The history of concrete: from Roman opus caementicium to modern concrete

Photo: interior of the Pantheon dome in Rome, the largest and oldest unreinforced concrete dome still standing. Photo: Livioandronico2013, Wikimedia Commons, licence CC BY-SA 4.0 (cropped)

Building facts #4 · Every Monday and Thursday one building topic, examined in depth 

Concrete is so ordinary that we walk on it, drive over it and live under it without thinking twice. Yet it is one of the oldest high-tech building materials we still use. The Romans mixed lime, volcanic ash and rubble into opus caementicium; centuries later Portland cement, steel reinforcement and prestressing turned that idea into the bridges, locks and floors of today. In this fourth edition of Building facts we look at one topic: the history of concrete. (Missed edition #3? Read the history of the tile, from Delft Blue to porcelain stoneware.)

Where does the word 'concrete' come from, and what is opus caementicium?

The English word concrete comes from the Latin concretum: solidified, grown together (con- + crescere, to grow). Cement goes back via Old French to Latin caementum, hewn stone. The Romans themselves did not use our modern pair of words in the same way; scholars usually call their material opus caementicium, after the caementa — the coarse rubble aggregate packed into the mortar.

Roman concrete was a hydraulic mix: lime mortar with reactive volcanic ash (pozzolana, Latin pulvis puteolanus from the Bay of Naples) and aggregate such as tuff, brick rubble or stone. Vitruvius, writing around 25 BC, recommended one part lime to three parts pozzolana for buildings, and a richer 1:2 ratio for underwater work. The material could set under water, which made harbours possible: the harbour of Caesarea (22–15 BC) is a famous large-scale example. Unlike modern ready-mix, Roman concrete was often laid rather than poured, with larger pieces of aggregate.

From about 150 BC the material was in widespread use. After the fire of Rome in 64 AD, Nero's building code pushed brick-faced concrete, which helped the craft grow. (For fired clay as a facing material, see edition #1: the history of the brick.)

Why is the Pantheon dome still standing?

The most famous Roman concrete structure is the Pantheon in Rome. Its dome, completed around 125–127 CE under emperor Hadrian, is still the world's largest and oldest unreinforced concrete dome. The builders lightened the upper part: near the top the aggregate is light tuff and pumice (about 1,350 kg/m³), while the foundation uses denser travertine (about 2,200 kg/m³). An oculus of about 9 metres lets in light and weather.

Recent research (2023) also points to lime clasts from a hot-mixing technique with quicklime. When water enters a crack, those clasts can help form new calcium carbonate and reseal it — a self-healing effect that helps explain why so much Roman marine concrete still looks solid after two thousand years. Seawater reacting with volcanic ash and lime can even form rare crystals such as tobermorite.

What happened to concrete after the Romans?

With the decline of the Roman world, the quality of cementing materials fell. Between about 1200 and 1500 much of the old know-how of burning lime with pozzolan was lost or only partly remembered. Builders went back to ordinary lime mortars that do not set under water in the same way.

The comeback started in the eighteenth century. In 1793 John Smeaton found that limestone containing clay produced a lime that hardened under water — hydraulic lime — and used it to rebuild the Eddystone Lighthouse. In 1796 James Parker patented a natural hydraulic cement from calcined clayey limestone nodules, sold as Parker's Cement or "Roman cement". In France, Louis Vicat later made artificial hydraulic lime by calcining synthetic mixes of limestone and clay (1812–1813).

Who invented Portland cement?

On 21 October 1824 the Leeds bricklayer Joseph Aspdin was granted British patent BP 5022 for "An Improvement in the Mode of Producing an Artificial Stone". He called the product Portland cement because the set mortar looked like the fine building stone from the Isle of Portland. His process burned limestone (even road sweepings) with clay, then ground the result to a powder.

Aspdin's early product was not yet identical to modern Portland cement: it was fired at a relatively low temperature and aimed at stucco and mouldings. His son William Aspdin later burned hotter mixes and ground the hard clinker, which is closer to the cement we pour today. By the mid-nineteenth century Portland cement was being imported into the Netherlands as well, including for the concrete-filled piers of the iron railway bridge over the IJssel at Westervoort in 1856.

How does modern concrete actually harden?

Modern concrete is a composite: cement + water form a paste that binds aggregate (sand and gravel). Typical mixes are roughly 7–15% cement, 60–75% aggregate and 14–21% water by volume, sometimes with entrained air. Cement is not glue that dries; it is a hydraulic binder. When you add water, the calcium silicates in Portland cement react in a process called hydration. They form calcium silicate hydrate (C-S-H) and calcium hydroxide. The interlocking C-S-H gel is what gives concrete its strength.

Concrete does not need to dry out to harden — it needs moisture to keep hydrating. Too much mix water leaves more pores and weakens the concrete; too little makes it unworkable. Strength is often checked at 28 days, but hydration can continue for years if water is still available. That chemistry is why a bag of sand-cement only works when you dose water carefully — we explain bag counts in how many bags of sand-cement do I need?, without repeating the calculator here.

How did steel change concrete? Reinforced and prestressed

Concrete is strong in compression but weak in tension. In the 1840s–1860s French gardeners and builders started embedding iron mesh in cement. Joseph Monier showed reinforced containers at the Paris Exposition of 1867 and received his first patent on 16 July 1867 for iron-reinforced horticultural troughs. Patents for pipes, panels, bridges and beams followed; in 1875 he designed the first iron-reinforced concrete bridge at the Château de Chazelet in France.

François Hennebique turned the idea into a building system. In 1892 he patented a monolithic reinforced-concrete method that combined columns, beams and slabs. Between 1892 and 1902 more than 7,000 structures were built with his system under licence.

Prestressing went a step further. Eugène Freyssinet studied creep in concrete and, in 1928, patented prestressed concrete: high-strength steel put permanently in tension so the concrete stays compressed. His rescue of the Le Havre maritime station in the 1930s made the method famous. Prestressed beams and decks are why long-span bridges and slim floors became practical.

How did concrete arrive in the Netherlands?

Dutch builders already knew volcanic tras (ground tuff) as a hydraulic addition to lime. Home-grown "kunstcement" experiments in the late eighteenth century lost out to imported Portland cement in the mid-nineteenth century. Reinforced concrete entered via Belgium: the Picha brothers held the Monier patent there, opened a branch in Sas van Gent in 1888, and in July 1890 the Amsterdamsche Fabriek van Cement-ijzerwerken (Systeem Monier) was founded. The first larger reinforced-concrete bridge in the Netherlands was the Schollenbrug in Amsterdam in 1900.

Waterworks drove the next leap. The Noordersluis at IJmuiden, opened in 1929, is 400 m long, 50 m wide and 15 m deep — a landmark of early large-scale reinforced concrete in Dutch hydraulic engineering. After the 1953 flood, the Delta Works made reinforced concrete indispensable for dams, locks and storm-surge barriers. You can still see real Roman concrete closer to home too: the Thermenmuseum in Heerlen shows opus caementicium from the Roman baths.

What kinds of concrete do we use today?

Most everyday concrete is still Portland-cement concrete, often delivered as ready-mix from a plant. Admixtures change behaviour: air-entraining agents improve freeze–thaw resistance (from the 1930s), and superplasticizers (from the 1980s) make mixes flow with less water.

Self-compacting concrete (SCC) was proposed by Okamura in Japan in 1986; a prototype was completed at the University of Tokyo in 1988. It fills formwork under its own weight, without vibration. Ultra-high-performance concrete (UHPC) grew from low-porosity paste research and densified-particle mixes; commercial use started in the 1990s, often with steel fibres and a very low water–binder ratio.

And on walls and floors at home you also meet the look of concrete: cement-look porcelain tiles that mimic a poured slab. That is a design choice, not a structural one — for tiling itself, see edition #3 on the history of the tile.

What are some fun facts about concrete?

• The Pantheon dome is still the largest unreinforced concrete dome in the world, almost nineteen centuries after it was finished.
• Vitruvius already prescribed different lime–pozzolana ratios for dry buildings and underwater work — a Roman mix design.
• Aspdin named Portland cement after a stone, not a place where the cement was made.
• Monier's first patents were for flower pots and garden basins; bridges and beams came later.
• The Noordersluis at IJmuiden (1929) is 400 × 50 × 15 metres — larger than many people expect for a lock of that age.
• Self-compacting concrete was invented to keep quality high when fewer skilled workers were available to vibrate every corner of the formwork.

What do you need when you work with concrete or cement today?

You rarely cast a Pantheon in the garden, but the same materials still turn up as screeds, repairs, cores and fixings. Below are a few products that fit that story. How many sand-cement bags you need is calculated in our sand-cement guide; drilling dense concrete is covered in diamond drilling in tile, concrete and masonry; choosing plugs and anchors for concrete is in fixing into concrete, brick and aerated concrete.

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Frequently asked questions about the history of concrete

Building facts takes one building topic under the magnifying glass every Monday and Thursday. This is edition #4. Read the previous edition too: the history of the tile, from Delft Blue to porcelain stoneware, and edition #1: the history of the brick. Fun link: Roman walls were often brick-faced concrete — clay and concrete side by side.