Bond strength of reinforcing steel bars in high strength concrete

In last years, a great attention has been given to use silica fume as apozzolanic material to produce a high strength concrete. This very fine materialwas found to improve various physical and mechanical properties of concrete.In this work, the behavior of concrete compressive strength and steel-concretebond are experimentally investigated due to addition of different silica fumepercents. The silica fume contents are 0, 5, 10 and 15 % by weight of cementcontent. Three levels of cement content, 450, 500 and 550 kg/rrr’ are used.Gravel and basalt are used as coarse aggregate to show the effect of coarseaggregate types on the steel - concrete bond in high strength concrete, (HSC).Plain and deformed bars, are used to investigate the contribution of steel- HSCbond mechanisms. Two different types of pull out test techniques (UK test andcontrolled embedded length test) using British Standard concrete cylinder witha centered steel bar to evaluate the bond strength are used.The results of the present work show an obvious effect of the silica fumeaddition and coarse aggregate type on the behavior of compressive strength andsteel - concrete bond in HSC. The rate of increasing in bond stress with theaddition of silica fume is different from that of the compressive strength.Moreover, the compressive strength is not the only main factor controlling thesteel - HSC bond. The factor of silica fume content is of prime importance inthe analysis of bond strength in HSC. The bond stress is not directlyproportional to the cement content as found in the behavior of the compressivestrength. On the other hand, the bond stress in basalt concrete is higher thanthat of gravel concrete at all levels of compressive strength.