A Comparison of the Bond Strength of Spun and Static Cast Concrete Specimens

The purpose of this study is to determine the pullout bond strength of seven wire steel strand in two types of concrete: spun and static cast. It is perceived that the spinning process used in the manufacturing of concrete poles introduces compaction forces that densifies the concrete and hence, improves the steel to concrete bond. Studies have successfully been conducted determining the bond strength of steel and concrete using the pullout test method; however, there are not any studies known of that address centrifugally cast concrete.;In order to obtain data for the research, an experimental program was designed to perform pullout tests on 112 test samples. Two sets of tests were conducted. Series 1 contained 14 inch long static and spun concrete specimens with embedded seven wire 270 ksi grade steel strand, whereas series 2 contained 12 inch long static and spun concrete specimens with embedded seven wire 270 ksi grade steel strand. Spun specimens were made in steel molds and spun according to the process used in the manufacturing of spun concrete poles. A pullout test setup was designed using a Universal Testing Machine; load was applied at a rate of 3,000 pounds per minute until ultimate failure (slip) occurred. During the procedure, slip of the steel strand was recorded for each load increment. Data collected was used to determine the pullout load at ultimate failure and the average bond strength. The results were evaluated to compare the bond strength of centrifugally and conventionally cast concrete.