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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)

The availability of aggregates for concrete in New Zealand is summarised in Table 1.

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
 
Taranaki
Andesites predominant
   
Coromandel, Bay of Plenty & Central Volcanic Region
Predominantly volcanic with andesites common Greywacke-argillite in east but often of poor quality
   
East Coast


Greywacke-argillite both quarried and as gravel. Limestone used in Gisbourne area

Wellington

  Greywacke-argillite both quarried and as river gravel
 
Marlborough & Canterbury
  Principally greywacke-argillite gravels
 
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