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Aggregate

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