Experimental study on the acoustic wave velocity in steel-reinforced mortar under external pull-out load

One of the major safety issues concerning the bond stress of mortar and con crete elements under external loads has been investigated. The relationship between bond stress and acoustic wave velocity has been analyzed for diffe rent cement/sand ratios. This study pioneers the combination of pull-out te sts on standard concrete specimens with acoustic through-transmission measu rements, and lays the groundwork for future on-site inspection of steel-rei nforced structures. Changes in acoustic wave velocity were observed as the bond stress exceeded a certain level. As the external pull-out load (transf erred to induced bond stress) increases, the acoustic wave velocity decreas es. This phenomenon becomes very significant as the pull-out load approache s the maximum bond strength of the specimen. For a one-to-one cement/sand r atio, a mere 5% decrease in velocity ratio is critical to structural safety , since a 1.4 safety-factor can assure the bond condition only up to 71% of the maximum load, compared to 70% of the maximum load in more than 60% of the measurements. (C) 1999 Elsevier Science B.V. ALI rights reserved.