Cob: concrete is forever?

[Eric Straatsma]

I have heard it said by at least one post,  that concrete is a forever
material. I am here to give the opposing viewpoint.  Concrete does decay and
degrade depending on many factors that cannot be controlled 100%. For
example, lets assume that concrete is like a rock. Rocks absorb moisture and
concrete does too. As this moisture freezes and thaws, inside of concrete
pores,  it breaks up the concrete from inside, expanding cracks and breaking
off small pieces. All rocks go through the same process. Nature makes sand
out of rocks eventually.

Second, rocks are subject to heating and cooling stresses, that break up
rocks also. If concrete is heated to 130 during the day and then cooled to
50 degrees at night, it contracts and expands, which causes cracking and
eventually destruction. It takes a long time, but it happens in rocks too.

Third, concrete is subject to chemical weathering, in acid soils especially
or in acid rain areas, just as rocks are. Concrete is not immortal. But then
again, neither are we.


Blessings,
Eric Straatsma
estraatsma at jps.net