Aggregates
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The common types of aggregate met in practice are :
- Natural sands and gravels
- Crushed rocks (igneous, sedimentary, metamorphic)
- Manufactured aggregates (iron blastfurnace slag, expanded clay and shales, sintered pulverised fuel ash, polystyrene beads)
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The availability of aggregates for concrete in New Zealand is summarised in the table below:
| Area |
Igneous |
Sedimentary |
Metamorphic |
| Northland |
Basalt throughout but poorest in the west |
Greywacke-argillite in the east |
|
| Auckland, Waikato, King Country |
Basalt in Auckland, andesite |
Widespread greywacke-argillite quarries. Chert used for decorative purposes |
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| Taranaki |
Andesites predominent |
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| Coromandel, Bay of Plenty, Central Volcanic Region |
Predominatly volcanic with andesites common Greywacke-argillite in east but often of poor quality |
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| East Coast |
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Greywacke-argillite both quarried and as gravel. Limestone used in Gisbourne area |
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| Wellington |
|
Greywacke-argillite both quarried and as river gravel |
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| Marlborough, Canterbury |
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Principally greywacke-argillite gravels |
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| Nelson, Westland |
Granite |
Greywacke and limestone |
Quartzite |
| Otago, Southland |
Basalt and phonolite |
Greywacke and schist gravels |
Schist |
Table 1: Availability of aggregates for concrete in New Zealand
Download
TR 11 - Properties of New Zealand Concrete Aggregates.