Factors affecting the bond strength between new and old concrete

Document Type : Original Article

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Civil engineering department, faculty of engineering, Minia, Egypt

Abstract

One of the major concerns in repairing is a sufficient bond between the substrate and the repaired material, especially for the long-term performance and durability of the repaired structure. In this study, experimental work has been carried out to investigate the effect of key parameters that primarily influence bond between old and new concrete in a dry hot weather. The compressive strength was considered for case of old concrete which is 15 MPa, while for case of new concrete the considered compressive strengths were 15, 30, 40 and 50 MPa. A total of 48 cube samples were casted and tested, where 48 cube samples (10×10×10 cm) were casted for the grade of old concrete, after which the new concrete were casted as a jacket in both faces of the old concrete. The substrate surface was prepared by grinding. The new concrete was casted over the old concrete where four cases of bond between old and new concrete were considered including using bond agent, using dowels, using bond agent and dowels, and without using bond agents or dowels. The samples were saved in the oven at 500C for 28 days till the test day. Test results indicated that using new concrete with higher compressive strength slightly affected the bond between old and new concrete, while using bond agent or dowels remarkably influenced the bond between old and new concrete and gives the same results but using both of them give maximum shear strength than other considered cases.

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