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:
INSERT FLOWCHART HERE
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
|
80
|
| 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
|
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 sul-phates 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
|
- 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
|
- 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.
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