Pumice, Rice husk, Manufactured sand, Slag sand, Powdered glass, Fly ash, Quarry dust, Processed Crushed rock fines, Mersey silt, Sugarcane bagasse ash, Groundnut shell, Cork, Tobacco waste.
Understand the role of aggregate in concrete,
- It should be strong enough (at least stronger than the concrete you want) - weakest phase material
- Its chemistry should not be very reactive - durability and dimensional stability perspective.
- Size and shape should accommodate for rheology and hardened state properties of concrete
- Should cater to early age properties of concrete by providing adequate resistance against shrinkage.
Practically, anything from furnace bottom ash to lightweight pumice can be used as aggregate - it depends on what the specifications for concrete are.