Experimental Investigation On Determination Of Bond Strength For Various Types Of Concrete Used at Sites

Abstract

The shear stress developed at the interface of concrete and bar is called bond stress. And, with the advancement and development in technologies for the preparation of Concrete and Steel it has become important to investigate the bond strengths of these engineered materials as bond stress mentioned in IS: 456 – 2000 are the same since 1964. But with enormous improvement in the field of concrete and steel these values of bond strength are bound to differ and hence the study of bond strength is essential. The study of bond strength is important as the flow of forces from concrete to steel and vice-versa takes places depending upon bond values. Procedures mentioned in IS: 2270 (Part 1)–1967, “Methods of Testing Bond in Reinforced Concrete”, is used to carryout the pull-out test. The study consists of casting five different grades of concrete i.e. M 20, M 25, M 30, M 35 and M 40 with three different types of concrete mix which were mix with Fibres and Super-plasticizer, mix with Super-plasticizer and Normal mix. With this, three different diameter of reinforcement bar 12 mm, 16 mm and 20 mm and three different type of reinforcement bars namely Mild steel, TMT and TMT Coated were used. Specimens for measuring mechanical properties like compressive, flexural and tensile strength of all these different mix were also cast. In total there were 585 specimens tested. Out of these, 405 specimens were pull-out specimens and the rest 180 specimens were for finding the mechanical property of concrete. Pull-out test was carried out on 28 days with the loading rate as mentioned in the IS: 2770. From the results so obtained, bond strength and Load-Slip curves for all the specimens were plotted and discussed. Also analytical study was carried out using “SAP 2000” and the results obtained are compared with the experimental results. From the experimental study, it was found that: 1. Mix with Fibres and Super-plasticizer were able to provide greater bond strength 2. TMT bars were able to provide greater bond strength than the other two materials 3. With the increase in diameter of the bar the bond strength decreases for the same size of specimen. 4. The values of bond strength were on much higher side than the IS: 456-2000 bond stress values. 5. Also it was found that the required development length was largely reduced by considering the values of bond strength obtained from the experimental work. From the analytical study, it was also found that that with the increase in the diameter of bar the bond strength decreases. This study encouraged the need for revising the bond strength values mentioned in IS: 456-2000.