Cement-free porous substrate for plant germination and growth made of alkali-activated pozzolans

A Portland cement-free porous rigid mineral substrate, with a final compressive strength after hardening between 3 MPa and 10 MPa and porosity between 25% and 35%, comprising:

• a binder consisting of pozzolanic material;
• at least one alkaline activator;
• a water-to-binder ratio between 0.2 and 0.4;
• a paste volume between 75 and 120 l/m;
• between 1400 kg and 1600 kg of aggregates per m3 of concrete, said aggregates with Dmax of 4 mm,
• whereas the aggregates have a D90/D10 comprised between 1 and 3.5, whereas D90 is selected to be between 3 and 3.5 mm and the D10 is equal or larger than 1-0.5 mm, the aggregates being characterized wherein a natural packing solid is between 55% and 65% (v/v).