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

Abstract

The present invention concerns a Portland cement-free porous rigid mineral substrate made of alkali-activated pozzolans, a method for preparing the same, and use of said substrate to optimize plant germination and growth.

Claims

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.sup.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.sup.3 of concrete, said aggregates with Dmax of 4 mm; whereas the paste volume is between 75 and 120 l/m.sup.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.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 represents the germination rate using three different washing liquids (water, modified Hoagland solution and Hoagland solution).

(2) FIG. 2 represents the pH profile for the three different washing liquids (water, modified Hoagland solution and Hoagland solution).

(3) FIG. 3 represents the electrical conductivity profile for Example 1.

(4) FIG. 4 represents the germination rate between GGBS and Fly Ash type C.

(5) FIG. 5 represents the evolution of pH during plant growth between GGBS and Fly Ash type C.

(6) FIG. 6 represents the germination rate between 2/3.2 mm and 8/11 mm aggregates.

(7) FIG. 7 represents the germination rate between GGBS and OEM based substrates.

(8) FIG. 8 represents the evolution of pH between GGBS and OEM based substrates during plant growth.

EXAMPLES

Example 1

(9) Three porous substrates were manufactured using the same mix design:

(10) TABLE-US-00005 TABLE 5 Mix design for the three porous substrates Binder (Slag) 187 kg/m.sup.3 w/b 0.3 Activator NaOH 50% m/m 3.7% (m/m) Activator Na.sub.2SiO.sub.3 40% m/m 5.2% (m/m) Gravel (2/3.2 mm) 1478 kg/m.sup.3 Paste volume 120 l/m.sup.3

(11) TABLE-US-00006 TABLE 6 Chemical composition and fineness of ground granulated blast furnace slag by X- ray Fluorescence SiO.sub.2 (%) 33.98 Al.sub.2O.sub.3 (%) 14.70 Fe.sub.2O.sub.3 (%) 1.46 CaO (%) 42.08 MgO (%) 3.97 SO.sub.35 (%) 1.63 Na.sub.2O (%) 0.18 K.sub.2O (%) 0.31 TiO.sub.2 (%) 0.58 P.sub.2O.sub.5 (%) 0.02 Mn.sub.2O.sub.3 (%) 0.34 LOI 950 C. (%) −0.87 Sum (%) 98.37 D10 (μm) 3.2 D50 (μm) 13.9 D90 (μm) 37.8 45 μm retained (%) 6.21

(12) The ingredients were mixed until uniform before being poured into three different moulds. The moulds had a cubic shape, each had 4 cm.sup.3 of volume. The samples were steam cured at 60 to 70° C. for 8 to 16 hours and placed in the curing chamber for 7 days before demoulded.

(13) The substrates were then washed in the following 3 different solutions, as described in step d) “Still Cold Wash”: 1. one substrate was washed with Hoagland nutrient solution (treatment 1), 2. the second substrate was washed with a modified Hoagland nutrient solution with an increased concentration of KH.sub.2PO.sub.4 (1.1 mol/L) (whereas the KH.sub.2PO.sub.4 concentration in the traditional Hoagland nutrient solution is 1M) (treatment 2) 3. and the third substrate was washed with water (treatment 3).

(14) The substrates were then seeded according to step e) and germinated according to step f) for a period of 28 days in their respective washing solution (substrate 1 was soaked in Hoagland nutrient solution, substrate 2 was soaked in Modified Hoagland solution and substrate 3 was soaked in water). For the substrate 3, Hoagland solution was introduced only at day 7 to guarantee sufficient nutrients. The germination rate (FIG. 1), pH (FIG. 2) and EC (FIG. 3) were monitored over time.

Example 2—Different Binder: Using Fly Ash C

(15) Porous substrates were manufactured using the following mix design:

(16) TABLE-US-00007 TABLE 7 Mix design for the three porous substrates Binder (Fly Ash - C) 183 kg/m.sup.3 w/b 0.29 Activator NaOH 50% m/m 6.9% (m/m) Activator Na.sub.2SiO.sub.3 40% m/m 10.2% (m/m) Gravel (2/3.2 mm) 1455 kg/m.sup.3 Paste volume 120 l/m.sup.3

(17) TABLE-US-00008 TABLE 8 Chemical composition and fineness of fly ash type C by X- ray fluorescence SiO.sub.2 (%) 36.49 Al.sub.2O.sub.3 (%) 19.41 Fe.sub.2O.sub.3 (%) 6.10 CaO (%) 23.53 MgO (%) 5.10 SO.sub.3 (%) 1.00 Na.sub.2O (%) 3.05 K.sub.2O (%) 0.46 TiO.sub.2 (%) 1.49 P.sub.2O.sub.5 (%) 0.73 Mn.sub.2O.sub.3 (%) 0.03 LOI 950 C. (%) 0.99 Sum (%) 99.71 D10 (μm) 1.9 D50 (μm) 12.9 D90 (μm) 66.0 45 μm retained (%) 17.66

(18) The ingredients were mixed until uniform before being poured into the moulds. The moulds had a cubic shape, each had 4 cm.sup.3 of volume. The samples were steam cured at 60 to 70° C. for 8 to 16 hours and placed in the curing chamber for 7 days before demoulded. After the porous substrate has been washed according to the procedure described in example 1, using Hoagland solution (treatment 1), two seeds are planted by square inch area or species spacing dependent. The Hoagland nutrient solution level was maintained at ⅓ of the height of the substrate to ensure solution throughout the substrate at all times by capillarity when plants are being grown.

(19) Germination rate as compared to the GGBS based substrates was comparable as shown on FIG. 4 below, although maximum reached was about 90%. FIG. 4 shows the germination rate after the soaking step f), wherein time 0 is the day when the seeds were placed on the substrate.

(20) pH also appeared to be similar than GGBS, ranging between 8 and 10 as described on FIG. 5.

Example 3—Aggregates with Bigger Size

(21) Porous substrates were manufactured using the following mix design:

(22) TABLE-US-00009 TABLE 9 Mix design for the three porous substrates Binder (Slag) 182 kg/m.sup.3 w/b 0.35 Activator NaOH 50% m/m 3.7% (m/m) Activator Na.sub.2SiO.sub.3 40% m/m 5.2% (m/m) Gravel (8/11 mm) 1400 kg/m.sup.3 Paste volume 120 l/m.sup.3

(23) TABLE-US-00010 TABLE 10 Chemical composition and fineness of ground granulated blast furnace slag by X- ray diffraction SiO.sub.2 (%) 33.98 Al.sub.2O.sub.3 (%) 14.70 Fe.sub.2O.sub.3 (%) 1.46 CaO (%) 42.08 MgO (%) 3.97 SO.sub.35 (%) 1.63 Na.sub.2O (%) 0.18 K.sub.2O (%) 0.31 TiO.sub.2 (%) 0.58 P.sub.2O.sub.5 (%) 0.02 Mn.sub.2O.sub.3 (%) 0.34 LOI 950 C. (%) −0.87 Sum (%) 98.37 D10 (μm) 3.2 D50 (μm) 13.9 D90 (μm) 37.8 45 μm retained (%) 6.21

(24) The ingredients were mixed until uniform before being poured into the moulds. The moulds had a cubic shape, each had 4 cm.sup.3 of volume. The samples were steam cured at 60 to 70° C. for 8 to 16 hours and placed in the curing chamber for 7 days before demoulded. After the porous substrate has been washed according to the procedure described in example 1 (treatment 1), using Hoagland solution, one or two seeds are planted by square inch area or species spacing dependent. The Hoagland nutrient solution level was maintained to ensure solution throughout the substrate at all times by capillarity when plants are being grown.

(25) Germination rate with 8/11 mm aggregates showed a significant decrease in efficiency (FIG. 6) as compared to the use of 2/3.2 mm aggregates, which could be related to the capillarity absorption and water retention of the substrate, as shown on Table 11. Due to the bigger void size, the water is not retained by the porous substrate and cannot support the germination and growth of the seeds. Only the germination can be supported by the nutrient already provided in the seeds, but after 7 days, the plants started to die by lack of water and nutrients in the porous structure, since capillarity could not occur due to the big size of the pores. Such performance renders the use of bigger size aggregates, above 4 mm, incompatible with hydroponic systems. FIG. 6 shows the germination rate after the soaking step f), wherein time 0 is the day when the seeds were placed on the substrate. Germination with 2/3.2 mm has reached a plateau, which means that more than 95% of the seeds have not only germinated but have continued to develop, reaching a growing stage.

(26) TABLE-US-00011 TABLE 11 Water absorption, retention and drained for porous substrates (measured on 110 × 220 mm cylinder samples) Aggregate size 2/3.2 mm 8/11 mm Water Absorption (%) 34 34 Water Retained (%) 10 3 Water Drained (%) 23 31

(27) To determine “Water Absorption”, “Water Retained” and “Water Drained”, cylinders of 11×22 mm of the same porous material as the substrates, have been manufactured. The substrates are first weighted when totally dry and the water absorption is measured according to norm ASTM C 1745. After all the voids have been filled with water, the cylinders are rapidly removed from the liquid. Water starts pouring from the cylinder, due to its open porosity, and this water is directly collected and measured, leading to “Water Drained”. When no more water pours out, the cylinder is again weighted. The difference between this wet cylinder and the dried cylinder leads to “Water Retained”.

Example 4—Aggregate Below 4 mm, but Having 090-D50-D10 Outside the Invention Scope

(28) Porous substrates were manufactured using the following mix design:

(29) TABLE-US-00012 TABLE 12 Mix design for the three porous substrates Binder (Slag) 149 kg/m.sup.3 w/b 0.35 Activator NaOH 50% m/m 3.7% (m/m) Activator Na.sub.2SiO.sub.3 40% m/m 5.2% (m/m) Gravel (0.3/0.9 mm) 1489 kg/m.sup.3 Paste volume 99 l/m.sup.3

(30) TABLE-US-00013 TABLE 13 Chemical composition and fineness of ground granulated blast furnace slag by X- ray diffraction SiO.sub.2 (%) 33.98 Al.sub.2O.sub.3 (%) 14.70 Fe.sub.2O.sub.3 (%) 1.46 CaO (%) 42.08 MgO (%) 3.97 SO.sub.35 (%) 1.63 Na.sub.2O (%) 0.18 K.sub.2O (%) 0.31 TiO.sub.2 (%) 0.58 P.sub.2O.sub.5 (%) 0.02 Mn.sub.2O.sub.3 (%) 0.34 LOI 950 C. (%) −0.87 Sum (%) 98.37 D10 (μm) 3.2 D50 (μm) 13.9 D90 (μm) 37.8 45 μm retained (%) 6.21

(31) The ingredients were mixed until uniform before being poured into the moulds. The moulds had a cubic shape, each had 4 cm.sup.3 of volume. The samples were steam cured at 60 to 70° C. for 8 to 16 hours and placed in the curing chamber for 7 days before demoulded. After the porous substrate has been washed according to the procedure described in example 1, using Hoagland solution, one or two seeds are planted by square inch area or species spacing dependent. The Hoagland solution level was maintained to ensure liquid throughout the substrate at all times by capillarity when plants are being grown.

(32) When aggregates with a size 0.3/0.9 mm were used, germination rate proved to be very similar to the one when 2/3.2 mm aggregates were used in the sense that all seeds developed successfully. However, none of the roots grew through the porous substrates and only developed from the outer layer, due to the very low size of the voids. The growth of the plants was allowed by a higher water retention that provides sufficient amounts of water and nutrients on the surface of the substrates. (see table 14)

(33) TABLE-US-00014 TABLE 14 Water absorption, retention and drained for porous substrates (on 11 × 22 cm cylinder) Aggregate size 2/3.2 mm 0.3/0.9 mm Water Absorption (v/v %) 34 37 Water Retained (%) 10 21 Water Drained (%) 23 15

Example 5—Cement Based Material

(34) Porous substrates were manufactured using the following mix design:

(35) TABLE-US-00015 TABLE 15 Mix design for the three porous substrates Binder (CEM I 52.5R) 111 kg/m.sup.3 w/b 0.35 Superplasticizer 1.5% (m/m) Gravel (2/3.2 mm) 1500 kg/m.sup.3 Paste volume 75 l/m.sup.3

(36) TABLE-US-00016 TABLE 16 Chemical composition and fineness of CEM I 52.5R used by X- ray diffraction SiO.sub.2 (%) 19.46 Al.sub.2O.sub.3 (%) 4.71 Fe.sub.2O.sub.3 (%) 2.50 CaO (%) 63.55 MgO (%) 2.01 SO.sub.3 (%) 2.63 Na.sub.2O (%) 0.07 K.sub.2O (%) 0.99 TiO.sub.2 (%) 0.30 P.sub.2O.sub.5 (%) 0.26 Mn.sub.2O.sub.3 (%) 0.05 SrO (%) 0.08 Cr.sub.2O.sub.3 (%) 0.01 ZnO (%) 0.02 LOI 950 C. (%) 3.10 Cl (%) 0.01 Sum (%) 99.75 D10 (μm) 3.2 D50 (μm) 13.0 D90 (μm) 33.8 45 μm retained (%) 3.66

(37) The ingredients were mixed until uniform before being poured into the moulds. The moulds had a cubic shape, each had 4 cm.sup.3 of volume. The samples were steam cured at 60 to 70° C. for 8 to 16 hours and placed in the curing chamber for 7 days before demoulded. After the porous substrate has been washed according to the procedure described in example 1, using Hoagland solution, one or two seeds are planted by square inch area or species spacing dependent. The Hoagland solution level was maintained to ensure liquid throughout the substrate at all times by capillarity when plants are being grown.

(38) Germination rate as compared to the GGBS based substrates was significantly lower (<50%), and this due to the high pH (>12) released from the cement matrix rich in calcium ions (FIGS. 7 and 8). Germination was much slower for the cement based substrates and while some seed died, some other started to germinates, thus explaining the variation of the germination curve.

Example 6—Optimized Substrate with Radish

(39) Porous substrates were manufactured using the following mix design:

(40) TABLE-US-00017 TABLE 17 Mix design for the three porous substrates Binder (Slag) 187 kg/m.sup.3 w/b 0.3 Activator NaOH 50% m/m 3.7% (m/m) Activator Na.sub.2SiO.sub.3 40% m/m 5.2% (m/m) Gravel (2/3.2 mm) 1478 kg/m.sup.3 Paste volume 120 l/m.sup.3

(41) TABLE-US-00018 TABLE 18 Chemical composition and fineness of ground granulated blast furnace slag by X- ray diffraction SiO.sub.2 (%) 33.98 Al.sub.2O.sub.3 (%) 14.70 Fe.sub.2O.sub.3 (%) 1.46 CaO (%) 42.08 MgO (%) 3.97 SO.sub.35 (%) 1.63 Na.sub.2O (%) 0.18 K.sub.2O (%) 0.31 TiO.sub.2 (%) 0.58 P.sub.2O.sub.5 (%) 0.02 Mn.sub.2O.sub.3 (%) 0.34 LOI 950 C. (%) −0.87 Sum (%) 98.37 D10 (μm) 3.2 D50 (μm) 13.9 D90 (μm) 37.8 45 μm retained (%) 6.21

(42) The ingredients were mixed until uniform before being poured into the moulds. The moulds had a cubic shape, each had 4 cm.sup.3 of volume. The samples were steam cured at 60 to 70° C. for 8 to 16 hours and placed in the curing chamber for 7 days before demoulded. After the porous substrate has been washed according to the procedure described in example 1, using a modified Hoagland solution, one or two seeds are planted by square inch area or species spacing dependent. The Hoagland solution level was maintained to ensure liquid throughout the substrate at all times by capillarity when plants are being grown.

(43) The plant growth, by means of the fresh and dry mass of the plant, was compared after a growing period of 30 days after seeding, between the GGBS based substrates and rockwool which is considered as the market benchmark. As it can be observed in the table 19 below, plant growth was similar even exceeding rockwool.

(44) TABLE-US-00019 TABLE 19 Fresh and dry mass of the radishes GGBS Rockwool Substrate Benchmark Fresh mass 1.56 1.85 (g/plant) Dry mass 0.153 0.128 (g/plant)