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COPYRIGHT 2003 All rights reserved. Reproduced by permission of The Condé Nast Publications Inc.
Some friends of mine--former New Yorkers who had moved to the country--bought a Labrador-retriever puppy. When the dog was six months old, they took her with them on a weekend visit to Manhattan. The dog adored New York's pungent sidewalks, but she hadn't relieved herself since leaving home, and my friends began to worry that she was ill.
The following morning, the dog was almost standing on tiptoe, and my friends suddenly guessed her problem: she had been housebroken in the fieldlike yard behind their place in the country, and to her Manhattan didn't look like outside. Concrete was a form of flooring, as far as she could tell; the pale trees poking through SoHo's sidewalks were more like houseplants than like woods. My friends grabbed her leash and rushed her to Washington Square Park.
Two hundred years ago, a pet with a superego would have had no problem with Manhattan, because it was still mostly forest and field. Metropolitan civilization, such as it was, confined itself to the island's southern tip. A broad salt marsh lay where the East Village lies today. Murray Hill and Lenox Hill were hills. Harlem was a bucolic outpost on a plain flanked by sylvan bluffs.
During the decades that followed, Manhattan's builders levelled the hills, filled the valleys, buried the streams, and imposed an unyielding, two-dimensional grid of avenues and streets. When that grid was conceived, in the early eighteen-hundreds, money entered and left the city by way of the rivers on either side, so the cross streets were laid out close together, to provide maximum access to the piers. The tight spacing left little room for yards or gardens or parks, and, as new buildings rose and multiplied, the sky withdrew. Pavement smothered earth. Soaring rooftops defined a sort of alternate topography, while foundations, sewers, and tunnels gnawed the landscape from below. The old contours receded into the mantle of habitation, and New York became an island of concrete.
Quite a bit of that concrete is plainly visible--in sidewalks, subway platforms, parking garages, bridge abutments, the all-concrete thoroughfares of Sixth Avenue and the West Side Highway, the spiralling shell of the Guggenheim Museum--but much more of it lies beneath the city's surface. On most of Manhattan's streets, asphalt is mainly a veneer applied to a thick, underlying base of concrete. The subfloors of most apartments, offices, and stores are made of concrete, or partly of concrete. The ongoing construction of the Third Water Tunnel, the most ambitious and expensive public-works project in the city's history, has consumed several million tons of concrete since the digging began, in 1970, and will consume many thousand more tons by the time the last of the ancillary branches has been completed, in 2020 or so.
Of all the catalysts of human progress, concrete may be the least prepossessing. If you reckon significance by cumulative mass, however, you could argue that concrete belongs at the top of the list: it's the most widely used man-made building material, and without it modern life would be inconceivable. Concrete is more than just an element of New York's impermeable carapace; it's the matrix that holds the city together.
Contrary to popular usage, "concrete" and "cement" are not synonyms. Sidewalks and foundations are made of concrete, not of cement, although cement is concrete's most important ingredient. The other ingredients are gravel or crushed stone, sand, water, and, optionally, various performance-enhancing additives. The vehicles that most people call cement mixers are actually concrete mixers; cement, like talcum powder, is transported mainly in tank trucks.
The cement in concrete is called portland cement, because Joseph Asp-din, an English bricklayer who is credited with the invention of its earliest version, felt that its color was similar to that of limestone quarried on the Isle of Portland, a peninsula on England's southern coast. Aspdin received his cement patent in 1824. His process involved heating limestone and clay in a kiln until parts of the mixture fused, then grinding the burned and desiccated result into a fine powder. Adding water to the powder yielded a workable paste and initiated a complex chemical process, called hydration, in which the water bonded with compounds of calcium, silicon, aluminum, and iron, and caused the whole thing to lock together in a rigid mass. Wet portland cement doesn't merely "dry," the way mud does; hydration transforms it into a chemically distinct material, which continues to gain strength indefinitely.
Used by itself, portland cement would be a poor building material, because it shrinks considerably as it hardens, and as it shrinks it cracks; a sidewalk made solely of cement wouldn't last very long. (Concrete shrinks and cracks, too, but not as much.) In concrete, the function of cement is to fill voids between pieces of fine aggregate (the sand) and pieces of coarse aggregate (the crushed stone or gravel) and glue everything together. The result is a conglomerate-like artificial...
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