I used to sink pallets in my early fishin days...

I was lucky in that there is a state transportation department office very near me...

They have a pile of concrete "test samples"....that weigh about 20 lbs...

These "test samples" are made when the state is building a concrete project (bridge) which requires them to test the crush strength in every concrete truck that delivers to that state project....

The "test samples: fit very neatly in the slats of the pallets...