Repairing Cracks In Concrete Structures

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Major signs of distress in concrete structure: are cracking, spalling and disintegration. Cracking is one of the most misunderstood problems of concrete. It is generally regarded as indicative of defective design or materials. Methods of repairing cracks include bonding with epoxies, routing and sealing, stitching, external stressing, grouting, blanketing, use of overlays, etc. Repairing cracks does not usually involve strengthening. In a structure showing spalling and disintegration, it is usual to find that there have been substantial losses of section and/or pronounced corrosion of reinforcement. Hence, the repair involves some requirement for restoration of lost strength.
Development of cracking in concrete is due to tensile stress and can be arrested by removing these stresses. Further, the cracks can be closed by inducing a compressive force, enough to overcome the tension and to provide a residual
feature-top Spoksperson:
Hasan Rizvi
Sr. Vice President
STP Ltd
www.stpltd.com
compression. The success of repair and rehabilitation of Structures depends on the specific plans designed for it. Concrete Structures: Protection, Repair and Rehabilitation procedures depend on evaluating the condition of concrete in the structure, relating the condition of the concrete to the underlying causes of distresses and selecting appropriate repair material and method for any deficiency found, and using the selected materials and methods to repair or rehabilitate the structure. STP Ltd has been associated with Repair & Rehabilitation of numerous structures.
The following points should be considered for both, new construction of new concrete and the repair of deteriorated structures.
Factors Affecting the Durability of Structures
- Quality construction
- Lack of waterproofing treatment
- Poor Maintenance, blocked drain pipes
- Lack of proper slope causing stagnation of water
- Leaking Pipe joints
The compatibility of materials in repair systems and the increased need for performance specifications are very important. A holistic model for deterioration considers the effect of both the scientific facts and the experimental knowledge of environmental factors and how they affect each component of the structure. To achieve durable repairs, it is necessary to consider the factors affecting the design and selection of repair systems as parts of a whole or as components of a composite system
The reasons for Repairs to fail are due to improper understanding of the structure & causes of the distresses. Once the reasons are identified, a proper Repair strategy can be worked out by a qualified Civil Engineer.
The corrosive substance penetration helps corrosion of the steel reinforcement. As the rust has more volume then the original steel bar, the rust causes tension in the surrounding concrete. As the cover of concrete is limited on the outer side, the resultant tensile force causes crack formation and the cracks permit easier entry of water and oxygen to form more rusting - resulting in an increase in volume and the cracks in concrete get wider and wider. The surrounding concrete becomes partly disintegrated, which finally causes spalling.
Repair of a township having severe spalling: Structural health of building was carried out and accordingly the repair strategy was determined. The Repair procedure consisted of removing all the damaged / cracked / spalled concrete by tapping with light hammer/ chipping with chisel/High pressure water jet/Compressed air etc. Cleaning and removing all loose and defective concrete/ materials, cleaning of all corroded/rusted reinforcement bars up to 28 mm diameter using Rust Remover ShaliRust Off of STP Ltd, mixing extra reinforcement as required by welding , applying Epoxy Resin based Primer ShaliPrime ZnR , Applying a single coat of Epoxy Resin based bonding agent ShaliBond Concrete of STP Ltd, Fixing standard injection nozzles of 10/12 mm diameter after and including drilling holes of required diameter for the nozzles at 300mm spacing along the crack, sealing the nozzle from sides with Epoxy mortar namely Shalifix EM , Injecting through the fixed nozzle Epoxy injection Resin Grout: ShaliGrout EI , applying pre packed cementitious patch repair mortar ShaliFix RM of STP Ltd , applying surface protection, exterior paint coating ShaliCryl 215 of STP Ltd.
Proper application of material is among the most important aspect of any Repair application. STP Ltd has started a training institute called STP Institute of Waterproofing & Protective Coating. The aim is to develop applicators, so they can diagnose the problem and repair using the materials in the right way.