A concrete result

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The word concrete comes from the Latin word “concretus” (meaning compact or condensed),  from “con-” (together) and “crescere” (to grow).

German archaeologist Heinrich Schliemann found concrete floors, made of lime and pebbles, in the royal palace of Tiryns, Greece, which dates roughly to 1400-1200 BC. And lime mortars were used in Greece, Crete and Cyprus as early as 800 BC. 

 

The Roman advance

The Romans used concrete extensively from the period 300 BC to 476 AD. Roman concrete was made from quicklime, pozzolana and an aggregate of pumice. This allowed revolutionary new designs with greater structural complexity and dimension than was possible with brick or stone. While just as strong in compression as modern concrete, the absence of reinforcement meant its tensile strength was far lower.

Roman concrete depended on the strength of the concrete bonding to resist tension. The dome of the Pantheon in Rome (126 AD) is an example of how sophisticated the Romans’ use of concrete was.

Modern structural concrete differs from Roman concrete in two important details. First, the mix is fluid and homogeneous, allowing it to be poured into forms rather than requiring hand-layering concurrently with the placement of aggregate which, in Roman practice, often consisted of stone rubble.

Second, integral reinforcing steel gives modern concrete assemblies much greater strength in tension.

 

Key dates

Key dates in the development of modern cement and concrete were:

1824: The invention of Portland cement in England (named because of its similarity in appearance to the Portland stone found nearby)

1836: The first strength testing of concrete in Germany, and

1913: The first redimix concrete plant set up in Baltimore, Maryland.

Redimix concrete was introduced to the New Zealand market some 75 years ago with the setting up of the first plant in Wellington.

The recent case in Auckland of under strength concrete being delivered to 70 building sites shows how vigilant we need to be to ensure that all products, including concrete, meet expected standards of quality and strength.

 

Building bylaws

The first set of national model building by-laws was published in 1935, following the Napier earthquake.

On February 3, 1931, the Hawkes Bay region was subject to the worst earthquake in New Zealand’s history. The quake measured 7.9 on the Richter scale. The death toll was 256, with fire spreading throughout Napier and Hastings, and major Napier buildings and landmarks completely destroyed.

Areas of coastline were dislodged, and the landscape changed forever. The current Napier airport was once at the bottom of the harbour.

Standards New Zealand was established, to ensure future events did not result in the same loss of life. The first earthquake standard, NZSS 95 was developed in 1935.

There are now more than 650 building-related standards. Many provide guidance for designers and builders on how to comply with the Building Code, benefiting the industry and all New Zealand communities.

 

A modern material

My earliest experience of concrete as a core building material was in England in the late 1960s, where precast concrete was increasingly and once tragically employed, on new council tower blocks.

The tragedy occurred at the Ronan Point Block in East London, when a gas appliance exploded in the corner of a multi-storey block constructed of precast concrete panels.

The panels literally relied on gravity to hold them in place. “House of cards” best describes what occurred after the explosion.

The tragedy led to a serious loss of confidence in tower block living and, particularly, the use of precast concrete construction.

My own parallel experience was working for a company using what was known as “no-fines” concrete. The no-fines mix was poured into forms within reinforced concrete frames and then plastered inside and out.

The concrete mix, quite sophisticated for its time, was deliberately low in fine aggregate, creating a wall panel that was low in weight and high in insulation quality.

In recent years we have seen a return, in a different way, to the so-called brutalism period of the 1960s, using exposed concrete as structure and final decoration.

The term brutalism does not come from “brutal”, but from the French “beton brut”, or “raw concrete”. The term was invented by French/Swiss architect Le Corbusier, who was best known for designing the Punjab capital city of Chandigarh in northern India.

There, the availability of very cheap labour, coupled with the need for a material requiring little or no maintenance, led to the use of concrete for structure and finish.

The use of concrete as a structural and cladding material continues to develop, assisted by increasing levels of innovation applied to its make-up and form. Today, very thin precast wall panels, many with an insitu finish, are seen on virtually every major building site.

The combination of speed and convenience of off-site manufacture and instant enclosure is revolutionising medium-scale construction.

In the future we are likely to see such innovations as self-healing concrete which reacts to the ingress of moisture, and self-cleaning mixes which reduce surface pollution. The Auckland Sky Tower is an example of a specially designed, very dense concrete mix that still looks as clean as the day it was poured.

The use of polished concrete floor finishes, often with coloured tints applied to the mix, has added a robust and an environmentally-friendly approach to domestic construction.

Environmentally friendly? No need for floor coverings with high and often chemical-based manufacturing processes, plus the use of the concrete slab as a heat sink, absorbing the sun’s heat during the day, thus reducing evening heating costs.