Joints and cracks can be successfully treated by thoroughly cleaning them and filling when dry, and preferably during warm weather, with hot tar, then covering with dry sand or screenings. The tar should be permitted to lap over the spalled edges of the crack, but not to exceed 1 inch. The most desirable covering is clean, coarse sand or cleans creenings of stone, slag or gravel, that will pass a 4-inch circular opening, and be retained on a-inch mesh screen. The tar should be poured when hot enough to run readily into the crevices of the pavement (about 200° to 250° F.). It is believed that no large excess of the tar should be used as the frequent use of such an excess might eventually build up an elevation on the surface which would be objectionable to traffic. The covering of screenings or sand should be put on immediately after pouring the tar so that while in the liquid state it will unite with the screenings or sand in sufficient degree to prevent the tar from sticking to wheels of vehicles or melting during hot periods and running from the cracks. The use of a mastic consisting of a mixture of hot tar and sand, in place of pure tar, for filling the cracks and joints, gives promise of excellent results; but perhaps it is too soon to give definite specifications for this mixture. The filling of the larger and more open cracks or joints with the mastic, and the use of the pure tar for filling the minor openings in the pavement and such as are made necessary by settlement after the joints have been originally filled with the mastic, may be found to be most satisfactory. A pouring can with a round or vertical spout is very satisfactory for pouring tar in filling cracks and joints. Inasmuch as it is desired that the tar shall lap over the edges of the crack or joint, the use of a conical pouring can would be of doubtful economy. Small holes and shallow depressions can be successfully treated as follows: Clean surface thoroughly. Where the surface is disintegrated it should first be thoroughly swept with a steel broom in order to remove all loose spalls or foreign matter; afterward, the dust must be removed by sweeping with a rattan or house broom. The hot tar is then applied to the dry concrete and rubbed well with a squeegee or stiff broom to secure a good bond to the surface of the concrete. The tar is then covered with coarse sand or screenings (to inch) of stone, slag or gravel. The amount of tar used will vary from to 1 gallon per square yard, depending upon the depth of the depression to be filled. When more than gallon per square yard is used, it should be applied in two coats and the excess screenings swept off before the second coat is applied. The more tar that is applied to the surface, the more desirable it is to have the coarser material for a covering. In filling small holes the application of the tar in two layers would, of course be unnecessary. To repair larger holes and deeper depressions than those discussed above: Thoroughly clean and paint the surface with tar. Fill the hole or depression with broken stone, preferably of such size that they will not exceed in diameter one-half the depth of the depression to be filled nor exceed in size stone suitable for an ordinary tar macadam. The stone should be levelled off and compacted as well as may be by tamping or rolling so as to conform to the true surface of the road. The voids are then filled with the hot tar and screenings applied to the surface, which is again compacted and treated as in building a tar macadam. The use of a cold mix consisting of clean, hard stone chips coated with a coal tar cutback, for filling such holes and depressions, as described under the above paragraph, has been followed to some extent with very promising results. The stone chips are first thoroughly coated with the cold tar preparation by turning with shovels after the tar has been sprayed upon them, as in mixing ordinary cement concrete. The mixture is then permitted to stand a few days until the lighter oils vaporize from the tar, which leaves the stone coated with the heavy tar. The coated chips are then well tamped into the hole or depression to be filled, the shallower depressions being first painted with the pure tar. Coarse sand or fine screenings are then spread over the surface. If the voids appear quite open after the coated chips have been thoroughly tamped, a light application of the tar is made to seal up the voids before the surface screenings are applied. Where the pavement is disintegrated badly or broken clear through so as to require rebuilding, it should be cut away with vertical edges. After the subgrade is levelled and compacted and the edges and subgrade thoroughly dampened (but the foundation not made muddy), the part cut away is replaced with new concrete conforming in quality as nearly as possible to the concrete of the surrounding pavement. It is well to coat the edges of the old concrete with cement grout. Care should be taken that the surface of the new concrete conforms to the surface of the adjacent concrete. The new concrete should be kept well dampened for about seven days, and protected from traffic (ten days in warm weather and much longer in cold weather) until thoroughly hardened. If the replacement is over an excavation the concrete should be properly reinforced. STANDARD SPECIFICATIONS FOR PORT LAND CEMENT1 1. Portland cement is the product obtained by finely pulverizing clinker produced by calcining to incipient fusion, an intimate and properly proportioned mixture of argillaceous and calcareous materials, with no additions subsequent to calcination excepting water and calcined or uncalcined gypsum. 2. Chemical Properties.-The following limits shall not be exceeded: Loss on ignition, per cent. 4.00 0.85 2.00 5.00 3. Physical Tests.-The specific gravity of cement shall be not less than 3.10 (3.07 for white Portland cement). Should the test of cement as received fall below this requirement a second test may be made upon an ignited sample. The specific gravity test will not be made unless specifically ordered. 4. The residue on a standard No. 200 sieve shall not exceed 22 per cent by weight. 5. A pat of neat cement shall remain firm and hard, and show no signs of distortion, cracking, checking, or disintegration in the steam test for soundness. 6. The cement shall not develop initial set in less than fortyfive minutes when the Vicat needle is used or sixty minutes when the Gillmore needle is used. Final set shall be attained within ten hours. 7. The average tensile strength in pounds per square inch of not less than three standard mortar briquettes composed of one part cement and three parts standard sand, by weight, shall be equal to or higher than the following: 1 Adopted by the American Society for Testing Materials in 1904 and revised in 1908, 1909 and 1916. These specifications are the result of several years' work of a special committee representing a United States Government Departmental Committee, the Board of Direction of the American Society of Civil Engineers and Committee C-1 on Cement of the American Society for Testing Materials, in cooperation with Committee C-1. The specifications as here printed are but the first part of the Society's "Standard Specifications and Tests for Portland Cement," as officially published. 8. The average tensile strength of standard mortar at twentyeight days shall be higher than the strength at seven days. 9. Packages, Marking and Storage.-The cement shall be delivered in suitable bags or barrels with the brand and name of the manufacturer plainly marked thereon, unless shipped in bulk. A bag shall contain 94 pounds net. A barrel shall contain 376 pounds net. 10. The cement shall be stored in such a manner as to permit easy access for proper inspection and identification of each shipment, and in a suitable weather-tight building which will protect the cement from dampness. 11. Inspection. Every facility shall be provided the purchaser for careful sampling and inspection at either the mill or at the site of the work, as may be specified by the purchaser. At least ten days from the time of sampling shall be allowed for the completion of the 7-day test, and at least 31 days shall be allowed for the completion of the 28-day test. The cement shall be tested in accordance with the methods hereinafter prescribed. The 28-day test shall be waived only when specifically ordered. 12. Rejection. The cement may be rejected if it fails to meet any of the requirements of these specifications. 13. Cement shall not be rejected on account of failure to meet the fineness requirement if upon retest after drying at 100°C. for one hour it meets this requirement. 14. Cement failing to meet the test for soundness in steam may be accepted if it passes a retest using a new sample at any time within 28 days thereafter. 15. Packages varying more than 5 per cent from the specified weight may be rejected; and if the average weight of packages in any shipment, as shown by weighing 50 packages taken at random, is less than that specified, the entire shipment may be rejected. PETROLEUM AND RESIDUUMS1 A large part of the materials used as dust preventives and binders to hold together the mineral constituents of roads are obtained from petroleum. Petroleum is a term which covers mineral oils of a great variety of characteristics, all alike in being composed of a great variety of complex chemical compounds called hydrocarbons, of which there is a very large number. The investigation of the properties of these hydrocarbons and their derivatives requires a knowledge of organic chemistry which few roadbuilders possess, and because some of them have attempted to tread the veritable mazes of this extremely complicated domain of chemistry, no little confusion has arisen. The main facts regarding petroleum and the other hydrocarbons used in roadbuilding are definitely known, but the details of any group of these compounds are best left for the chemical specialist, who is making steady progress in his researches concerning them. Paraffin and Asphaltic Oils The roadbuilder's interest in petroleum is largely in its base, a term used to designate a part of oil left after distilling off the more volatile portions. The base is sometimes made up of compounds of the paraffin group or series, as chemists term such allied compounds. Marsh gas is a member of the paraffin series, and its least complex representative. A few other members are gases but most of them are liquids or solids, and their number is legion. The base of other petroleums is made up of compounds called polycyclic polymethylenes by the chemist, and as these compounds occur in native asphalts such a base is called asphaltic. The base of other petroleums is made up of both paraffin and asphaltic compounds and such petroleums are called semiasphaltic. The gaseous hydrocarbons are of no interest to the roadbuilder. The liquid and solid hydrocarbons are what determine the value of petroleum for his purposes. The liquid and solid paraffins are greasy materials without binding properties, while the asphaltic materials are sticky. Consequently the roadbuilding value of petroleum depends upon the asphaltic compounds in its base. 1 Revised by Prévost Hubbard, chief of road materials tests and research, United States Office of Public Roads. |