Strengthening of Corroded Reinforced Concrete Columns using Ultra –high Performance Concrete

Abstract

In this research, the connection technique between UHPFC jacket and corroded concrete column was done by roughening the surface (sand blasting) and after that applying a binder (epoxy LB32).Using normal strength concrete (NSC) with similar longitudinal and transvers reinforcement, fourteen square and circular column samples with a cross-section (150*150) mm and an overall length of 950 mm were casted. The thicknesses of the jacket were (20mm and 40mm) and the shapes of the columns. They were tested, in compression under different levels of corrosion (10%, 20% mass loss) while one of them was used as a reference without any strengthening. The outcomes of the research show that the increase in the thickness, from 20 to 40 mm, of UHPFRC jacket leads to an increase in the carrying load by about ( 49%,117%) at 10 % mass loss and ( 84%, 119%) for 20 % mass loss for square retrofitted concrete columns, while for circular ones, the load carrying capacity change by about ( 97%, 125%) for10% mass loss and ( 28% , 83%) for 20% as compared to the reference column. The crack take more time to appear and was more uniformly distributed for both cases. Deformation of specimens has an impact on the results as follow: with the mid-height lateral deformation of columns change by (131%, 108%) for square columns with mass loss 10% and (121%, 64%) with mass loss 20%. In contrast, for circular columns, the decrease was about (51%,45%) for 10% mass loss and (83%,52%) for 20%. Furthermore, the axial deformation of concrete specimens decreased about (91%.89%) and (66%, 95%) for 10% and 20% mass losses respectively for square columns. However, regarding to circular columns, these changes were (99%, 96%) and (98%, 96%) for the same cases. The ductility of corroded concrete columns that strengthened with UHPFRC jacket significantly enhanced by (6%, 47%) for 10% mass loss and (82%, 83%) for 20% mass loss for square columns. And (63%, 68%) and (21%, 49%) for circular columns with mass loss 10% and 20 % respectively. It can be concluded that when the thickness of the UHPFRC jacket has been increasing, the initial and secant stiffness have improved as a result of increased column size and improved modulus of elasticity. The change of initial stiffness’s were about (73%,254% ) and ( 407%,673%) for square concrete columns with mass loss 10% and 20% , while II they were improved by (223%, 192%) ,(17%,184%) for circular columns with same mass losses. However, the total stiffness improvements were ( 63%,144%) and (178%, 321%) for square columns with mass loss of 10% and 20% respectively. Regarding to circular columns, these improvement for the total stiffness were (99%, 135%) and (-4%, 91%) with respect to the damage un-strengthened concrete columns. Because the increase in the size of the specimens, the cracks were delayed and the performance was better than the reference column.