Effect of elevated temperature on bond between steel reinforcement and fiber reinforced concrete

• Published in: Fire safety journal Vol. 43; no. 5; pp. 334 - 343
• Main Authors: Haddad, R.H., Al-Saleh, R.J., Al-Akhras, N.M.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.07.2008; Elsevier Science
• Subjects: Applied sciences; Bond; Building structure; Building technical equipments; Buildings; Buildings. Public works; Concrete; Construction (buildings and works); Exact sciences and technology; Fibers; Fire; Fire behavior of materials and structures; Fire protection; Pullout; Reinforced concrete structure; Concrete; Bond; Fire; Pullout; Fibers; Mechanical properties; High temperature; Experimental study; Pull out test; Adhesive strength; Failure analysis; Fires; Fiber reinforced concrete; Concrete construction; Reinforcing bar
• ISSN: 0379-7112
• DOI: 10.1016/j.firesaf.2007.11.002

The bond behavior between fiber reinforced concrete and 20-mm reinforcing steel rebars was evaluated under elevated temperatures. Fifty modified pullout specimens (100×100×400 mm) were prepared using high strength concrete with basalt aggregate and different volumetric mixtures of three types of fibers, namely brass-coated steel fibers, hooked steel fibers, and high modulus polypropylene fibers, before being cured for 28 days at 40 °C. Specimens, designated for heat-treatment, were then subjected to elevated temperatures, ranging from 350 to 700 °C, whereas unheated (control) ones were left in laboratory air. The overall response of control and heat-damaged specimens, pulled out up to failure, and cracking extent and continuity were described. Standard cubes (100 mm 3) were cast, cured, and heat treated under similar conditions, then tested to evaluate compressive and splitting strengths. The results showed marked reductions in residual compressive, splitting and steel–concrete bond under high temperatures with dramatic changes in bond stress–free-end slip trend behavior. Use of fibers minimized the damage in steel–concrete bond under elevated temperatures and hence the reduction in bond strength. Specimens which incorporated hooked steel fibers attained the highest bond resistance against elevated temperatures followed, in sequence, by those prepared with the mixture of hooked and brass-coated steel, the mixture of hooked steel and polypropylene, and brass-coated steel fibers. Statistical models for bond stress versus free-end slip and bond strength versus exposure temperature were developed. These showed excellent agreement with the trend behavior of present experimental data.