Binder composition

1. A hydraulic binder composition in the form of a dry powder comprising:

(a) 10% to 95% MgO; and

(b) 5% to 80% magnesium carbonate;

(c) up to 10% chloride

based on the total weight of components (a) to (c)

wherein the magnesium carbonate is in the form xMgCO 3 .yMg(OH) 2 .zH 2 O

wherein x is a number that is at least 1, and at least one of y or z is a number that is greater than 0.

2. A hydraulic binder composition as claimed in claim 1 ,

wherein in the formula xMgCO 3 .yMg(OH) 2 .zH 2 O,

x is a number in the range of 3.5-4.5,

y is a number in the range of 0.5-1.5, and

z is a number in the range of 3.5-5.5.

3. A hydraulic binder composition as claimed in claim 1 ,

wherein in the formula xMgCO 3 .yMg(OH) 2 .zH 2 O,

x is 4,

y is 1, and

z is 4 or 5.

4. A hydraulic binder composition as claimed in claim 1 ,

wherein the magnesium carbonate is in the form xMgCO 3 .zH 2 O

wherein x is at least 1, and

z is greater than 0.

5. A hydraulic binder composition as claimed in claim 1 ,

wherein in the formula xMgCO 3 .yMg(OH) 2 .zH 2 O:

x, y, z are all greater than 0.

6. A hydraulic binder composition as claimed in claim 1 , wherein the magnesium carbonate is hydromagnesite.

7. A hydraulic binder composition as claimed in claim 1 , wherein the chloride is NaCl.

8. A binder composition as claimed in claim 1 , comprising MgO and/or Mg(OH) 2 , magnesium carbonate and optionally chloride in an amount selected from one of the following ranges:

i)

(a) 70% to 95% magnesium oxide (MgO);

(b) 5% to 20% of one or more magnesium carbonate; and

(c) up to 10% chloride

based on the total weight of components (a) to (c);

ii)

(a) 30% to 80% magnesium oxide (MgO);

(b) 20% to 60% of one or more magnesium carbonate; and

(c) up to 10% chloride

based on the total weight of components (a) to (c);

iii)

(a) 10% to 40% magnesium oxide (MgO);

(b) 60% to 80% of one or more magnesium carbonate; and

(c) up to 10% chloride

based on the total weight of components (a) to (c);

iv)

(a) 40% to 85% magnesium oxide (MgO);

(b) 5% to 30% magnesium hydroxide (Mg(OH) 2 );

(c) 10% to 20% of one or more magnesium carbonate;

(d) up to 10% chloride

based on the total weight of components (a) to (d);

v)

(a) 20% to 75% magnesium oxide (MgO);

(b) 5% to 30% magnesium hydroxide (Mg(OH) 2 );

(c) 20% to 40% of one or more magnesium carbonate; and

(d) up to 10% chloride

based on the total weight of components (a) to (d);

vi)

(a) 10% to 60% magnesium oxide (MgO);

(b) 30% to 50% magnesium hydroxide (Mg(OH) 2 );

(c) 10% to 30% of one or more magnesium carbonate; and

(d) up to 10% chloride

based on the total weight of components (a) to (d).

9. A hydraulic binder composition as claimed in claim 2 , comprising MgO and/or Mg(OH) 2 , magnesium carbonate and optionally chloride in an amount selected from one of the following ranges:

i)

(a) 70% to 95% magnesium oxide (MgO);

(b) 5% to 20% of one or more magnesium carbonate; and

(c) up to 10% chloride

based on the total weight of components (a) to (c);

ii)

(a) 30% to 80% magnesium oxide (MgO);

(b) 20% to 60% of one or more magnesium carbonate; and

(c) up to 10% chloride

based on the total weight of components (a) to (c);

iii)

(a) 10% to 40% magnesium oxide (MgO);

(b) 60% to 80% of one or more magnesium carbonate; and

(c) up to 10% chloride

based on the total weight of components (a) to (c);

iv)

(a) 40% to 85% magnesium oxide (MgO);

(b) 5% to 30% magnesium hydroxide (Mg(OH) 2 );

(c) 10% to 20% of one or more magnesium carbonate;

(d) up to 10% chloride

based on the total weight of components (a) to (d);

v)

(a) 20% to 75% magnesium oxide (MgO);

(b) 5% to 30% magnesium hydroxide (Mg(OH) 2 );

(c) 20% to 40% of one or more magnesium carbonate; and

(d) up to 10% chloride

based on the total weight of components (a) to (d);

vi)

(a) 10% to 60% magnesium oxide (MgO);

(b) 30% to 50% magnesium hydroxide (Mg(OH) 2 );

(c) 10% to 30% of one or more magnesium carbonate; and

(d) up to 10% chloride

based on the total weight of components (a) to (d).

10. A hydraulic binder composition as claimed in claim 4 , comprising MgO and/or Mg(OH) 2 , magnesium carbonate and optionally chloride in an amount selected from one of the following ranges:

i)

(a) 70% to 95% magnesium oxide (MgO);

(b) 5% to 20% of one or more magnesium carbonate; and

(c) up to 10% chloride

based on the total weight of components (a) to (c);

ii)

(a) 30% to 80% magnesium oxide (MgO);

(b) 20% to 60% of one or more magnesium carbonate; and

(c) up to 10% chloride

based on the total weight of components (a) to (c);

iii)

(a) 10% to 40% magnesium oxide (MgO);

(b) 60% to 80% of one or more magnesium carbonate; and

(c) up to 10% chloride

based on the total weight of components (a) to (c);

iv)

(a) 40% to 85% magnesium oxide (MgO);

(b) 5% to 30% magnesium hydroxide (Mg(OH) 2 );

(c) 10% to 20% of one or more magnesium carbonate;

(d) up to 10% chloride

based on the total weight of components (a) to (d);

v)

(a) 20% to 75% magnesium oxide (MgO);

(b) 5% to 30% magnesium hydroxide (Mg(OH) 2 );

(c) 20% to 40% of one or more magnesium carbonate; and

(d) up to 10% chloride

based on the total weight of components (a) to (d);

vi)

(a) 10% to 60% magnesium oxide (MgO);

(b) 30% to 50% magnesium hydroxide (Mg(OH) 2 );

(c) 10% to 30% of one or more magnesium carbonate; and

(d) up to 10% chloride

based on the total weight of components (a) to (d).

11. A hydraulic binder composition as claimed in claim 1 , wherein the average particle diameter of the MgO/Mg(OH) 2 particles is about 0.01 to 800 μm; and/or

wherein the average particle diameter of the magnesium carbonate particles is approximately 0.01 to 800 μm.

12. A hydraulic binder composition as claimed in claim 1 in a composition also comprising a filler.

13. The hydraulic binder composition of claim 1 wherein the composition is used for concrete, mortar or cement.

14. A construction product comprising the hydraulic binder composition claimed in claim 1 wherein the construction product is a block, a tile, a roof tile, a brick, or mortar.

15. A method of making a construction product comprising mixing together the hydraulic binder composition of claim 1 with:

(e) water and

(f) optionally an additive or filler and allowing the mixture to set.

16. The method of making a construction product according to claim 15 wherein the amounts of components (e) to (f) are, in weight % based on the total weight of components (a) to (f):

(e) 5-80%; and

(f) up to 99.

17. A kit for forming a hydraulic binder composition in the form of a dry powder comprising

(a) 10-95% magnesium oxide,

(b) 5-80% magnesium carbonate of the general formula I as defined in claim 1 and

(c) up to 10% chloride.