CLAIMS 1. A joint filling mixture for pavements and the like consisting essentially of sand; and at least one sodium containing substance being able to provide sustained release of sodium to an aqueous phase in contact with the sodium containing substance and maintain a herbicidally effective concentration of sodium in the aqueous phase filling the pores of the joint filling sand when wetted by rain water. 2. A joint filling mixture according to claim 1, where the herbicidally effective concentration of sodium in the aqueous phase is stated as the molar concentration of sodium ions, [Na+], where [Na+] is 10'3 or more, such as where [Na4] is lfC1 or more, where [Na+] is 10'5 or more, where [Na+] is 10-6 or more. 3. A joint filling mixture according to claim 1 and 2, where the molar concentration of calcium ions [Ca4^] is 2.5E-02 or less 4. A joint filling mixture according to any of the above claims, where the joint filling mixture is capable of resulting in an initial SAR value in the aqueous phase of 10 or more, such as 12 or more, such as 14 or more. 5. A joint filling mixture according to claim 1, where the joint filling mixture has an ESP value of 12% or more, such as 15% or more, such as 18% or more. 6. A joint filling mixture according to any of the above claims, where the mass relationship, stated as mass(sodium containing substance(s)) / mass(sand) is between 0.5/99.5 and 10/90, such as between 1/99 and 5/95 7. A joint filling mixture according to any of the preceding claims, where the joint filling mixture is capable of resulting in a pH value in the aqueous phase of 9 or more, such as 10 or more, such as 11 or more, such as 12 or more 8. A joint filling according to any of the preceding claims, where sodium release is sustained for more than 2 years, more specifically 5 years more specifically 10 years 9. A joint filling mixture according to any of the above claims, where the sodium containing substance comprises one or more substances selected from the group consisting of -sodium containing silicates, such as one or more sodic feldspatoids, such as the sodic feldspatoids selected from the group consisting of sodalites, analcimes, sodic nepheline, andCLAIMS 1. A joint filling mixture for pavements and the like consisting essentially of sand; and at least one sodium containing substance being able to provide sustained release of sodium to an aqueous phase in contact with the sodium containing substance and maintain a herbicidally effective concentration of sodium in the aqueous phase filling the pores of the joint filling sand when wetted by rain water. A joint filling mixture according to claim 1, where the herbicidally effective concentration of sodium in the aqueous phase is stated as the molar concentration of sodium ions, [Na +], where [Na +] is 10'3 or more, such as where [Na4] is lfC1 or more, where [Na +] is 10'5 or more, where [Na +] is 10-6 or more. 3. A joint filling mixture according to claim 1 and 2, where the molar concentration of calcium ions [Ca4 ^] is 2.5E-02 or less 4. A joint filling mixture according to any of the above claims, where the joint filling mixture is capable of resulting in an initial SAR value in the aqueous phase of 10 or more, such as 12 or more, such as 14 or more. A joint filling mixture according to claim 1, where the joint filling mixture has an ESP value of 12% or more, such as 15% or more, such as 18% or more. A joint filling mixture according to any of the above claims, where the mass relationship, stated as mass (sodium containing substance (s)) / mass (sand) is between 0.5 / 99.5 and 10/90, such as between 1 / 99 and 5/95 7. A joint filling mixture according to any of the preceding claims, where the joint filling mixture is capable of resulting in a pH value in the aqueous phase of 9 or more, such as 10 or more, such as 11 or more, such as 12 or more 8. A joint filling according to any of the preceding claims, where sodium release is sustained for more than 2 years, more specifically 5 years more specifically 10 years 9. A joint filling mixture according to any of the above claims, where the sodium containing substance comprises one or more substances selected from the group consisting of -sodium containing silicates, such as one or more sodic feldspatoids, such as the sodic feldspatoids selected from the group consisting of sodalites, analcimes, sodic nepheline , and
Other industrially derived glasses or wastes essentially having a chemical composition as the natural minerals or calcium silicate glass 10. A joint filling mixture according to preceding claim, where the sodium containing substance is sodalite and the mass relationship, stated as mass(sodalites) / mass(sand) is between 0.5/99.5 and 10/90, such as between 1/99 and 5/95. 11. A joint filling mixture according to any of the above claims, where the sodium containing substance comprises one or more substances selected from the group consisting of sodium silicate glasses 12. A joint filling mixture according to preceding claims, where the sodium containing substance is sodium silicate glass and the mass relationship, stated as mass(sodium silicate glass) / mass{sand) is between 0.5/99.5 and 10/90, such as between 1/99 and 5/95. 13. A joint filling mixture according to any of the above claims, where the sodium containing substance comprises one or more cat-ionic exchange materials selected from the group consisting of zeolites, clays, organic materials comprising humic acid, ion-exchange polymeric materials, high surface area carbonaceous materials, which cat-ionic exchange materials comprises exchange sites with Na+ 14. A joint filling mixture according to any of the above claims, where the sand is a mixture of a quartz sand and one or more non-quartz sand(s) and where the mass relationship stated as mass(quartz sand) / mass(sand), is 70/30 or more, such as 90/10 or more, such as 95/5 or more, such as 99/1 or more, such as 99.9/1 or more. 15. A joint filling mixture according to any of the above claims, where the mean particle size of the sand is between 0.05 mm and 5 mm, such as between 0,05 mm and 3 mm, between 0.05 mm and 2 mm, between 0.05 mm and 1 mm 16. Use of a joint filling mixture according to any of claims 1-15 for weed control.Other industrially derived glasses or wastes essentially having a chemical composition as the natural minerals or calcium silicate glass 10. A joint filling mixture according to previous claim, where the sodium containing substance is sodalite and the mass relationship, stated as mass (sodalites) / mass (sand) is between 0.5 / 99.5 and 10/90, such as between 1/99 and 5/95. 11. A joint filling mixture according to any of the above claims, where the sodium containing substance comprises one or more substances selected from the group consisting of sodium silicate glasses 12. A joint filling mixture according to previous claims, where the sodium containing substance is sodium silicate glass and the mass ratio, stated as mass (sodium silicate glass) / mass {sand) is between 0.5 / 99.5 and 10/90, such as between 1/99 and 5/95. 13. A joint filling mixture according to any of the above claims, where the sodium containing substance comprises one or more cat-ionic exchange materials selected from the group consisting of zeolites, clays, organic materials comprising humic acid, ion-exchange polymeric materials, high surface area carbonaceous materials, which cat-ionic exchange materials comprises exchange sites with Na + 14. A joint filling mixture according to any of the above claims, where the sand is a mixture of a quartz sand and one or more non-quartz sand ( s) and where the mass relationship stated as mass (quartz sand) / mass (sand), is 70/30 or more, such as 90/10 or more, such as 95/5 or more, such as 99/1 or more , such as 99.9 / 1 or more. 15. A joint filling mixture according to any of the above claims, where the mean particle size of the sand is between 0.05 mm and 5 mm, such as between 0.05 mm and 3 mm, between 0.05 mm and 2 mm, between 0.05 mm and 1 mm 16. Use of a joint filling mixture according to any of claims 1-15 for weed control.