Title: Tensile Crack Exposure Tests of Stressed Reinforced Concrete Beams

Author(s): Thomas B. Kennedy

Publication: Journal Proceedings

Volume: 52

Issue: 6

Appears on pages(s): 1049-1063

Keywords: no keywords

DOI: 10.14359/11660

Date: 6/1/1956

Abstract:
Eighty-two reinforced beams were made of concrete with a nominal compressive strength of 3500 psi at 28 days. Air-entrained and non-air- entrained concrete were used. Seventy-four beams were reinforced with rail-steel bars, of which 64 had deformations conforming to ASTM A 306-501’ and IO had old-style deformations. Eight beams were reinforced with billet-steel bars having deformations conforming to ASTM A 305-501’. Coverage over the steel was either s or 2 in. and bars were placed in either bottom or top position when the concrete was placed. Seventy-two beams were stressed from 20,000 to 50,000 psi by third-point loading and in the loaded condition exposed to severe natural weathering at half-tide elevation on the beach at Treat Island, Cobscook Ray, Me. Ten control specimens were exposed but not loaded. Results after three winters exposure indicated that only air-entrained concrete specimens are sufficiently durable to withstand this type of exposure. Evaluation of test results was based on the condition of the specimens after two winters exposure because of the rapid deterioration of the non-air-entrained concrete beams which constituted the majority of the specimens in the program. Specimens with bars having deformations complying with ASTM A 305-50T performed more satisfactorily than did those with old-style deformations. There was no distinguishable difference in the performance of the specimens reinforced with rail-steel or billet-steel bars. Deterioration appeared to increase with increasing stress in the steel, I only for the non-air-entrained concrete. Effect of position of steel, whether at top or bottom at the time of casting, was not apparent in ’ the air-entrained concrete specimens. In the non-air-entrained concrete specimens, those with steel at the bottom at time of casting were more durable than those with steel at the top. No effects of depth of protective concrete over the reinforcing steel were revealed.