Bond Performance in Machined Reinforcing Bar for Reinforced Concrete

Abstract

Bond between steel and concrete is surely one of the most important aspects in reinforced concrete (r.c.) structures. The structural behavior in general and the formation of the resistant mechanisms in particular, for r.c. structures depends on bond. Normally bond performance has always been related to the relative rib area; in the recent years, a continuous discussion on code specifications regarding the lowering of the limits for the relative rib area (bond index) is under way. The previous values were based on a wide experimental campaign. In general the latter should guarantee a good level of bond in all the common situations. Moreover building industry increased the use of rebar straightening by means of machines used to straighten and shape rebar in coils for use on construction sites. The straightening produces a damage on the ribs that modifies their geometrical properties, essentially due to the action of the rolling line in which a permanent deformation is induced. In the present work, the experimental results of 60 pull-out tests, carried out according with the RILEM testing method, on ribbed reinforcing bars with different reduced rib profile systematically reproducing the straightening process of coil-reinforcing bar produced are shown. Three different diameters are considered: 8, 12 and 16 mm. The behavior in terms of bond strength response is also compared to the Code provisions and then discussed.