الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
One of the main concerns regarding repair is that there is an adequate bond between the substrate and the material being repaired, especially for the long-term performance and durability of the structure.
In the present study, we carried out an experimental work to investigate the effect of the main parameters that primarily influence the bond between old and new concrete in both shear and bending in dry and hot weather compared to samples curried in water. The compressive strengths considered in the case of old concrete for cubes cast to investigate the shear strength at the interface are 15, 20 and 25 MPa. While in the case of the new concrete, the considered compressive strengths were 15, 25, 30, 35, 40, and 50 MPa, the compressive strengths of the old concrete in the case of investigating the bond at the interface under bending were 20 and 25 MPa, the new overlay strengths in this case were 25 and 30 MPa.
A total of 132 cube samples (10×10×10 cm) were casted and tested them for the grade of old concrete, the new concrete as a jacket in both faces of the old one, moreover 12 concrete slabs with thickness 10 cm representing the old concrete and new topping with 5 cm thickness represented the new concrete were also prepared and tested.
We prepared the substrate surface for the cubes by grinding. We casted the new concrete over the old concrete where four cases of the bond between old and new concrete were considered included using bond agent, dowels, bond agent and dowels, and without any bond agents or dowels. The samples were saved in the oven at 500C for 28 days and other samples in the water until the test day. In contrast, the old concrete slabs surface was left as cast and the new topping was casted after 28 days from casting the old concrete, and the samples were tested after 4 weeks from casting the new concrete.
Test results of the cubes indicated that using new concrete with higher compressive strength within the studied range slightly affected the bond between old and new concrete while using the bond agent or dowels substantially influenced the bond between old and new concrete and both gave almost same results. However, using both gave maximum shear strength than other considered cases. Regarding the slabs, using an adhesive agent gives the best result of the bond strength at the interface.
Bending test results for the slab showed that using shear connectors give the best ultimate load for all cases with compared to other substrate surface preparation. Substrate surface without using any bonding agent gives the lowest ultimate load. Slabs with an adhesive agent give the minimum deflection for all specimens and shear connectors increase the ductility of the slabs more than other substrate surface cases.