Bond of ribbed and threaded steel reinforcement bars post-installed in concrete considering bonded length and...

Post-installing steel bars-or anchors-using chemical agents is nowadays instrumental in repairing and strengthening existing concrete structures. In this experimental research project, beside three cast-in-place specimens provided with ordinary ribbed bars (reference specimens), eighteen specimens were designed and cast to investigate bond performance of chemically-bonded steel bars placed inside concrete blocks, subjected to a pull-out load. Specimens and reinforcement consisted in concrete cubes (side a = 250 mm) and small bars (diameter db = 10 mm). Concrete strength on cubes was 28 MPa. The parameters under investigation were: bonded length (Lb = 5/10/15 db), drilled-hole diameter (= 1.2/1.6/1.8 db), bar properties (ribbed or threaded surface in the post-installed bars) and adhesive type (Sikadur 31CF and Kimapoxy 165). Bond-slip response, bond strength and bar slip at the peak stress, failure modes, as well as bond ductility and stiffness were thoroughly investigated. As expected, in most of the chemically-bonded and cast-in-place specimens bond failure was by steel yielding within a pull out framework (no cover splitting). For the intermediate and largest hole diameters (= 1.6 and 1.8 db), the load-bearing capacity of post-installed bars was slightly larger than that of ordinary bars. In the specimens with post-installed bars, the bearing capacities with Sikadur 31CF and Kimapoxy 165 turned out to be very close for any bonded length. The bond capacity of post-installed threaded bars was from 12 to 21% less than that of post-installed ribbed bars. Compared to ordinary ribbed bars, bond ductility in post-installed bars was higher (from + 18 to + 25% for Lb = 5 db) or even much higher (from 5 to 10 times for Lb = 10 and 15 db). Finally, to evaluate bond resistance of post-installed bars, a new equation is proposed to take care of all major parameters, based on the test results of this study.