Aggregates

Aggregates

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  
Taranaki Andesites predominent    
Coromandel, Bay of Plenty, Central Volcanic Region Predominatly 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

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TR 11 - Properties of New Zealand Concrete Aggregates