Crushed Concrete,

Expanded Shale,

Pummice,

sea shells,

Basalt

Limestone,

slag

Just about anything that is not organics, or soil, or clay. or silt

Crushed Concrete,

Expanded Shale,

Pummice,

sea shells,

Basalt

Limestone,

slag

Just about anything that is not organics, or soil, or clay. or silt

I was recently in Hawaii.

It is interesting that everything is made from the local Lava Flows.

In fact Lava is the only material available to make Aggregate for concrete,

and for Asphalt. The Asphalt Binder, and the Portland Cement are all

imported, but there is ample Lava Available for aggregates.

If you think about it, concrete is a mixture of inexpensive mined and crushed

materials mixed with an expensive material ( Portland Cement ), and stretched

with a less expensive material ( fly ash ) to hopefully create a durable

product that will last at least one life time ( 50 to 70 years ), or longer.

The Key to durability is rigidity, and dimensional stability of the aggregates.

Aggregates that expand, contract, dissolve, or react with the other

ingredients of concrete will not work, unless you can coat them to

limit the reaction , as fly ash does when it coates aggregates to

limit Alkali-Silica Reactivity.

Crushed aggregates work better than smooth aggregates because they

have a better, cleaner surface area with more locations for the

Portland cement, and the fly ash to bond to the surface of the aggregate.

Clean clear water, free of salts, alkali, acids, oils, etc. is a must for

a good concrete. If you would not drink the water, do not use it in the

concrete.

The better question is what is available locally that will work well as

an aggregate, and is plentiful, and inexpensive, easy to transport,

easy to crush, easy to mix, and is stable for a very long time when

mixed with Portland cement, and Fly ash, and clean water.