1,146,160. Treating slags. MANNESMANN A.G. 12 Aug., 1966 [18 Oct., 1965], No. 36099/66. Heading C1K. Particulate road building material is obtained by mixing, as liquids, blast furnace slag with Siemens-Martin or L.D. converter slag, cooling in a casting bed, and crushing the solid product, the ratio of blast-furnace to the other slag being such that the free lime of the other slag is bound as silicate and/or aluminate, and the mixed slags have a total iron content giving low porosity in the solid. The allowable iron content varies inversely to the alkali metal content of the blast furnace slag, and the maximum amount of steel making slag corresponds to a total iron content of 10%.