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Concrete strength of compression.

Concrete strength of compression.

New to forum, not sure where to post this question- product is an 8x8x12 inch solid block, manufactured with the 12 inch dimension horizontal. Will it have the same compression strength horizontally as vertical? Thanks, 4evrjarhead.

RE: Concrete strength of compression.

It should as long as your process doesn't introduce some form of orthotropic properties.


RE: Concrete strength of compression.

For an 8x8x12 sample would test lower if the 12" dimension is vertical compared to a test with the 8" dimension vertical. - Both would have shear failure. The increased friction on the horizontal surfaces of the 8" high test a little more like a confined compression sample.

Depending on the testing machine, there could be some effects if a platen plate is used and it can deflect and concentrate the load in the center of the sample.

I ran into this with some 2 block high 12" CMU prism samples showed a false compressive strength for the lab existing equipment.

The testing machine was only a 200,000 T-O and the lab used a thinner platen because of the usual vertical opening. They installed a thicker, more rigid platen and test results were about 20% higher.

If I have not requested photos for the failure mode, it could have been passed over as a failure to meet the specifications. The designing/spec writing firm was a little embarrassed even though the testing procedure the testing of a 12x16x16 solid sample.


Engineer and international traveler interested in construction techniques, problems and proper design.

RE: Concrete strength of compression.

Thanks for the added info... I would have thought that the failure modes would be similar considering the 'squat' shaped specimen.


RE: Concrete strength of compression.

Thanks for the quick replies. The product info that I supplied should have been 6x6x12 solid block. Would this change the outcome? What I am trying to determine is whether or not the manufacturing position(12" dimension horizontal or vertical) will affect the compression strength. Thanks again, Don.

RE: Concrete strength of compression.

6x6x12? - Could this be for shielding in a nuclear power plan or just for mass and sound proofing somewhere? I have seen thousand of 6" solid block used to build thick walls. - The solid units are light enough the be handled/lifted, but a hand clamp is used for grasping and picking up.

No change in the wall strength due to testing orientation. As far as the manufacturing, 99% of the time the 12" would be a horizontal dimension because of the manufacturing methods and equipment used. The failure mode is not dictated by the manufacturing orientation.

There is a different failure mode between lab testing and actual installed units. The masonry units in a wall are generally controlled by the dimensions of a panel with everything gravitating toward the proverbial 45 degree line, except for flexure. - Once mortar is involved the individuality of the masonry units are converted to a panel. - The strength properties of he mortar has very little effect on vertical loads or flexure.

Just to confuse things, hollow CMUs are always laid the the bottom side(as manufactured) face up. - Easier to handle and spread mortar on.


Engineer and international traveler interested in construction techniques, problems and proper design.

RE: Concrete strength of compression.

thought it was 8x8x12...


RE: Concrete strength of compression.

Shrinkage, dik.

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