Durability

The New Zealand Building Code states that for a structure, the life of the building must not be less than 50 years unless the specified intended life has been stated. Recognising this fact, the latest version of NZS 3101 contains an entire chapter on durability, which is primarily related to the 50 year life situation.

A suggested approach to cover these requirements is provided in the following flow chart:

Flowchart 1. Designing for durability

Exposure Classification Minimum Required Cover (mm) Specified compressive strength f'c (MPa)
  17.5 20 25 30 40 50 60 70
A1 30 25 25 20 20 20 15 15
A2 50 40 35 30 25 25 20 20
B1 65 50 40 35 30 30 25 25
B2   50 45 40 35 30 30
C   70* 65* 60*
* Also a minimum ordinary Portland cement content of 350 kg/m³ and a maximum water cement ratio of 0.40 is required.

Table 1. Minimum required cover for OPC concrete

General Within 100m of high tide mark, or within 500m of high tide mark to the direction of the prevailing wind or other common wind.
Auckland Region Within 100m of high tide mark, or within 500m of high tide mark to the Southwest.
Wellington Region Within 100m of high tide mark, or within 500m of high tide mark to the North, South or Northwest
Christchurch Region Within 100m of high tide mark, or within 500m of high tide mark to the Northwest, Northeast, or Southwest
Dunedin Region Within 100m of high tide mark, or within 500m of the high tide mark to the Northeast or Southwest

Table 2. Recommendations for defining classification B2 for principal coastal cities 
 

Member & Type of Traffic Min f'c (MPa)
Commercial and industrial not subject to vehicular 25
Pavements or floors subject to:  
a) light pneumatic-tyred traffic (up to 3t gross mass) 25
b) medium or heavy pneumatic tyred traffic (heavier than 3t gross mass) 30
c) non-pneumatic tyred traffic 40
d) steel wheeled traffic To be assessed but not less than 40

 Table 3. OPC Concrete strength for abrasion resistance

Exposure Condition Minimum Characteristics Strength, f'c (MPa) Entrained air for nominal aggregate size (mm)
  10 - 20 40
25 - 49 cycles per annum 20 4 - 8% 3 - 6%
Greater than or equal to 50 cycles per annum 30 4 - 8% 3 - 6

Table 4. Freeze-thaw resistance for OPC concrete

Material Effect
Acetone Liquid loss by penetration. May contain acetic acid as impurity.
Acid 
  • Acetic
  • Carbonic
  • Formic
  • Lactic
  • Phosphoric
  • Tannic
Disintegrates concrete slowly.
Acid
  • Humic
  • Hydrofluroic
  • Nitric
  • Sulphuric
  • Sulphurous
Disintegrates concrete and steel rapidly.
Acid
  • Oxalic
Not harmful. Protects tanks against acetic acid, carbon dioxide and salt water. Poisonous. Should not be used with food or drinking water.
Acid water (pH ≤6.5)¹ Disintegrates concrete slowly. Attacks steel in porous or cracked concrete.
Alcohol (Ethyl, Methyl) Liquid loss by penetration.
Alum (potassium aluminium sulphate) Disintegrates concrete of inadequate sulphate resistance.
Aluminium chloride Disintegrates concrete rapidly. Attacks steel in porous or cracked concrete.
Aluminium sulphate Disintegrates concrete. Attacks steel in porous or cracked concrete.
Ammonia, liquid Harmful only if it contains ammonium salts.
Ammonia, vapours May slowly disintegrate moist concete or attach steel in porous or cracked moist concrete.
Ammonium chloride Disintegrates concrete slowly. Attacks steel in porous or cracked concrete.
Ammonium hydroxide Not harmful.
Ammonium 
  • Nitrate
  • Sulphate
  • Superphosphate
Disintegrates concrete. Attacks steel in porous or cracked concrete.
Automobile and deisel exhaust gases² May disintegrate moist concrete by action of carbonic, nitric or sulphuric acid.
Beef fat Solid fat disintegrates slowly, melted fat more rapidly.
Beer May contain (as fermentation products) acetic, carbonic, lactic or tannic acids.
Calcium chloride Attacks steel in porous or cracked concrete. Steel corrosion may casue concrete to spall.
Calcium sulphate Disintegrates concrete of inadequate sulphate resistance. 
Carbon dioxide³ Gas may cause permanent shrinkage.
Castor oil Disintegrates concrete, especially in presence of air. 
Cinders Harmful if wet, when sulphides and sulphates leach out.
Coke Sulphides leaching from damp coke may oxidise to sulphurous or sulphuric acid.
Copper sulphate Disintegrates concrete of inadequate sulphate resistance.
Creosote Phenol present disintegrates concrete slowly
Ethylene glycol4 Disintegrates concrete slowly.
Fermenting fruits, grains, vegetables or extracts5 Industrial fermentation processes produce lactic acid. Disintegrates slowly. 
Ferric sulphate Disintegrates concrete of inadequate quality. 
Ferrous sulphate Disintegrates concrete of inadequate sulphate resistance. 
Fish liquor6 Disintegrates concrete. 
Fish oil Disintegrates concrete slowly. 
Flue gases Hot gases (200 - 600°C) casue thermal stresses. Cooled, condensed sulphurous andy hydrochloric acids disintegrates slowly. 
Fruit juices Hydrofluoric, other acids, and sugar cause disintegration.
Hydrogen sulphide Not harmful, but in moist, oxidising environments converts to sulphurous acid, distintegrates slowly.
Kerosene Liquid loss by penetration.
Linseed oils Liquid disintegrates slowly. Dried or drying films are harmless.
Lubricating oil, machine oil Disintegrates concrete slowly. Attacks steel in porous or cracked concrete.
Magnesium sulphate Disintegrates concrete of inadequate sulphate resistance. 
Manure Disintegrates concrete slowly. 
Margarine Solid margarine disintegrates concrete slowly, melted margarine more rapidly.
Milk
  • Fresh
  • Sour
 
  • Not harmful
  • Disintegrates concrete slowly.
Mine water, waste Sulphides, sulphates, or acids present disintegrates concrete and attack steel in porous or cracked concrete.
Ores Sulphides leaching from damp ores may oxidize to sulphuric acid or ferrous sulphate.
Paraffin Shallow penetration not harmful, but should not be used on highly-porous surfaces like concrete masonry.7
Petroleum oils Liquid loss by penetration. Fatty oils, if present, disintegrate slowly. 
Pickling brine. Attacks steel in porous or cracked concrete.
Potassium nitrate Disintegrates concrete slowly. 
Seawater Disintegrates concrete of inadequate sulphate resistance. Attacks steel in porous or cracked concrete.
Silage Acetic, lactic acids disintegrates slowly.
Sodium chloride Magnesium chloride, if present, attacks steel in porous or cracked concrete.
Sodium hydroxide
  • 1-10%
  • 20% or over
 
  • Not harmful
  • Disintegrates concrete.
Sodium nitrate Disintegrates concrete slowly.
Sodium sulphate Disintegrates concrete of inadequate sulphate resistance. 
Sugar Disintegrates concrete slowly.
Turpentine Mild attack. Liquid loss by penetration.
Urea Not harmful.
Urine Attacks steel in porous or cracked concrete.

Table 5: Effect of chemicals on concrete

(1) Waters of pH higher than 6.5 may be aggressive if they also contain bicarbonates. (Natural waters are usually of pH higher than 7.0 and seldom lower than 6.0, though pH values as low as 0.4 have been reported. For pH values 3.0, protect as for dilute acid).

(2) Composed of nitrogen, oxygen, carbon dioxide, carbon monoxide, and water vapour. Also contains unburned hydrocarbons, partially burned hydrocarbons, oxides of nitrogen, and oxides of sulphur.

(3) Carbon dioxide dissolves in natural waters to form carbonic acid solutions. When it dissolves to extent of 0.9 to 3 parts per million it is destructive to concrete.

(4) Frequently used as deicer for aeroplanes. Heavy spillage on runway pavements containing too-little entrained air may cause surface scaling.

(5) In addition to the intentional fermentation of many raw materials, much unwanted fermentation occurs in the spoiling of food wastes, also producing lactic acid.

(6) Contains carbonic acid fish oils, hydrogen sulphide, methyl amine, brine and other reactive materials.

(7) Porous concrete which has absorbed considerable molten paraffin and then been immersed in water after the paraffin has solidified has been known to disintegrate from sorptive forces.

(8) However, in limited areas where concrete is made with reactive aggregates, disruptive expansion may be produced.