Materials for Repair of Concrete Structures – Types and Selection Criteria

There are various types of materials which are used for the repair of concrete structures. For instance, unmodified Portland cement mortar or grout, latex modified Portland cement mortar or concrete, quick setting non-shrink mortar, and polymer concrete. The choice of such materials is based on their performance and cost. In addition to repair material compatibility with damaged structure and ease of application.

When deterioration is due to chemical attack, it may be necessary to use a different cement or protective coatings. The repaired concrete fails mainly due to the failure or partial failure of the bond between the old and new work. The standard of bond developed between the old and new concrete is directly related to the care taken in the preparation of the base concrete. Therefore, not only does a successful repair work requires excellent selection of repair materials but also it needs practising proper execution procedure.

Selection Criteria for Repair Materials

• Ease of application
• Cost
• Available labor skills and equipment
• Shelf life of the material
• Pot life of the material
• Type of damage
• Compatibility of the repair material with damaged concrete
• Appearance of finished surface
• Co-efficient of thermal expansion of the material
• Co-efficient of permeability of the material
• Corrosion resistance property of the material
• Durability of such concrete repair material
• Speed of concrete repair

Common Repair Materials

Following are the some of the common repair materials used for repair or rehabilitation or strengthening of the concrete structures:

1. Unmodified Portland Cement Mortar or Grout

Portland cement mortar or grout is the most common repair materials used for repairing damages to concrete structures. It is selected because it is readily available and has a low cost.

This material consists of ordinary Portland cement and suitable aggregate. Cement mortar is generally used for small repair works and cement concrete are commonly selected where a large area is to be repaired.

Fig. 1: Unmodified Portland Cement Mortar

2. Latex Modified Portland Cement Mortar or Concrete

This repair material is used to prevent chloride attack on concrete structure due to the use of low water-cement ratio. This is the same as ordinary Portland cement mortar or grout with the addition of a latex emulsion. The strength of this material is same as ordinary mortar or grout. Ingress can be reduced due to lower water-cement ratio.

The addition of latex modifier influences the strength and durability of cement. The use of this material should be based on the service conditions of the structure.

Latex modifier concrete recommended for sections up to 30mm deep, should have 1:3-3.5 as the ratio of cement and fine aggregates. Water ratio should be 0.3 with latex solid cement ratio of 0.1 to 0.2 by weight. Latex modifier concrete recommended for sections deeper than 30mm should have proportions of 1 part of cement to 2.5-3 parts fine aggregate to 1.5-2 parts coarse aggregate.

Fig. 2: Latex Modified Mortar

3. Quick Setting Non-shrink Mortar

Cracks on concrete surface due to shrinkage of concrete are repaired by this material. It develops a good bond with old concrete. The use of suitable admixtures combined with this repair material also increases strength and improve bond and workability while reducing curing time.

Polymer Concrete Most popular polymer concrete used is an epoxy concrete system with curing agents or methyl methacrylate monomer with an inhibitor and promoter. Epoxy system is widely available in formulated repairing materials. This repair material can be customized as per the requirement for use in repair of different types of concrete damages.

Fig. 3: Quick-set Non-shrinking Mortar