Concrete block vs brick for RMH bell mass

Assuming I keep concrete out of the extreme heat areas adjacent to the J-tube and just above it can I use concrete block for the mass material in a bell?  I am having trouble finding brick locally.  I've found some brick 100 miles away and even farther.  Hauling that distance is a no go.

I can find brick locally but they're all paving brick and concrete rather than clay.

Most concrete blocks are quite  porous so they contain air, unlike brick that is solid and dense, this means a brick will hold more heat for longer.
You can sometimes find high density concrete blocks that are used to support steel girders, these blocks are made from vibrated 6-1 concrete mix are are very dense, however, they will cost twice as much!
So basically standard concrete blocks are not the best choice but vibrated concrete is fine.

Tim,

Solid clay bricks would be the best, but if I had to use concrete blocks I would fill them with clay/sand mix: mix dry ingredients and add small amount of water, just enough to compact it in the block cavity. Small amount of water will prevent excess shrinkage and cracking.
If you don't have access to clay, just use soil (deeper layer, without organic matter).

Cristobal Cristo wrote:Tim,

Solid clay bricks would be the best, but if I had to use concrete blocks I would fill them with clay/sand mix: mix dry ingredients and add small amount of water, just enough to compact it in the block cavity. Small amount of water will prevent excess shrinkage and cracking.
If you don't have access to clay, just use soil (deeper layer, without organic matter).

to reiterate "the fill"    you can easily tell the difference of 4 parts fine sand to 1 part clay, vs 4 parts clay to one part sand,  And to make it even better (heavy-dense-better mass) use a bit of water glass (sodium silicate) and you will get a mix that is HEAVY, Very DENSE (same thing) and low shrinkage. All win win for mass.

Hi Tim,
Using brick is a natural first choice for its ease of use, uniformity and stackability, but depending on your goals, don't forget that a bell is mostly just a hollow container with mass.
Half barrels or recycled steel cabinets / tanks can be covered with rocky cob.
Or even flat dense stones without the form can make for an interesting bell.
That was how I did mine years back. Very low budget but worked great.