| Abstract | One of the most common forms of deterioration of reinforced concrete structures is associated with the corrosion of reinforcement. The corrosion of reinforcement is mainly due to the ingress of oxygen, water, carbon dioxide, chloride, and other harmful substances. In this research, to study corrosion problem, the studies were divided into two parts. The effect of existing mechanical damage - cracks, sectional design - thickness of concrete cover, and material properties - types of blended powders of matrix, expansive agent and fly ash, on corrosion was investigated in first part. To achieve these objectives, experiments were conducted by exposing prepared specimens in outdoor condition. Due to the limitation of time, the accelerated approaches were adopted. Three accelerated techniques were the elimination of substance coating on the surface of steel, the use of 3% NaCl solution in the mix, and wetting and drying process utilization. In second part, field research of corrosion problem in Bangkok was performed to investigate and understand the present situation of existing structures in Bangkok and compare this situation to that at sea side location where information was obtained from previous research. The structures investigated in this study were bridges. The tested results in experimental part indicated that existing cracks remarkably reduce the resistance to corrosion in comparison with no crack case and thickness of concrete cover plays a significant role even if severe diffusion path - cracks- for harmful substances exist. The presence of severe cracks make more corrosion products of reinforcing steel bar than that of no cracks. The smaller thickness of concrete cover also produced higher degree of corrosion compared with higher thickness one. The effect of types of blend powders on corrosion could not be investigated that time because of short period when no corrosion takes place in no crack specimens. This effect will be examined one year later. Here, it must be noted that once mechanical damage, such as cracks due to external loading or drying shrinkage are introduced, the influence is much greater than irrelevant of that of material properties even if it influences corrosion under no crack situation. Further, it was reconfirmed that under chloride ion and crack existences severe corrosion can easily take place within one year exposure. For the research study of corrosion problem in Bangkok, two view points of deterioration cause were considered. In microscopic view point, the presence of aggressive substances in climate changed the material property of concrete thus resulting in deterioration of structures. In macroscopic point of view, the causes of deterioration of structures were the presence of cracks and small thickness of concrete cover. This small thickness one is reflected by the poor construction in which inspection during construction was performed carelessly. However as compared with structures at sea side location, structures in Bangkok was less severe and can be considered to be satisfying if good construction is expected with sufficient concrete coverage. |