Cement, Concrete & Steel The Building blocks of our Economy

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

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 New Zealanders take for granted, including bridges, hydro and wind generated electricity, overpasses, tunnels, sea and airports, seawalls and flood control schemes sports and recreation facilities.

Steel

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

The raw materials include iron sand, coal and limestone, most of which are mined or quarried here in New Zealand. 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 to draw impurities out of the molten bath. Additional minerals are added in small quantities to produce different grades of steel.

We import steel products that are uneconomic for New Zealand Steel to make, including stainless steel, rails and other specialised products. But steel roofing is a New Zealand heritage and NZ Steel provides over 80 percent of the steel used for this purpose.

Aggregates

Aggregates – sometimes called “gravel” - cover 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 standalone products or combined with other materials for end uses such as asphalt, 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.

New Zealand has a well-established quarry industry with around 900 quarries producing aggregates, mostly close to where they are used. However, in some cities demand now exceeds local supply as existing sources are exhausted or there is opposition to expansion of the original site. This means aggregates must be transported greater distances, adding to their costs and to emissions.