Microstructure of damages in the concrete composites with cement matrixes
Grzegorz L. Golewski Politechnika Lubelska, Wydział Inżynierii Budowlanej i Sanitarnej, ul. Nadbystrzycka 40, 20-618 Lublin, Poland
Quarterly No. 1, 2008 pages 93-98
DOI:
keywords: concrete composite, brittleness of concrete, straight crack, wing crack, critical stress, nanomodification
abstract The structure of the concrete composites with cement matrixes has been characterized in the article in the context of their susceptibility to brittle damages. The structure of the interfacial transition zone between the matrix and inclusions has been described. As the weakest place in the concrete, the interfacial transition zone is of decisive importance for the process of defect initiation in the concrete structure. Basic causes of defect development in concrete have been presented as well as the places of defect occurrence have been described. The analysis concerning scan images (images of destructed composites) proves that the development of straight and wing-type cracks (progressing in accordance with the increase of external load) is the decisive factor for destruction of material. The stages of cracks progression have been combined with the levels of critical stresses and Straight cracks occur in the composite when the first stress level is exceeded while the increase of wing-type cracks takes place when critical stresses reach the level of . Further development of material defects progresses in an uncontrolled manner and consequently leads to rapid destruction of material even in case of a small load increase. Development of microcracks has a decisive influence on final macroscopic deformations of concrete. In order to prevent occurrence of defects in the composite structure, it is possible to employ nanotechnology in the concrete production technology. For this purpose, non-reactive or reactive nanomolecules (e.g. in the form of fly ash, silica fume and microfibres, precipitated silica or nanosilica) are introduced to the concrete microstructure. The concept of self-repairing concrete can be also applied that consists in introducing microcapsules filled with epoxide resin into the initial structure of the composite. Bacillus Pasteurii soil bacteria can be used as another type of active nanomodifier.