The objective of this investigation is to experimentally study the behaviour of reinforced concrete (RC) columns strengthened using RC and geopolymer concrete (GPC) jacketing by subjecting them to axial loading. The experimental results were analytically validated by the finite element model (FEM). For this investigation, six columns of M25-grade conventional concrete were subjected to more than 75% of the ultimate load. Then three columns were jacketed by using M40-grade RC and another three columns were jacketed by using M40-grade GPC. The interfacial behaviour of the conventional RC column and jacketed GPC columns was studied and compared. The 3D linear and FEM was employed to measure the effect of conventional RC and GPC-jacketed columns under increasing load by considering the concrete damage plasticity (CDP) and elastoplastic models with isotropic hardening. The validation against the experimental results confirmed 90% accuracy of the analytical model.
Reinforced concrete structures undergo deterioration in a variety of ways due to wetting and drying cycles, freezing and thawing cycles, corrosion, chloride attack, tidal zones and other physical/- chemical causes. Therefore, there is a need to improvise the existing structures to meet the precise design requirements. Structural repair and strengthening of the structures have received worldwide attention [1,2]. Depending upon the type of distress, the techniques applied for the repair of damaged structures vary . Some of the methods extensively used for strengthening of reinforced cement concrete (RCC) structures are patch repair, shotcrete, internal or external prestressing, jacketing by concrete and steel and externally bonded fibre-reinforced plastic (FRP) reinforcement .
Maintenance and repair work is estimated to account for about 85 % of the total expenditure in construction worldwide and there is always an increased need for upgrading the existing infrastructure to meet stern design necessities. Therefore, structural repair and strengthening have received considerable attention from researchers . The premature deterioration of reinforced concrete structural members leads to the most critical problems in civil infrastructure. Reinforced concrete elements require repairs or strengthening when service loading causes excessive deflections and cracking. There is a necessity to enhance the service life of the RC element and incorporate the changes of design parameters to satisfy the stringent limits on serviceability and ultimate strength in accordance with the current codes. The replacement of such deficient structural members requires a huge amount of materials produced from natural resources, which is not environmentally feasible. Also, buildings of historical importance need to be preserved. In these cases, it becomes essential to strengthen the existing structural member depending on the type of construction and the condition of damage .
In this research, two sets of low-grade RC columns were strengthened, one set with high-grade concrete jacketing and another set with GPC jacketing. The interface between the concrete and the jacket was analysed with a commonly available FEA package ABAQUS 6.14. The model was projected to forecast the compressive retort of low-grade RC column with high-grade RC and GPC jackets. A 3D nonlinear finite element method was advanced to explain the compressive response of low-grade concrete column by externally confining the high-grade RC jacket. The following inferences are drawn from the analytical studies:
1. The ultimate load-carrying capacity of the confined high-grade RC and GPC jacket in a low-grade RC column improves by 3.0 and 3.5 times than the normal RC column as per the analytical results. In the experimental analysis, ultimate load-carrying capacity of the confined high-grade RC and GPC jacket in a low-grade RC column improves by 3.25 and 3.72 times than the RC column. The comparison of RC column with jacketed column is less important. But compared to the RC-jacketed column, the GPC-jacketed column shows 1.1 times more loadcarrying capacity.
2. Using the embedded element technique in which the coefficient of friction was fixed at 1.55, an average displacement of 0.6 mm in column’s outer surface and 0.66 mm in inner jacket’s surface is obtained.
3. From the initial to the final stage of loading, the maximum interface shear stress is 2.1 MPa and the maximum interface slip is 0.6 mm for the column’s outer surface and 0.68 mm for RC jacket’s inner surface.
4. The stick/slip concept describes a surface in the contact pressure versus shear stress space in which there is a point of shift from sticking to slipping. The portion below the line in the pressure versus shear stress graph depicts the slip/stick region.
5. In the experimental investigation, the GPC jacket shows 12.5 % less deflection, 14.28 % more reaction force and 28.6 % more stiffness than the conventional RC jacket. In the analytical investigation, the GPC jacket shows 15.2 % less deflection, 14.11 % more reaction force and 28.6 % more stiffness than the conventional RC jacket.
The validation against the experimental test results confirmed 90 % accuracy of the analytical model. The advantage of strengthening the columns using GPC and RC jackets will increase the uniform distribution of strength and stiffness of the column.