[Greenbuilding] concrete vs block vs ___foundation wall

[Rob Tom]

On Tue, 10 Oct 2006 17:32:05 -0400, Bruce Donelson  
<abetterbuilder at frontiernet.net> wrote:

>
> A dry stacked wall might be a tad stronger than a wall with mortar  
> joints.
> You can kick either of them over. All the strength in a block wall comes
> from vertical and horizontal rebar surrounded by concrete.
> Not every cinderblock is made to exact tolerances. A dry-stack wall  
> offers no ability to straighten out a wall as you go

Actually, for a surface-bonded, dry-stacked block wall, you really should  
be using precision-ground block rather than your run-of-the-mill CMU.

As to the strength of a block wall coming from rebar in grouted cores,  
that grouting and rebar is located at the least effective place in the  
wall cross-section for lateral stiffening of the wall.

If the tensile reinforcement (primary steel) is moved out to the surfaces  
of the block and the cement formerly used to make the core grout is also  
moved out to the extreme fibres of the wall section (ie the blocks'  
surface) in the form of a surface-bonding mortar, then the total amount of  
high-embodied energy steel and cement used would be reduced and the wall  
would be stronger (in terms of lateral stiffness) as a result.  (Fibre  
admixtures would still be used in the mortar as secondary (ie temp and  
shrinkage) reinforcement.)

Furthermore, come the end of the block wall's useful service life,  
deconstructing a surface-bonded block wall and salvaging the block for  
re-use would be relatively easy, whereas deconstructiing a  
rebarred/core-grouted CMU wall would likely mean a mess of debris that  
you'd have a hard time even hauling to a landfill without first going at  
it with either dynamite or diamond saws.

And the surface-bonded block would have the cores freed up to enable  
insulation of the cores (for what minimal good  that would do).

Which is the more Green choice ? [Rhetorical question]

Taken one Green step  further, the material from which Durisol ICFs are  
made (mineralised wood fibre wastes), unlike styrofoam-based ICFs, is  
capable of taking significant axial loads so would lend itself to  
surface-bonded walls suitable for residential foundations and walls.


===* ===
Rob Tom
Kanata, Ontario, Canada
<archilogic at chaffyahoo dot ca>
winnow the chaff from my edress in your reply