45 Fun Facts About Concrete

Concrete is the second-most-used substance in the world after what?

Water: concrete is the most widely used substance after water, and making its cement accounts for up to 8% of global CO2 emissions.

What are the two basic components of concrete?

Aggregate bound by a cement: the aggregate must be clean, because dirt or clay clinging to it can weaken the finished concrete.

What is the chemical process by which cement sets and hardens into a solid?

Hydration: in cold weather an accelerator is added to speed it up, and the heat the faster reaction gives off helps offset the cold.

How does mortar, used to bond bricks, differ from concrete?

It contains only fine aggregates: mortar is sand, binder and water with no gravel, which gives it a smooth texture a trowel can spread between bricks.

The word 'concrete' comes from a Latin word meaning what?

Compact or condensed: Latin concretus comes from concrescere, 'to grow together', and English took it for things formed of separate parts fused into one solid mass.

Which mid-20th-century architectural style is known for raw, unfinished concrete and bold geometric forms?

Brutalism grew from the postwar need for affordable, functional buildings, so its raw concrete shaped social housing, universities and government offices.

Which ancient desert traders built secret underground cisterns sealed with waterproof lime mortar?

The Nabataeans marked their hidden cisterns with signs only they could read, so the desert itself became their fortress against enemies.

Roman concrete was full of chunky rubble, so how did builders usually put it in place?

Laid it by hand: the rough mix filled the gap between neater faces of brick or stone, which hid the core.

Which Roman building has the world's largest unreinforced concrete dome?

The Pantheon's dome spans about 43 metres; its builders graded the concrete from heavy stone low down to light pumice near the top, easing the load on the dome.

What volcanic ingredient gives Roman concrete its remarkable durability and resistance to seawater?

Pozzolana ash, volcanic ash from around Pozzuoli near Naples, reacts with lime and seawater to form aluminous tobermorite crystals that strengthen the concrete over centuries.

What technique has been proposed as the source of Roman concrete's 'self-healing' ability?

Hot mixing that leaves lime clasts: when water seeps into a crack, the lime dissolves and recrystallises as calcium carbonate, sealing the crack before it spreads.

Why did the US order ships built from concrete during the First World War?

Steel was scarce: but none of the ships the government ordered was finished before the war ended, so they never saw wartime service.

Which Frank Lloyd Wright house in Pennsylvania is famous for its cantilevered concrete terraces?

Fallingwater's cantilevered terraces sagged for decades, so in 2001-02 engineers strengthened them with high-strength steel cables to stop further sagging.

John Smeaton used hydraulic lime in the 1750s to build which English lighthouse?

Eddystone: after cracks appeared in the rock beneath it, the tower's upper part was taken down and rebuilt on Plymouth Hoe.

Who patented Portland cement in 1824?

Joseph Aspdin's cement was not fired hot enough to match modern Portland cement; it was a first step, refined into the modern material in the 1840s.

Why was Portland cement named after Portland?

It looked like Portland stone: the name implied the cement matched the high quality of that widely used English building stone.

Which French gardener patented iron-reinforced concrete plant tubs in 1867 and is usually credited with inventing reinforced concrete?

Joseph Monier sold his patent rights outside France, and German engineer Gustav Adolf Wayss bought the German rights and built companies around the technique.

Which French industrialist built an iron-reinforced concrete house near Paris in the 1850s?

François Coignet put iron in the walls to keep them from spreading or overturning.

Which French engineer patented prestressed concrete in 1928?

Eugène Freyssinet: prestressed concrete is squeezed before it bears loads, so it can form thinner, lighter bridges and roofs than ordinary reinforced concrete.

Portland cement is made by heating limestone with clay or shale and grinding the resulting product with what?

Gypsum is ground in with the kiln product to supply sulfate that slows the early setting reaction, giving crews time to place and finish the concrete.

Why do the steel bars cast inside concrete have ridges along their length?

To stop them slipping: the ridges lock each bar into the hardened concrete. Steel suits the job because it swells and shrinks with temperature about as much as concrete, so the two stay in step through hot and cold.

According to Abrams' law, what does a lower water-to-cement ratio produce?

Stronger, more durable concrete: water the cement doesn't use evaporates as the concrete dries, leaving pores that weaken it.

Fly ash, a common mineral admixture, is a by-product of what?

Coal-fired power plants: fly ash is captured from their flue gases, and reusing it in concrete keeps much of it out of landfills and ash ponds.

Why do builders add tiny air bubbles to concrete?

Frost resistance: the bubbles cut the damage done when water inside freezes, and as a bonus they make the wet mix flow more easily.

Why is calcium chloride, an effective accelerator, prohibited in some countries?

It corrodes steel reinforcement: chloride ions attack the bars, and as the rust expands it cracks the concrete around them.

What is asphalt concrete commonly called in the UK and Ireland?

Tarmac: in 1901 Edgar Hooley noticed that a patch where spilled tar had been covered over stayed dust-free and unrutted, and he patented tar macadam.

Which carmaker's concrete factory in Turin had a test track on its roof?

Fiat: after the factory closed in 1982, Renzo Piano turned it into a centre with shops, hotels and an auditorium.

When a concrete beam sags under a load, which kind of stress acts along its bottom face?

Tension: the underside stretches as the beam sags, and because concrete cracks when stretched, steel bars are cast near the bottom to carry the pull.

Which famous statue is built of reinforced concrete clad in a mosaic of soapstone tiles?

Christ the Redeemer is struck by lightning so often, despite its lightning rods, that a storm in 2014 broke off one of its fingers.

Which dam, dedicated in 1935, was cooled by pipes carrying refrigerated water through its concrete?

Hoover Dam was poured as separate columns of blocks, and once they had cooled, grout was forced into the gaps to join them into one solid mass.

What is a 'tremie'?

A pipe with a hopper for pouring concrete underwater: its lower end stays buried in the fresh concrete, so turbulent water can't wash the cement out of the mix.

Concrete buildings resist fire better than steel frames because concrete has what property?

Lower heat conductivity: heat creeps through concrete slowly, which is why steel frames are sometimes encased in concrete to shield them in a fire.

On average, producing 1,000 kg of cement releases roughly how much CO2?

One tonne, roughly: emissions depend largely on how much clinker goes into each tonne, so cements that swap part of it for other materials cut them.

Which country used more cement in three years than the United States used in the whole 20th century?

China was building new cities, roads, bridges and railways at record speed, and that building boom took mountains of cement.

Heating limestone in a cement kiln drives carbon dioxide out of the rock in which reaction?

Calcination releases CO2 locked in the limestone itself, so switching the kiln to cleaner fuel can't remove that part of cement's emissions.

Which dam holds more concrete than any other dam in the world?

Three Gorges Dam came at a human cost: building it and filling its huge reservoir displaced more than a million people from their homes.

Cutting or grinding concrete releases dust that can cause which lung disease?

Silicosis comes from the crystalline silica in concrete's sand and stone, so crews cut with water sprays or dust extraction to keep the fine dust out of the air.

Which landmark's roof sails are precast concrete shells, all cut from segments of the same sphere?

Sydney Opera House: shaping every sail from one sphere let its concrete ribs be cast in common moulds and mass-produced on site, then lifted into place.

Giant concrete caissons were sunk as breakwaters for the Mulberry harbours in which WWII invasion?

Normandy landings: the harbours were built in Britain and towed across the Channel, so ships could unload in sheltered water in all weathers.

Why do concrete sidewalks have grooves cut across them at regular intervals?

To control where cracks form: concrete shrinks as it dries, and the grooves create weak lines, so cracks tend to form neatly inside the grooves.

ICFs, hollow blocks stacked and filled with reinforced concrete to form walls, are most often made of what?

Polystyrene foam: the forms stay in the finished wall as its insulation, so a single step both shapes the concrete and insulates the wall.

New concrete stays cooler than fresh asphalt in summer sun mainly because it has a higher what?

Albedo: pale new concrete reflects far more sunlight than black asphalt, so paving with light-coloured concrete may help lower a city's temperatures.

Fresh, uncured concrete must be handled with protective equipment because it is what?

Highly alkaline: wet cement is strongly caustic, so skin left in contact can suffer severe burns unless it is promptly washed off with water.

In which English county is the Isle of Portland?

Dorset: despite its name, Portland is not a true island but a tied island, joined to the mainland by the long shingle ridge of Chesil Beach.

Silica fume, an ultrafine powder added to high-performance concrete, is a by-product of making what?

Silicon and ferrosilicon alloys: the fume's particles are about a hundredth the size of cement grains, and their huge surface area makes them react fast, giving very strong concrete.