Multi-layer slab product made of stone granulates and relative manufacturing process

A multi-layer composite slab, comprising:

• first and second dense layers of a first material agglomerate and a first binding agent;
• and
• an expanded material layer in compressive direct contact with the first and second layers and intermediate the first and second layers, the second layer being of an expanded material agglomerate and a second binding agent,
• the first and second dense layers being surface layers, and
• the expanded material layer being less dense than each of the first and second dense layers.

A method of preparing a multi-layer composite slab product, comprising the steps of:

• surrounding a pre-cast support made of an expanded agglomerate and a first binding agent within a mixture of stone agglomerates and second binding agent;
• and
• vibro-compressing, in a single step, the mixture of stone material agglomerates and second binding agent, wherein
• a multi-layer composite slab is formed comprising
• first and second dense layers of the stone material agglomerates and second binding agent sandwiching the pre-cast support,
• the pre-cast support being an expanded material layer in direct contact with the first and second layers and intermediate the first and second layers,
• the first and second dense layers being surface layers, and
• the expanded material layer being less dense than each of the first and second dense layers.