115

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Sand and screenings passing the 10-mesh sieve shall conform to the following proportions by weight:— Passing 200-mesh sieve—between 4 and 10 per cent. Passing 80-mesh sieve—between 25 and 50 per cent. Passing 40-mesh sieve—between 60 and 80 per cent. Passing 10-mesh sieve—loo per cent. Sand passing the 10-mesh sieve shall conform to tho following proportions by weight:— Passing 200-mesh sieve—between 2 and 6 per cent. Passing 80-mesh sieve—between 24 and 48 per cent. Passing 40-mesh sieve—between 60 and 80 per cent. Passing 10-mesh sieve—loo per cent. The exact proportions, within the above limits, shall be regulated to produce a dense mixture with minimum voids and with the voids filled with bituminous material. Asphaltic Cement. —Asphaltic cement used under these specifications must be prepared from the products of California crude asphlatic petroleum. It shall be an oil asphalt of the required degree of penetration, or a mixture of a refined liquid asphalt with a refined solid oil asphalt, and must be free from admixture with any residues obtained by the artificial distillation of coal-tar or paraffin oil. Asphaltic cement shall be tested in accordance with the methods prescribed by the American Society for Testing Materials, except as to the test for solubility in carbon tetrachloride, which shall be made in accordance with the methods of the California Highway Commission hereinafter prescribed, and shall conform to the following requirements : — (a.) Asphaltic cement jghall be homogeneous and free from water. (b.) Penetration of original sample at 77° F. during five seconds with 100-gramme weight — 50° to 60°. (c.) Penetration of same sample at 77° F. during five seconds with 100-gramme weight after heating for five hours at 325° F.—not less than 60 per cent, of original penetration. (d.) Loss, after heating five hours at 325° F. —not more than 2 per cent. (c.) Total bitumen soluble in carbon disulphide —not less than 99-5 per cent. (f.) Per cent, of total bitumen soluble in carbon tetrachloride—9B per cent. (g.) Ductility at 77° ¥.— 3O to 40 centimetres. In the tost for solubility in cold carbon tetrachloride 200 cubic centimetres of the solvent shall be poured on 1 gramme of the asphaltic cement, and the mixture allowed to stand for eighteen hours at a temperature of 77° F. and then filtered at 77° F. During the test the mixture shall be subjected to nonactinic light only. All shipments of material shall be marked with a lot-number and penetration, and ten samples taken on random from each lot shall not vary more than 15 per cent, from the average penetration. Broken Stone. —The broken stone used for the asphaltic concrete shall be clean, hard, and tough stone of uniform quality, free from disintegrated material, and such that when tested with the PageDeval abrasion machine in the laboratory of the Commission it shall have an average coefficient of wear (French) of not less than 10. Said tests to be made in accordance with tho methods in use at the laboratory of the California Highway Commission. Sand. —The sand for the asphaltic concrete may be either a natural or a manufactured product, and shall be clean, hard-grained, and moderately sharp, and shall contain not more than 3 per cent. of loam, clay, organic matter, or other earthy impurities, nor, in the opinion of the engineer, mica in sufficient quantity or quality to be detrimental to the material. All impurities shall be determined in accordance with the methods in use at tho laboratory of the California Highway Commission. It shall be so graded as to produce in the finished surface mixture the mesh requirements elsewhere herein specified. It shall not contain more than 6 per cent, of material that will pass a No. 200 sieve. Screenings. —Screenings shall be the product of the crusher which will pass a J in. square screen, and shall be made from rock conforming in hardness to the requirements for broken stone hereinbefore specified. Screenings shall not contain more than 5 per cent, of mica, loam., clay, organic matter, or other earthy impurities. Stone-dust. —The stone-dust may be finely powdered limestone or Portland cement, and shall be of such fineness that all of it will pass a No. 50 sieve, and at least 66 per cent, shall pass a No. 200 sieve. Samples. —The contractor shall furnish to the engineer for test whenever called for, and free of charge, samples of all the materials entering into the composition of the pavement, the asphalt and asphaltic cement to be furnished in boxes ; and the said engineers shall have access at all times to all branches of the work. All tests shall be open to the contractor. Mixing. —The materials above described shall be heated, screened, and mixed by the following method : The broken stone and sand shall be roughly mixed and evenly fed to the driers, and shall be thoroughly dried to a temperature between 300° and 375° F. The temperature of the sand and stone shall not vary from each other more than 30°. Proper screens approved by the engineer shall be provided for separating the materials into various sizes. The screen sizes shall be 2f in., ljin., and Jin., either circular or square openings, as the contractor may elect, £ in. square mesh and 10-mesh. The openings of the 10-mesh screen shall conform to standard 10-mesh size. Screens shall be of such capacity or so arranged that the three larger-mesh screens will screen out at least 90 per cent, of the material coming to them, and the smaller screens at least 80 per cent, of the material coming to them.