the growing of cracks until hardening. This study showed that the incorporation of AR glass fibers contribute to limit the consequences of variations of composition of the concrete and the risk of cracking to this type of concrete at the early age.