Process for preparing a filler for asphalt or concrete starting from a slag material

1. A process for preparing, starting from a slag material, a filler for use in construction materials which contain a hydraulic or bituminous binding agent, characterised in that use is made of a slag material containing γ-dicalcium silicate; and in that the process comprises the steps of:

removing a finer fraction from the slag material to divide the slag material in said finer fraction and in a coarser fraction, wherein the coarser fraction comprises crystalline phases and has a γ-dicalcium silicate content which is less than 4% by weight of said crystalline phases, wherein the coarser fraction comprises particles having a particle size greater than 0.75 mm, and wherein the finer fraction comprises particles having a particle size that is smaller than the particle size of the particles of the coarser fraction; and

finely milling at least a portion of said coarser fraction of the slag material to obtain a filler, from only the coarser fraction, of which at least 50% by weight is formed by particles not bigger than 63 μm.

2. A process according to claim 1 , characterised in that said slag material comprises a steel slag.

3. A process according to claim 1 , characterised in that it additionally comprises the step of breaking the slag material into fragments smaller than a size x before removing said finer fraction from the slag material, wherein said size x is at most 50 mm, but larger than 2.0 mm.

4. A process according to claim 3 , characterised in that it further comprises the step of removing metal from the slag fragments.

5. A process according to claim 4 , characterised in that after having removed said metal and said finer fraction from the slag material, the coarser fraction of the slag material is divided in at least a first portion and in a second portion which has a lower metal content than the first portion, said portion of the coarser fraction of the slag material which is finely milled to obtain the filler being said first portion of the slag material.

6. A process according to claim 1 , characterised in that said finer fraction is removed from the slag material by sieving the finer fraction out of the slag material and/or by washing it out of the slag material.

7. A process according to claim 1 , characterised in that it further comprises the step of removing metal from said portion of the coarser slag material fraction after said fine milling step.

8. A process according to claim 7 , characterised in that said metal is removed out of the finely milled portion of the coarser slag material fraction by a dry separation process.

9. A process according to claim 1 , characterised in that the fine milling step is carried out by dry milling.

10. A process according to claim 1 , characterised in that said filler is less than 50% amorphous by weight.

11. A process according to claim 1 , characterised in that said portion of the coarser slag material fraction is finely milled so that said filler has a Blaine value of at least 2000 cm 2 /g.

12. A process according to claim 1 , characterised in that said portion of the coarser slag material fraction is finely milled so that at least 60% by weight of the filler is formed by particles not bigger than 125 μm.

13. A process according to claim 1 , wherein the coarser fraction comprises particles having a particle size greater than about 1.0 mm.

14. A process according to claim 1 , wherein the coarser fraction comprises particles having a particle size greater than about 1.5 mm.

15. A process according to claim 1 , wherein the coarser fraction comprises particles having a particle size greater than about 2.0 mm.

16. A process according to claim 1 , characterised in that at least 60% by weight of said filler is formed by particles not bigger than 63 μm.

17. A process according to claim 1 , characterised in that said filler is less than 30% amorphous by weight.

18. A process according to claim 1 , characterised in that said portion of the coarser slag material fraction is finely milled so that said filler has a Blaine value of at least 3000 cm 2 /g.

19. A process according to claim 1 , characterised in that said portion of the coarser slag material fraction is finely milled so that at least 80% by weight of the filler is formed by particles not bigger than 125 μm.

20. A process according to claim 1 , characterised in that the γ-dicalcium silicate content of said coarser fraction is less than 3% by weight of said crystalline phases thereof.

21. A process according to claim 1 , characterised in that the γ-dicalcium silicate content of said coarser fraction is less than 2% by weight of said crystalline phases thereof.

22. A process according to claim 2 , characterised in that said steel slag is a stainless steel slag.

23. A process according to claim 3 , characterised in that said size x is at most 30 mm.

24. A process according to claim 3 , characterised in that said size x is at most 20 mm.

25. A process according to claim 3 , characterised in that said size x is larger than 4 mm.

26. A process according to claim 3 , characterised in that said size x is larger than 8 mm.

27. A process according to claim 3 , characterised in that said size x is larger than 10 mm.