Repair Materials

1. Cement / Sand Mortars

• Unmodified cement / sand mortars with special waterproofing admixtures added , are the most cost= effective repair materials available for damage areas where the cover exceeds 25mm 

Advantages : 

• Most cost - effective 
• Fire - resistant 
• Less sensitive to changes in temperature . 

Disadvantages : 

• Poor strength in 
• Compression ( squeeze ) 
• FLexure (bend ) 
• High surface permeability 
• Poor adherence to the substrate 
• High shrinkage after setting 
• BOnd failure 

2. Polymer Latex 

• Used in combination with Portland cement to obtain certain advantages such as reduced pemeability , stronger bond to existing concrete , increase in tensile strength of the repair , improve workability & better chemical resistance . 
• Various types of polymer - modified latex : 

1. Polyvinyl acetate ( PVA ) 
2. Styrene butadiene rubber (SBR) 
3. Polyvinylidene Chloride 
4. Acrylics & 
5. Modified acrylic 

Polymer latex acts in several ways : 

• A a water- reducing plasticiser to give better workability & reduce shrinkage . 
• Improves the bond between the repair mortar & the substrate . 
• Reduces the permeability of the repair materials to water , carbon dioxide & oils . 
• Increase resistance of the repair material to chemical attack . 
• Acts to some degree as an essential curing aid . 

Epoxy Resins  

• Most epoxy resin mix used in concrete repairs are solvent free & cure by chemical reaction between the resin & the hardener . 
• Epoxy resin systems develop high strength & have a shorter curing time than cementitious materials , they also have low shrinkage during & after curing . Characteristic 
• Outstanding adhesive qualities  to concrete as well as steel . 
• Resistant to most acids & alkalis & othe chemicals , 
• Rather vulnerable to organic solvents . 
• Low shrinkage when the compound cures & change from liquid to solid state . 
• High compressive , tensile & flexural strength . 
• Poor resistance to fire  

Polyester Resins 

• SLightly cheaper than epoxies but are still considerably more expensive than cementitious mortar . 
• Advantages : 

1. Good resistance to a wide range of chemicals . 
2. high resistance to abrasion & water penetration 
3. High bond strength with most building materials . 
4. The amount of heat evolved during curing is greeater than with epoxies . 
5. Most polyesters do not bond well to damp surfaces . 
6. Little resistance to fire .