Corrosion pits on pipelines lead to the formation of small holes, which cause further pipeline damage and even catastrophic consequences. Since many pipelines are located underground, the detection of corrosion pits on pipelines in real time is still an engineering challenge. In this paper, an experimental feasibility study on pipeline corrosion pit detection using the time reversal technique with a piezoceramic transducer as a time reversal mirror was investigated. A specimen of steel pipeline section was fabricated with an artificially drilled hole, which was to mimic a corrosion pit. By gradually increasing the depth of the hole, the evolution of the corrosion pit on the pipeline was simulated and studied. Two piezoceramic transducers were employed to generate a stress wave to propagate along the pipeline and to detect the propagated stress wave. With both the properties of sensing and actuating functions, a piezoceramic transducer was used as a time reversal mirror, which first detected the propagated stress wave signal and then sent ‘back’ the time-reversed signal as a propagating stress wave. With the inherent auto-focusing property of the time reversal technique, the detected time-reversed stress wave had a distinct focused peak. A corrosion pit on a pipeline, as a structural defect, reduces the energy of the focused signal received by the piezoceramic sensor and the attenuation ratio of the focused signal depends strongly on the degree of corrosion depth. Experimental results show that the amplitudes of the focused signal peak decrease with the increase of corrosion pit depth and we can use the peak amplitude of the focused signal to determine the state of pipeline corrosion. The time reversal based method proposed in this paper shows the potential to quantitatively monitor the damage degree of corrosion pits on pipelines in real time.

This paper presents an experimental investigation of flexural behavior of circular ultra-high-performance concrete with coarse aggregate (CA-UHPC)-filled steel tubes (CA-UHPCFSTs). A total of seven flexural members were tested under a four-point bending load. The failure modes, overall deflection curves, moment-versus-curvature relationships, moment-versus-strain curves, strain distribution curves, ductility, flexural stiffness and ultimate flexural capacity were evaluated. The results indicate that the CA-UHPCFSTs under bending behaved in a good ductile manner. The CA-UHPC strength has a limited effect on the ultimate flexural capacity, while the addition of steel fiber can improve the ultimate flexural capacity. Increasing the steel tube thickness leads to higher flexural stiffness and ultimate flexural capacity. There is a significant confinement effect between the steel tube and the CA-UHPC core in the compressive zone and centroidal plane after the specimen enters the elastic-plastic stage, while the confinement effect in the tensile zone is minimal. Moreover, the measured flexural stiffness and ultimate flexural capacity were compared with the predictions using various design specifications. Two empirical formulas for calculating the initial and serviceability-level flexural stiffness of CA-UHPCFSTs are developed. Further research is required to propose the accurate design formula for the ultimate flexural capacity of CA-UHPCFSTs.

This paper investigated the influence of recycled ceramics and grazed hollow beads on the mechanical, thermal conductivity and material properties of concrete. The results showed that the concentration of recycled ceramics and grazed hollow beads has significant optimization on the workability and thermal properties of the concrete. However, the superabundant concentration can reduce the hydration degree of the concrete, which results in the suppressed production of C-S-H gel and the increase of material defects. In summary, considering the coordinated development of key factors such as thermal insulation properties, mechanical properties and microstructure, 10% RCE and 60% GHB are the optimal material system design methods.