Durability assessment of concrete materials under the effect of shrinkage-induced damage and benzotriazole corrosion protection system.

摘要

During their service life, concrete structures are typically subjected to several physical and chemical degradation factors due to structure-environment interaction. When these factors are combined with the mechanical loads, they accelerate the aging and deterioration of concrete materials and consequently impair the durability of concrete structures and shorten their service live. This research is divided in two parts and focuses on two processes related to the durability of concrete materials. The first is the deterioration of concrete due to drying shrinkage and the second process is the corrosion of steel reinforcement in concrete.; Concrete structures undergo drying shrinkage within their service life due the change in water content after exposure to the atmosphere. If they are restrained, then internal stresses develop and may cause damage and cracking in those structures. At the same time, damage in the concrete accelerates the drying process by modifying the moisture transport parameters. Also, damage caused by drying shrinkage leads to eventual deficiency of buildings and infrastructures over time because this damage permits the ingress of harmful materials into the concrete. The principal objective of the first part was to develop experimental and numerical modeling approaches for studying the interaction between moisture diffusion and shrinkage-induced damage of concrete. This was accomplished through: (a) development of numerical models and computer simulations for the performance of concrete structures under different exposure drying conditions and (b) development of experimental methods to quantify the concrete damage and its relation with degree of drying. The numerical simulation showed reasonable predictions of the drying process and damage propagation in concrete when compared with experimental data. The experimental results show that the drying shrinkage of restrained slabs develops localized cracks orientated perpendicular to the drying surface and extending through the whole depth of the slab.; Corrosion of steel rebars embedded in concrete structures is also a principal cause for concrete deterioration. Active corrosion of reinforcing rebars can arise in conjunction with two specific sets of conditions: carbonation or chloride intrusion (or a combination of both). The goal of the second part of this research was to design and evaluate the effectiveness of corrosion protection systems using benzotriazole (BTA) derivatives. In addition, the protection mechanisms of benzotriazole derivatives and film formation on steel surfaces were studied, and the effect of loading-induced damage on reinforcing steel corrosion was investigated. Corrosion tests were done on two types of samples: reinforced concrete beams and steel electrodes in simulated concrete pore (SCP) solutions. The results showed that BTA forms a coating film on the steel surface, and it provides a good protection for the reinforcing steel where the corrosion rate decreases and the corrosion resistance increases.