307,751. Lefebvre, C. G. J., and Berger, E. E. F, March 12, 1928, [Convention date]. Bituminous compositions. - A tarry binder .adapted to be applied to roads as a dressing or mixed with stones to form tar macadam has incorporated with it a mineral filler, consisting of an impalpable stone powder passing a 300 screen, the filler amounting to at least 60 per cent by weight of the tar mixture. Non-porous natural or artificial stone is used as the filler, for example crushed or ground quartz sand, quartzites, porphyries, diorites, hard or marmorean limestones, clinkers, &c. Porous or conchiferous limestones, lime, chalks, slags, slates, and clays are not suitable. In an example 80 per cent of filler is added to a binder consisting of 100 parts of tar, 40 parts of coal pitch and 10 parts of petroleum bitumen. Larger grained sand may also be added to the binder. Specification 216,911 is referred to.
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