Durability is the most important property of Hardened Concrete after Strength. Durability effects by:-
- Reaction with Aggregates
- Attack by Sulfates
- Reaction with Organic Chemicals
- Corrosion of Steel
I. Weathering effect on Durability
Freeze-thaw. Length changes due to temperature change. Wetting and drying.
II. Alkali-Aggregate Reaction(AAR) effect Durability
- Reaction of silica in aggregate with alkali in concrete cause expansion and thus stresses.
- Generates random cracking pattern.
- Slow 5-20 years.
- Little or no damage with cement with alkali contents of <0.6% (most port lands).
- Use of supplementary cementations mineral admixtures can help combat AAR by reducing amount of cement.
III. Attack by Sulfates effect Durability
- Sulfates (SO4) of Na, K, and Mg present in water can react with concrete resulting in severe deterioration.
- Combated by use of type 20 or 50 cement, or low permeability high density normal Portland concrete.
IV. Efflorescence effect Durability
- White deposits on concrete due to egress of moisture with dissolved calcium hydroxide, and evaporation of water/ precipitation of Ca(OH2).
- May be for water retaining structure or high humidity with in the structure.
- Combated by use of dense concrete.
- In excessive can be some durability problems.
V. Reaction with Organic Chemicals effect Durability
- Concrete exposed to animal waste and organic acids from various industries such as dairies and wood pulp mills is sometimes damaged by surface corrosion.
- The organic wastes may also react with the calcium hydroxide and cause expansion.
- Reduced by good quality concrete with adequate cover of steel.
- Essential to avoid honey comb and to design against structural cracking, low permeability, dense concrete reduces.
- Corrosion potential.
- Enhanced in the presence of chlorides.
VII. Wear effect Durability
- Caused by traffic on floors and pavements and contact with running water in hydraulic structures.
- Wear resistance is increased with increasing strength.
- Low permeability, high density.
- Use of aggregates with high silica contents improves wear resistance.
- Reducing the amount of fine aggregates also reduce wear.
- Good curing is very beneficial to wear resistance.
- Some coatings are available to increase wear resistance.