Cement and steel The Building blocks of our Economy

Life in cities, and elsewhere, would be inconceivable without cement and steel.

These commodities, with aggregates (gravel), are used in the construction of buildings and infrastructure: e.g., hydro and wind electricity generation and transmission; roads, bridges, overpasses, tunnels; sea and airports; seawalls and flood control schemes; sports and recreation facilities; the oil refinery; and in mining.

The challenge with these bulk commodities is to get them at a good price, and that is a strong incentive for local production, to reduce the transport component of price, which is significant. New Zealand has a cement industry, and a steel mill, at Glenbrook in South Auckland. Our country also imports steel to make up the shortfall in domestic supply. There are around 900 quarries in New Zealand producing aggregates and industrial minerals, such as limestone and clay. Coal is a key ingredient of cement and steel, and is produced in New Zealand.  



Cement and Concrete

Cement is made chiefly of limestone and clay, with coal used as the source of process heat, and to enable the chemical reactions that transform calcium carbonate, alumina-silicate minerals, and iron oxide into a rough product called clinker. When this is finely ground, the result is Portland cement. Discovered by the Romans, the technology was lost after the fall of Rome, to be reinvented in the 1500s.

Cement is then combined with aggregates, including high quality chip and sand to produce concrete. Without concrete we would be without most of the major forms of infrastructure demanded by a modern society, including bridges, hydro and wind generated electricity, overpasses, tunnels, sea and airports, seawalls and flood control schemes, as well as municipal sports and recreation facilities, let alone the foundations pads and walls for commercial or domestic construction.

Steel

Many of these structures require steel, either as re-enforcing or as standalone engineering components. The steel mill at Glenbrook, South Auckland produces in excess of 650,000 tonnes a year for domestic and export consumption and it wouldn't happen without mining and quarrying.

The raw materials include iron sand, coal and lime stone, most of which is mined or quarried in NZ. Electricity, coal and limestone are an integral part of turning the iron sand into iron before it is transformed in to steel. Limestone is also used during the steel making process to draw impurities out of the molten bath. Some additional minerals are added in small quantities to produce different grades.

Our country imports steel products that are uneconomic for New Zealand Steel to make including stainless steel, rails and other specialised products. But steel roofing is a NZ heritage and NZ Steel provides over 80 % of the steel for this end use.

Aggregates

Aggregates – sometimes called “gravel” - covers a wide field of quarried materials including those from traditional “Hard Rock Quarries”, river extraction - usually in conjunction with local body flood control - alluvial and land based sand pits; as well as specialised aggregates, including china clays for pottery and dolomite and limestone for agriculture and the cement industry.

Aggregates are used as “stand alone” products in their own right or combined with other products for end uses such as asphaltic concrete, chip seals and base courses or sub bases for road making; or in concrete for commercial, agricultural or domestic construction. Even the plaster board that lines your walls includes aggregates.

NZ has a well-established quarry industry with around 300 quarries producing aggregates, mostly in close proximity to their end uses; although there are some cities in NZ where demand is starting to exceed local supply, as existing sources are exhausted or there is opposition to expansion of the original site, to take further opportunities with the original resource.