Required Properties of Concrete Repair Materials

The essential parameters for deciding upon a repair material for concrete are:

1) Low shrinkage properties

2) Requisite setting/hardening properties

3) Work ability

4) Good bond strength with existing substrate

5) Compatible coefficient of thermal expansion

6) Compatible mechanical properties to that of the substrate

7) Should allow relative movement, if expected particularly in case of sealing of cracks or dealing with expansion joints.

8) Minimal or no curing requirement

9) Alkaline character

10) Low air and water permeability

11) Aesthetics to match with surroundings

12) Cost

13) Durable, non degradable or non-biodegradable due to various forms of energy life, UV rays, heat etc

14) Non-hazardous/non-polluting

Low Shrinkage of Concrete Repair Materials

Cementitious repair materials shrink with passage of time. Most of the shrinkage generally takes place in the initial period from the time of casting to 21 days. Therefore, repair material in its original form, if used for repair of concrete/mortar, is likely to get either delaminated due to debonding or develop shrinkage cracks on its surface due to shrinkage strains and stresses.

Requisite setting/hardening Properties

It is desirable that the repaired structure shall be put to use at the earliest possible to reduce the downtime of plant, machinery, building or road. It is therefore, essential that repaired patch shall harden in the minimum possible time.

However, in exceptional cases, it could also be essential to have the slow setting property as a desirable property for repair material. Such situation could be where more working time is required to work on repair materials or the repair process is intricate that more working time is required.

Workability of Concrete Repair Materials

The repair material is to be applied by the field workers and hence its acceptability by them is very important. The property desired by the field workers is good work ability. Hence optimum work ability is to be achieved without sacrificing the other desirable properties by use of suitable additives/admixtures.

Bond with the Substrate

The bond strength of repair patch with the substrate is essential to have a successful repair system. If it is felt that the bond strength of the repair material with the base material is inadequate or less than the strength of the base material, then some other suitable means could be explored to improve the bond strength between the repair material and substrate.

These could be use of:

Adhesives Surface interlocking system Mechanical bonding A variety of adhesives, in the range of epoxies, polymer modified cement, slurries including unmodified polymer applications are available. The selection depends upon available open time for bonding etc, which are being specified for different applications.

Compatible Coefficient of Thermal Expansion

The difference in volume change because of temperature variations can cause failure either at the bond line or within the section of lower strength material.

The primary ingredients for most repair materials include one or more of the following:

(i) Ordinary or rapid hardening Portland cement

(ii) Epoxy resins

(iii) Polymer latex

(iv) Polyester resins

(v) Polyvinyl acetate

(vi) Fine and /or coarse aggregate filler