X-ray CT Investigation of Bond Mechanism in Reinforced SCC Elements of Different Placement Technology

Abstract

The effect of different placing methods of the self-compacting concrete (SCC) mix—from the top and from the bottom of the form—on the bond failure mechanism was investigated within the scope of this paper. Existing studies regarding the known mechanisms of bond failure do not consider the bottom-up method of concrete placing, which improves the quality of the concrete microstructure around reinforcing bars. Background tests were performed on panel elements with dimensions of 800 × 480 × 160 mm. Ribbed steel reinforcing bars with a diameter of 16 mm were used in the tests, which were placed horizontally in the forms. A pull-out method was used to investigate the bond strength. X-ray computed tomography (CT) was used as a novel and non-destructive technique that allowed a 3D insight into the bond between the rebar and the concrete after the ultimate bond stress had been reached. The results provided a clear description of the phenomena occurring during the fresh state of concrete in the vicinity of rebars (bleeding, plastic settlement, vertical density variation) and showed their significance for bond mechanisms. Finally, it was demonstrated that placing the mix from the bottom of the form resulted in the same bond failure mechanism for both bars located at the top and the bottom of the panel elements. This was translated into identical bond properties throughout the element with regard to bond stiffness and bond strength. It was found that the described and known mechanisms of bond failure are only an idealized description of the performance of the reinforcing bar-concrete joint. The analysis of the steel–concrete interface (SCI) imaging indicated that, in reality, the forming bond failure mechanisms were a complex process that could be affected by many factors.

Application of X-ray Computed Tomography to Verify Bond Failures Mechanism of Fiber-Reinforced Fine-Grain Concrete

“…During the visual evaluation of the tomographic data, attention was given to the concentration of damage around the existing pores. As can be seen in [ 46 ], air pores also exist between the reinforcing bars and the concrete structure, which has little effect on the bonding phenomenon that is the essence of reinforced concrete construction. The distribution, size, and shape of the pores directly affect the safety of the structure.…”

Evaluation of Technical Condition and Durability of Wooden Shaft Guides with Application of Non-Destructive and Semi-Destructive Testing Methods

“…Non-destructive testing methods of constructions in underground engineering most often include visual assessment and surveying techniques [9,10]. More rarely used are techniques based on electromagnetic wave propagation [11] as well as X-and gamma-rays methods [12,13], which are successfully applied in the case of testing typical objects, while in the case of underground structures they rather refer to other materials such as steel or concrete [14,15]. In contrast, semi-destructive methods are characterized by a small influence on an examined object-only small defects occur as a result of the test.…”