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Cementitious materials are known to be sensitive to cracking at early ages. During the first days which follow the contact between water and cement, the system is continuously evolving, as its mechanical characteristics follow a rapid rate of change and the material is prone to cracking. One of the parameters that highly influence the behavior of the material at early ages is the Young's modulus. Analytical calculations, based on existing homogenization models and finite element calculations, applied on a discrete generated microstructure, are first considered in order to predict the elastic properties of the material. As long as the cohesive role played by the hydrates is not taken into account, results at early age remain inaccurate, especially for low watercement ratios. The need of modeling an intrinsic characteristic of cementitious materials setting arises. An approach, based on percolation and on the so-called burning algorithm, which takes into account explicitly the bonding role of hydrates and reveals a degree of hydration threshold below which the rigidity of the material is negligible, is therefore proposed. The evolution of the elastic characteristics is obtained by applying the previous computation methods to the percolation cluster given by the burning algorithm

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Abstract. The objective of the paper is to analyze the effect of substrate roughness and superficial microcraking upon adhesion of repair systems using concrete surface engineering approach. The results presented in this paper have been obtained within the framework of research projects performed to develop a better understanding of the factors affecting the adhesion of repair materials through a surface engineering approach. Based on the results of investigations, the authors showed that the durability and quality of concrete repairs depend to a large degree on the characteristics of the substrate. Mechanical preparation and profiling of the concrete surface to be repaired has to be balanced with potential co-lateral effects such as superficial cracking, too often induced as a result of inappropriate concrete removal method selection, and the loss of benefits due to better mechanical anchorage. The results obtained confirm also that Concrete Surface Engineering, as a scientific concept, will definitely contribute to shed more light on how to optimize repair bond, taking into account interactions between the materials at different observation scales.