The Research On The Interfacial Bond Strength Of New-to-old Concrete

The repair and strengthening of concrete structure has become increasingly important .The adhesion of new-to-old concrete is always encountered in the repair and strengthening of the old building or the newly-built construction.The research on adherence of the new-to-old concrete has become profound significance. It is a simple and effective way to bond new-to-old concrete with interfacial agent. Therefore six interfacial agent are well chosen to bond new-to-old concrete in this paper,which are cement slurry,cement slurry mixed with expanding admixture,silica fume compound-modified cement slurry,styrene butadiene resin(SBR)modified cement slurry,epoxy resin,cement slurry mixed with epoxy ethane.The bonding specimen are tested by such experiments as slant shear ,rupture,direct shear,direct tension and drill and pull-off.Meantime rudimental researches are carried out on the unianxialtensile stress-strain curve of new-to-old concrete.The main results from the tests are as follows:(1) the experimemtal methods to judge the bonding effect of new-to-concrete in this paper are simple,feasibile and can get the same judge result ,among which slant shear is the most effective .Drill and pull-off test is proper to use on the spot. The data got by rupture and direct shear test can provide calculatation parameter for design.(2)Bond strength of new-to-old concrete bonded with cement-based interfacial agent increases with the age and the enhancement of bond strength is very fast in the incipient time ,slow in the late period in general whose bond strength and rule of enhancement is various for different interfacial agent.There are strikingly different bond effectiveness among the different interfacial agent.(3) New-to-old concrete bonded with SBR modified cement slurry has good adhesive effectiveness and long-term bond performance,which nominal bond strength in the age of 14d ,28d ,120d ,180 respectively amount to 106.7%,91.0%,74.1% and 74.9% of the nominal strength of corresponding age of old whole concrete. In this paper SBR modified cement slurry can get best bond effectiveness as interfacial bond materials.(4) New-to-old concrete bonded with silica fume compound-modified cement slurry also has good bond performance which nominal bond strength in the age of 14d and 28d correspond with that of with SBR modified cement slurry ,but lower than the latter in the late period.(5)cement slurry ,cement slurry mixed with expanding admixture and epoxy ethane modified cement slurry can obtain limited bond effectiveness which is not so obvious as the SBR modified cement slurry and silica fume compound-modified cement slurry.(6) New-to-old concrete bonded with epoxy resin has the worst bond performance even can not comparable with the bonding specimen bonded directly with fresh concrete in direct shear ,rupture and direct tensile test.(7) the unianxial direct tensile stress-strain curve of the adhesive specimen can obtain successfully by the method of bonding double steel plate , application of servo machine and using of feedback signal and closed-loop control.The method is effective and feasible and has profound significance for further research on the tensile performance of new-to-old concrete.