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

1. 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 m 3 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).

2. A substrate according to claim 1 , wherein the binder consists of aluminosilicate minerals, selected from natural pozzolans or metakaolin, or industrial inorganic by-products selected from ground granulated blast furnace slag, fly ash or any mixture thereof.

3. A substrate according to claim 1 , wherein the binder consists of 100% ground granulated blast-furnace slag, 100% fly ash, or a mixture of 60% to 100% of slag and 0% to 40% of fly ash.

4. A substrate according to claim 1 , wherein the at least one activator comprises alkaline reagents selected from the group consisting of sodium silicates, sodium metasilicates, sodium hydroxide or a mixture thereof.

5. A substrate according to claim 1 , wherein the ratio between a solid active content of the activator and the total binder content is located between 2 weight % and 8 weight %.

6. A substrate according to claim 1 , wherein a superplastifier is present, in a quantity between 0.12 and 0.8% (m/m) of binder.

7. A method for plant germination and growth comprising placing a seed in or on the Portland cement-free porous rigid mineral substrate according to claim 1 .

8. Method for preparing a Portland cement-free porous rigid mineral substrate as defined in claim 1 , comprising:

a) mixing:

a binder consisting of pozzolanic material;

at least one alkaline activator;

water in an amount effective to provide a water-to-binder ratio between 0.2 and 0.4;

between 1400 kg and 1600 kg of aggregates per m 3 of concrete, said aggregates with Dmax of 4 mm;

whereas the paste volume is between 75 and 120 l/m 3 ;

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);

b) pouring the mix obtained in step a) into a mould;

c) curing the moulded mix; and

d) washing the cement-free porous rigid mineral substrate obtained in step c).

9. Method according to claim 8 , further comprising a step b′) of forming a hole in the moulded mix for seeding, after step b) and before step c).

10. Method according to claim 8 , further comprising the following steps:

e) placing a seed on the surface of the Portland cement-free porous rigid mineral substrate;

f) supplying water or a nutrient solution to the Portland cement-free porous rigid mineral substrate for germination of the seed.

11. Method according to claim 10 , wherein the water or nutrient solution supplied in step f) is maintained at a level of ⅓ to ½ of a height of the substrate.

12. The method according to claim 9 , further comprising the following steps:

e) placing a seed on the surface of the Portland cement-free porous rigid mineral substrate;

f) supplying water or a nutrient solution to the Portland cement-free porous rigid mineral substrate for germination of the seed.

13. The method according to claim 12 , wherein the water or nutrient solution supplied in step f) is maintained at a level of ⅓ to ½ of a height of the substrate.

14. The method of claim 7 , further comprising supplying water or a nutrient solution to the Portland cement-free porous rigid mineral substrate for germination and growth of the seed.

15. The method according to claim 14 , wherein the water or nutrient solution supplied is maintained at a level of ⅓ to ½ of a height of the substrate.