Defect in reinforce concrete structures has been an issue bothering the civil engineers and all those involved in the construction industry. Therefore, in the course of writing this project, different phenomenon were adopted to analyze the causes of defects, among are, an experiment carried out with the aid of washed and unwashed aggregate to understand the behavior different of concrete strength in them, which further proved that the washed aggregate developed the greatest strength than the unwashed aggregate that in the case of unwashed aggregate presence of deleterious materials and debris led to developed lesser strength after setting. The cases of failed building at sagbama, Bayelsa State, during site visitation it was discovered that two story building were abandoned in sagbamaBayelsa State as a result of deflection, swelling, deformation and as well vibrating. And with information gotten from the above failed building, it was due to inadequate reinforcement, inadequate subsoil investigation, lack of competent supervision etc where the causes of the failed building. The controls of defects in the cases of the phenomenon mentioned above were discussed in the project.