November 15, 2014

I’ve been thinking about concrete lately. Concrete is of course the preeminent construction material of our time. Every day I see concrete being poured somewhere nearby, at intersections being reconstructed in Old San Juan, along the roadway by Playa Escambron as bicycle lanes are installed. As quickly as it is being poured, it is being jackhammered (as along the roadway in back of our building) or ripped (as along the sidewalk across from El Hamburger) out in other places Our friend Mario probably had activities like this in mind when, one morning over coffee at the kiosco, he said Puerto Ricans were good at growing concrete.

Concrete is an interesting material, with a long history. It is really three things mixed together – an aggregate of some sort, a cementing material, and water. The Assyrians and Babylonians used sand as the aggregate and clay as the cement. The English engineer John Smeaton invented the first modern concrete in the late 1700s when he created a concrete that hardened under water. His material was used for, among other things, locks in canals, and probably helped make the Erie Canal possible.  – I know the engineers who built Clinton’s Ditch based their designs on English practice.

Joseph Aspdin, an English bricklayer, mixed clay and ground chalk (limestone, really) in a kiln and produced a cement that, when mixed with aggregate and water, produced a concrete much stronger than previous concoctions. Aspdin’s 1824 discovery, now known as Portland cement, remains the basis for current cement mixes. In 1849, Joseph Monier used wire mesh to reinforce concrete to make more durable flowerpots. He was at the time the gardener in charge of the orangery at the Tuileries Gardens, near the Louvre, and had to move the orange trees into and out of the greenhouses every year. He was looking for something more durable than clay (brittle) or wood (subject to decay), the materials of choice at the time.

Monier’s early successes with his pots led him to start a business which eventually used iron-reinforced concrete (chimenti et fer, to him) for pipes, water storage tanks, stairways, and other structures.

Monier’s business had its ups and downs. He displayed his creations at the Paris Exposition in 1867 and received his first of several patents. He became estranged from his first son who started a competing company; his second son died in a construction accident, when he fell off a scaffold. Napoleon III, in 1870, started the disastrous Franco-Prussian War. Monier’s business was destroyed by a Prussian bombardment, and his horses were stolen and slaughtered for food. He restored his business after the war, generated several more patents, all of which he sold to foreign interests for one-time fees. His construction company went bankrupt in 1890 and he lived in retirement, hounded by tax collectors convinced he was getting royalties from his foreign patents.

Monier’s marriage of iron and concrete was propitious. Concrete is strong in compression (pushing forces), weak in tension (pulling forces); iron just the opposite.  Concrete and iron (later steel) – yin and yang, light and dark, Apollo and Dionysius, Cadmus and Harmonia, push and pull, tension and compression – combine to make a material that is strong, durable, and relatively easy to manipulate.

David Billington, a civil engineering professor at Princeton, is interested in the process by which new technologies are incorporated into engineering practice. He has written on dams (Grand Coulee, Hoover)and the New Deal, thin shell concrete structures, and, germane to this letter, the adoption of cast iron and reinforced concrete (Monier’s chimenti et fer) into late 19^th and early 20^th century construction. His book The Tower and the Bridge describes the transition in terms of opportunities for thinking about structures as forms of public art. Billington moves from the Tower (as in Eifel) to the Bridge (as in Roebling’s Brooklyn) and then to a series of Swiss bridges made of reinforced concrete as examples of structural art. The Swiss, apparently, procure bridges by a less cumbersome process than most countries, allowing their engineers room to be creative in their use of new materials. Billington focused much of his attention on the works of Robert Maillart and his followers.

Why these thoughts on concrete, you ask? Great question. The Shi Long Ling came into port the other day and docked at Pier 14, below our balcony. Unlike most ships entering port here, she was empty, riding high, her bulbous bow almost completely out of water, CHINA SHIPPING BULKER on her side. Puerto Cabella, Venezuela had been her most recent port of call. I have no idea what type of cargo she discharged there. By the way, a bulker is a ship that carries cargo that has to be loaded and unloaded by the ship’s cranes, unlike, for example, tankers and container ships. Compare the Shi Long Ling to the loaded Pacific Basin freighter entering port.

I had been wondering what the piled material next to the pier was. Another ship had docked at Pier 14 last week and discharged a partial load of steel. The fork lifts had to dance their way around the material to stack the steel into neat piles, only to be reloaded onto flatbed trucks.

Now, I’m sure the steel rods are for reinforced concrete, the fer in chimenti et fer. A ship discharging steel arrives in port about every two months, by my informal observations, and most of the steel is in the form of these rebars, as they are inelegantly called – they are after all rods, and not bars. The rebars are trucked to construction sites around the island and, I suspect, transshipped, in smaller vessels, to Caribbean Islands lacking substantial port facilities.

OK, the piled material. It turns out it is concrete, huge chunks of concrete rubble, perhaps from highways or buildings, and the Shi Long Ling is being loaded with it. This is quite a process. First, the front end loaders moved piles of what appears to be sand ship side. You can see one of the piles beneath the S in CHINA SHIPPING BULKER in the image of her. The ship’s cranes lifted it into each of the four holds. Next, the loaders brought buckets of the rubble ship side, which the ship’s cranes lift into the prepared holds. This has been going on for three days now.

This was a truly Sisyphean task. A parade of trucks carrying more rubble arrived, causing the pile to enlarge even while the ship was being loaded. It is as if the rubble was in storage, ready to pounce on the first ship to come take it away.

Who would want concrete rubble, and why? It turns out concrete can be recycled. It is crushed into appropriate particle sizes, and the crushed product is used as aggregate in new concrete mixes, replacing virgin aggregate. By one estimate, 140 million tons (!) of concrete are recycled each year, in the US alone. Using recycled concrete as aggregate apparently results in a concrete product that weighs 10-15% less than concrete made with virgin aggregate, and can cut waste landfill disposal costs, among other alleged benefits

I don’t know where the Shi Long Ling will go next, with her load of concrete rubble for recycling. China? Back to Venezuela? Perhaps one of these days I’ll get on the web and research commodity flows, specifically concrete rubble.

So, the activities I’ve been watching in the port, the steel rebars and the concrete to be recycled, all relate back to the efforts of a Parisian gardener trying to protect his orange trees.

Who knew?

References:

Billington, David. The Tower and the Bridge: The New Art of Structural Engineering. Princeton University Press, 1985.

See Wikipedia entries for concrete, cement, Robert Maillart, and Joseph Monier for more information.