Thursday, October 24, 2013

Concrete

The Leaf House
After talking about money for the last few posts, I'd like to talk about something more, er, concrete. And what could be more concrete than concrete?

There must be a weird bit of serendipity here – I was just about to begin research on some aspects of architecture, and was thinking particularly about lime. Lime is made from limestone, essentially the skeletons of ancient corals, mollusks and foraminifera that have been compressed by geologic time into rock. Because these skeletons consist mainly of calcium, they are privy to a unique chemical reaction with water  that makes a good part of building possible. This discovery was probably as important to the construction aspect of civilization as the discovery of making bread with yeast was to the culinary aspect.

Dig limestone out of the earth, heat it to over 900 degrees in a kiln, pulverize it, mix it with water, and you have the basis for much of human construction throughout the ages and throughout the world. It's the basis for plaster, stucco, mortar and cement (which are still in use today). And, of course, the Romans added sand, aggregates, water, and pozzolan to cement to form concrete, creating the concrete revolution that defined European building during the Roman Empire. Essentially, these are all taking advantage of the chemical properties of limestone (which we did not understand scientifically until relatively recently) – it forms a paste that hardens almost as solid as rock.

So, after contemplating how important and indispensable this ancient pseudo-rock is to our building and construction abilities, the very day I was look more into it, here is what I saw on Resilience.org:

Burning the Bones of the Earth: Lime Kilns (Low Tech Magazine)

Here's a short history of concrete from concreted.com:
 Concrete is a compound material made from sand, gravel and cement. The cement is a mixture of various minerals which when mixed with water, hydrate and rapidly become hard binding the sand and gravel into a solid mass. The oldest known surviving concrete is to be found in the former Yugoslavia and was thought to have been laid in 5,600 BC using red lime as the cement.

The first major concrete users were the Egyptians in around 2,500 BC and the Romans from 300 BC, in fact the very word 'concrete' is derived from the Latin concretus, meaning grown together or compounded. Most of the surviving roman structures, from the Colosseum to Hadrian's Wall, were constructed using concrete.

The quality of cementing materials deteriorated and even the use of concrete died out during the Middle Ages as the art of using burning lime and pozzolan (admixture) was lost, but it was later reintroduced in the 1300s. In 1414 the manuscripts of the Roman Pollio Vitruvius were discovered in a Swiss monastery reviving general interest in concrete, however it was not until the 1800s and the emergance of Portland cement that the next developments in concrete took place.

Portland cement was first manufactured in Britain in the early part of the 19th century, and its name is derived from its similarity to Portland stone, a type of building stone that was quarried on the Isle of Portland in Dorset, England. The patent for Portland cement was issued to Joseph Aspdin, a British bricklayer, in 1824.

Concrete is now universally the most commonly used construction material for foundations, reinforced frames for buildings, bridge decks, retaining walls, roof tiles, in-situ and precast floors. Most structural concrete is supplied to site as ready mixed concrete. Many modern concretes contain admixtures, such as plasticisers, and pozzolanic additives, such as pulverised-fuel ash or blast furnace slag to enhance the durability or reduce the cost of the concrete.
 More about concrete:

Concrete Being Remixed With Environment in Mind (New York Times)

Researchers develop "biological concrete" for moss-covered walls (Dezeen)

Gengineered concrete-patching bacteria: BacillaFilla (BoingBoing)

Hemcrete®: Carbon Negative Hemp Walls (Inhabitat)

A new generation of designers brings concrete into the home (Slate)

Of course, nothing lasts forever, not even concrete, as numerous Roman ruins can attest. It's particularly vulnerable to freeze-thaw cycles where even after a few decades, concrete is cracking and spalling off of buildings and freeways. But at least they make dramatic ruins. That makes a good segway to these posts from Energy Skeptic:

How long will concrete last if it isn’t maintained?

A Century from Now Concrete Will be Nothing But Rubble

Why is modern concrete falling apart?

3 comments:

  1. Good morning, Expatriate from Wisconsin,

    Since I live in an ocean habitat, I know a thing or two about spalling, the number one problem of concrete. Not concrete itself but the reinforcing rods inside, also known as rebar, are the problem. High salinity causes rebar to corrode around which concrete breaks into chips, fragments and splinters.

    Critters like myself know something about sand. You see, concrete is a mixed marriage of slaked lime and sand - the primary reason why concrete is often vague and indeterminate. When sand marries within the faith, you get glass. The ethnic purity of glass accounts for its transparency, which can be very boring unless adulterated with an alluring mineral.

    Humanoids experience icebergs from above, knowing four-fifths lie hidden below water. For cephalopods, the reverse. When we look up and see a shadowy boat hull, we know that four-fifths are above the water line.

    I rarely experience the pure ethnicity of sand until a boater throws a glass bottle overboard. In my travels across the reef, I use them as motels – simply squeeze myself in and check in for the night at no charge. I prefer 2-liter size Tanqueray bottles. Roomier and more comfortable, they afford me an emerald-green view of the world.

    ReplyDelete
  2. Few days ago suddenly i feeling a problem about rebar .I am always looking for a solution finally i find it this article
    rebar reinforcement

    ReplyDelete
  3. Excellent use of the curable chemical in concrete for satisfactory job provided by curing compound in India has been expand here to increase the benefits in commercial organization. Thanks for giving this ridiculous blog.

    ReplyDelete

Note: Only a member of this blog may post a comment.