Factors affecting the bond strength between new and old concrete

Abstract

One of the main concerns in repair is a sufficient bond between the substrate and the repaired material, especially for the long-term performance and durability of the structure. We carried out in this study an experimental work to investigate the effect of main parameters that primarily influence the bond between old and new concrete in dry, hot weather. The compressive strength considered for the case of old concrete is 15 MPa. While for the case of the new concrete, the considering compressive strengths as 15, 30, 40, and 50 MPa. We cast a total of 48 cube samples (10×10×10 cm) and tested them for the grade of old concrete, the new concrete as a jacket in both faces of the old one. We prepared the substrate surface by grinding. We cast the new concrete over the old concrete where four cases of the bond between old and new concrete considered included 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 50 0 C 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 a bond agent or dowels remarkably influenced the bond between old and new concrete and gave the same results, but using both gave maximum shear strength than other considered cases.