This paper first presented an experimental study on water absorption and tensile properties of basalt fiber-reinforced polymer (BFRP) laminates with different specimen thicknesses (i.e., 1, 2, and 4 mm) subjected to 60 °C deionized water or alkaline solution for an ageing time up to 180 days. The degradation mechanism of BFRP laminates in solution immersion was also explored combined with micro-morphology analysis by scanning electronic microscopy (SEM). The test results indicated that the water absorption and tensile properties of BFRP laminates were dramatically influenced by specimen thickness. When the BFRP laminates with different thicknesses were immersed in the solution for the same ageing time, the water absorption of the specimens decreased firstly before reaching their peak water absorption and then increased in the later stage with the increase of specimen thickness, while the tensile strength retention sustaining increased as specimen thickness increased. The reason is that the thinner the specimen, the more severe the degradation. In this study, a new accelerated ageing method was proposed to predict the long-term water absorption and tensile strength of BFRP laminates. The accelerated factor of the proposed method was determined based on the specimen thickness. The proposed method was verified by test results with a good accuracy, indicating that the method could be used to predict long-term water absorption and tensile strength retention of BFRP laminates by considering specimen thickness in accelerating tests.

Ultrasonic pulse velocity (UPV) has shown effectiveness in determining the depth of surface-open cracks in concrete structures. The type of transducer and the algorithm for extracting the arrival time of the ultrasonic signal significantly impact the accuracy of crack depth detection. To reduce the energy loss in piezoceramic-based sensors, a high-performance piezoceramic-enabled smart aggregate (SA) was employed as the ultrasonic transducer. For the extraction of ultrasonic signal arrival time in concrete, a novel characteristic equation was proposed, utilizing the slope of the signal within a shifting window. This equation was subsequently applied to modify Maeda’s function, with the arrival time of ultrasonic waves defined as the moment corresponding to the minimum Akaike information criterion (AIC) value. Six plain concrete specimens with artificial cracks were prepared and one reinforced concrete beam with a load-induced crack was used for validation. The average deviation of the testing of 492 points on 12 human-made cracks was around 5%. The detection results of 11 measurement points of a crack in a reinforced concrete beam show that three measurement points have a deviation of about 17%. The experimental results demonstrated that the novel piezoelectric transducer and improved AIC algorithm exhibit high accuracy in detecting the depth of concrete cracks.

The bond behavior between a plain bar and concrete has received more attention in recent years because of its importance in the assessment of historical structures. The negative effect of lateral tension on the bond performance of plain bars has been previously investigated through experiments, and the results have shown that the bond strength decreases with increases of lateral tension. However, few attempts have been made to analytically study the bond behavior of plain bars under circumferentially nonuniform lateral tension. Therefore, in this study, a theoretical investigation into the effect of circumferentially nonuniform lateral tension on the bond mechanism and ultimate bond strength of plain bars is undertaken. Based on the theory of elasticity, the compaction of the bar/concrete bond interface is first discussed, and then an analytical model is given for the ultimate bond strength of plain round bars under circumferentially nonuniform lateral tension. The proposed model is verified with experimental results from 96 pull-out specimens, which agree well with the test data. Furthermore, a parametric study is made to show that the proposed model can be applied without concern for separation of the bar/concrete interface for most historical RC structures except those located in humid or marine environments. Finally, the analytical results are compared with a design bond-strength code, which shows that the code could be used in calculating the development length of plain bars under lateral tension.