The matl. comprises the granulate formed by the ash obtd. by burning coal dust in power stations, which consists of two fractions (a) the crude material; (b) granulate crushed to break down most of the extremely brittle material and, if necessary, using a limiting sieve size of 3 mm. Instead of using gravel for road building, a mixt. contg. 42% (a), 36% (b) and 12% fly-ash is used. The pref. size for (b) is 0-3 mm and the mixt. pref. also contains 5% cement and 5% water. The pref. use for the material is as a frost-protection layer in road construction. Provides better utilisation of a waste material available in large quantities without expensive grinding operations and only requiring a small amt. of cement.
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