We ran some experiments to see the effects of adding Portland cement to a few batches
of blocks, and I thought I would share the results even before we get the good ones
professionally tested for compression and modulus of rupture. There are a good many
block manufacturers that discourage stabilization with either lime or cement. We have
had no luck with lime stabilization, but cement stabilization is another breed of cat.
We mixed 10% cement by weight into enough clay/sand soil to make about 50 blocks at
2200 psi. We knew it would rain and then freeze right after we did this. Anyways, it’s all
good for experience! The blocks that we now label “stabilized” hold anywhere from 5-
10% Portland cement tilled into about 40% clay and sand with water content held steady
for both stabilized and un-stabilized blocks. We also held the pressure the same. The
results are self-evident.
The answer to the question whether to stabilize or not is rather obvious when you see the
two pictures below comparing the effects of over 6 inches of rain on fresh blocks.
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| stabilized blocks after 6 inches of rain |
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| unstabilized blocks after 6 inches of rain |
Only
48 hours after pressing, we had 5 days of steady rain and then freezing for two nights.
In the picture of un-stabilized blocks on the conveyor, you can see how much
erosion (called spalling) occurred in the week of rain. They are misshapen, although perhaps not as badly as you might think for being virtually
underwater for a week. One point: don’t use these in any house you intend to sleep in.
The first picture shows a pile of stabilized block under the same conditions. They are
still clean with very little spalling and very, very hard—maybe harder for the drenching!
Stabilizing blocks with Portland made all the difference. Later, I will present what
appear to be even more advantages to 10% stabilization. Stay tuned for those statistics
and test results for the stabilized block.
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