Repair Of Structures

 

 
Hasan Rizvi
Sr. Vice President
STP Ltd.

Distress In Concrete Structures

The signs of distress in concrete structures include cracking, spalling and disintegration. Cracking, which is one of the most misunderstood problems of concrete, is generally regarded as indicative of defective design or materials. The development of cracking in concrete is due to tensile stress and can be arrested by removing these stresses. Bonding with epoxies, grouting and sealing, stitching, external stressing, grouting, blanketing, use of overlays, etc. are some methods of repairing cracks. Further, the cracks can be closed by inducing a compressive force, enough to overcome the tension and to provide a residual compression.

The process of repairing cracks does not usually involve strengthening. However, 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 the lost strength.

The success of repair and rehabilitation of structures depends on the specific plans designed for it. The protection, repair and rehabilitation procedures for concrete structures depend on the evaluation of concrete’s condition in the structure, relating the condition to the underlying causes of distresses, selecting appropriate repair material and method for any deficiency identified, and using the selected materials and methods to repair or rehabilitate the structure.

Factors Affecting Durability Of Structures

  • Quality construction
  • Lack of waterproofing treatment
  • Poor Maintenance and blocked drainpipes
  • Lack of proper slope, causing stagnation of water
  • Leaking pipe joints

The following points should be considered for both, new construction of concrete and the repair of deteriorated structures.

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. Subsequently, 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.

 

Fig. 1: Usage of ShaliPlast LW++ Shows No Corrosion

The compatibility of material in repair systems and the increased need for performance specifications are all considerations. A major cause for failure of repairs is improper understanding of the structure and causes of the distresses. Once the reasons are identified, a proper repair strategy can be worked out by a qualified Civil Engineer.

 

The penetration of corrosive substances directs corrosion of the steel reinforcement. As the consequent layer of rust has more volume then the original steel bar, it causes tension in the surrounding concrete. The cover of concrete is limited on the outer side, so the resultant tensile force causes formation of cracks; the cracks permit easier entry of water and oxygen to form more rust. This results in increased volume and wider cracks in concrete. The surrounding concrete becomes partly disintegrated, which finally causes spalling.

 

STP Ltd. has been associated with the repair and rehabilitation of numerous structures. Integral Waterproofing-Cum-Corrosion Inhibitor for Reinforced Cement Concrete (RCC) is a revolutionary liquid waterproofing compound that protects concrete internally from water ingress as well as saves the re-bars of reinforced concrete and mortar against chloride induced corrosion. The unique bipolar compound migrates through concrete during curing process and puts a passive layer over rebars to stop chloride corrosion.

 

Repair Of A Township Having Severe Spalling

The structural health of the building was tested, and accordingly, the repair strategy was determined. The repair procedure consisted of:

  • Removing all the damaged/cracked/spalled concrete by tapping with light hammer or 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 and including drilling holes of required diameter for the nozzles at 300 mm spacing along the crack. Further, sealing the nozzle from sides with Epoxy mortar namely ShaliFix EM, and 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 and exterior paint coating ShaliCryl 215 of STP Ltd.

 

   Fig. 2: Before Repair

 

      Fig. 3: After Repair

Conclusion

A proper diagnosis of the problem and using the materials appropriately are among the most important aspects of any repair application.

For more information,
visit: www.stpltd.com