Using the Response Surface Method to Optimize Weight Loss of Steel Bar in Concrete Exposed to Chloride

The corrosion of reinforced concrete that is exposed to chloride corrosive environment reduces the effective life of concrete structures. The response surface method is based on the central composite design and is used to optimize the relationship among weight loss percentage, additive material percent, concrete cover and water-to-cement ratio. In this research, reinforced concretes made with independent variables, which include additive materials, such as glass, microsilica, and limestone powder, various concrete covers on steel bar and water-to-cement ratios. All samples are exposed to a 3.5 wt% NaCl corrosive environment for 180 days. Experimental methods are used to determine the corrosion of reinforced concrete using the weight loss percentage of steel bar, the chloride penetration rate in reinforced concrete, X-ray diffraction and scanning electron microscope of the steel bar. The result indicates that the least penetration of chloride occurs in reinforced concrete with 10% microsilica powder, 8-cm concrete cover and a water-to-cement ratio 0.45 with superplasticizer. The Minitab software with the response surface method model is used to determine the significance of the independent variables, and their interactions are tested by the variance analysis. The equation among weight loss percentage and independent variables with response surface method model is optimized. The response surface model shows an almost well-optimized performance with R2 (90%) for variables such as weight loss percentage of the steel bar and independent variables.