Why is modern concrete falling apart?

Here’s more information from Courland’s book “Concrete Planet” and other information I found on the web since I wrote Enough energy after Peak Oil to rebuild and repair concrete infrastructure?

It appears there’s very little testing of projects later on to see how they stood up over time to wear and tear.

It wasn’t until 1987 that engineers discovered the so-called “high strength” concrete used since 1930 was far worse than the concrete before then — buildings, roads, and other structures were falling apart over twice as fast as pre-1930 concrete structures.

This happened because “High Strength” (Portland) concrete gets strong much faster than pre-1930 concrete, greatly speeding up the time it takes to build a structure.

Why and how does “high strength” modern concrete crack and erode (which lets water in, eventually rusting out the rebar inside, ruining the structure)?

  • Annual freeze and thaw cycle, freezing of trapped water
  • Expansion of aggregates
  • Erosion by fast-flowing water
  • Vibrations and loads on bridges
  • Wind pressure sways and oscillates concrete buildings – cracks result
  • Deterioration by surface wear: Abrasion, Erosion, and Cavitation
  • Cracking:from crystallization of salts in pores, drying shrinkage, thermal contraction
  • Radiant heat
  • Deterioration by Frost Action
  • Fire
  • Chemical: carbonatation, chlorides, sulfates Corrosion of steel, Alkali-silica reaction, Sulfate attack, Delayed ettringite formation, Acid attack

Concrete statistics

  • 40 tons of concrete for every person on the planet, plus 1 ton per person per year added (7.5 billion cubic meters of concrete made per year)
  • 100 million years from now, crushed and recrystallized concrete will leave a rust-colored layer of sediment
  • First skyscraper 1891 Monadnock Building in Chicago, the tallest brick masonry structure and commercial building, the first to use aluminum for staircases. 17 stories, 214 feet high.  The word skyscraper comes from the name for the tallest sail on clipper ships (page 228).
  • 1891 also first concrete street (in Bellefontaine, Ohio).
  • American Interstate Highway System (1956-1992) largest use of concrete in any civil engineering project until then.
  • Then steel frames possible, the end of brick masonry buildings.
  • We might all be living in concrete homes now if Edison hadn’t messed up so badly (chapter 7)
  • US dams are on average 52 years old, it could cost over $52 billion to rehabilitate them

Concrete and Earthquakes

  • “Concrete lobbyists twisted the data [after the 1906 San Francisco earthquake and fire] to prove that reinforced concrete had stood up well…because of this deception, many people around the world would die in the course of the following century to buildings that they thought were immune to collapse from the violent movements of the earth”. Page 305, more details on pages 313-317.
  • Brick on the other hand, had a bad reputation, but recent research has shown that well-built brick structures did well in the 1906 earthquake (page 315).

Concrete and Fire

  • Concrete is not fireproof, but you’re less likely to be injured than in a wood structure, and have more time to escape
  • Brick, on the other hand, is born in fire, and immune to all but “insanely high temperatures”, this is why bred and pizza ovens are made of brick – if they were concrete they’d fall apart.

A world without concrete: Smaller and shorter buildings, more brick buildings, dams made of earth or huge blocks of stone, road surfaces rough except after recently applied newt layer of asphalt, lots of potholes

Further reading

If you’re interested in what a wood based society is like and what it’s capable of, read John Perlin’s outstanding “A Forest Journey: The Role of Wood in the Development of Civilization”.

To see how fast the world would crumble if we weren’t around (or there were far fewer of us): Alan Weisman “The World Without Us” and How long will concrete last if it isn’t maintained?

Andrea Hamilton. 6 march 2014. Concrete conservator. Nature.

 

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One Response to Why is modern concrete falling apart?

  1. Jan Steinman says:

    It would be interesting to see natural building materials — cob, straw bale, light clay, etc. — compared to brick and concrete.

    Some cob-and-thatch houses in England have been continuously occupied for 500 years. Of course, that implies they had maintenance, which is the point, no?