Because of the prominence that natural, sandstone, rock asphalt enjoyed in Kentucky during the past 50 years, sand-asphalts and sheet-asphalt mixes have not been used very extensively for paving in Kentucky. This is somewhat unfortunate because the natural, sand stone, rock asphalt has not been available since about 1955 and because there is now a need for a fine-textured, skid-resistance, wearing course for resurfacing work as well as on new pavements. These circumstances, coupled with the realization (1953-54) that surface courses and chip seals using 100% limestone aggregates tend to become slick, have emphasized the need for specifications for sand-asphalts. Further, it was in the interest of "building in" skid-resistance (about 1954) that Class I, Type B, surface was required to contain 50% siliceous, river sand for work on all roads having more than 700 vpd. Class I, Type B surface is normally laid 1-1/4 inches in depth -- which would be equivalent to about 65 lbs. of river sand per sq. yd. This sometimes requires that river sands be transported into areas where manufactured limestone sands might otherwise be more economically available. Whereas the river sands are sought for the skid-resistance which they impart to the surface, river sands are notably deficient in fine sizes (filler) which impart stability and integrity to the mix.

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No. 166

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