To be efficient these joints should not be less than inch when spaced 5o feet apart. Such joints will usually be nearly closed in a few months, the paving pitch being forced out by the expansion. After com pletion, the pavement should stand at least a week or ten days before it is opened to traffic, to allow sufficient time for the cement to harden. During this time it should not be exposed to hot sun or per mitted to dry out too much; commonly a light coating of sand is spread over it, or sometimes it is dampened by frequent sprinklings.
Bituminous Filler. Bituminous cement is used as a filler for brick pavements. In some instances this consists of a coal-tar distillate; in others, of asphalt cement similar to that used in the surface of asphalt pavements; or a mixture of the two may be employed, a small amount of asphalt being added to the tar to make it less susceptible to changes of temperature.
On account of the variation in the materials used, the results obtained with bituminous fillers have differed widely in different places. The difficulty of classifying the materials employed, on account of the confusion in names used in designating them, makes it difficult to determine the relative values of the various mixtures which have been used for this purpose. In many cases very satisfactory results have been obtained with these fillers; in others, the susceptibility to tem perature changes has made them failures, the material melting and running out of the joints in hot weather, and becoming brittle and chipping out in cold weather.
The bituminous filler, when well constructed, makes a very satisfactory filler. It has the advantage over sand of being quite impervious to water, while it is not so rigid as the Portland-cement filler and does not give the rumbling sound to the pavement.
When bituminous filler is employed it is melted in kettles on fhe street and poured hot into the joints. The paving-cement is applied at a temperature of 250° to 300° F., and should be applied only when the bricks are dry. After the joints are filled a light layer of sand is spread over the surface, and serves under the traffic to clean the surface from any surplus tar which may be smeared over it.
Specifications for bituminous filler differ widely in character, in most cases providing no tests, but depend ing upon the manufacturer to provide a suitable material. The Chicago, 1907, specifications call for "a paving pitch which is the direct result of the dis tillation of straight run' coal tar and of such quality and consistency as shall be approved by the Board of Local Improvements." The Newark, N. J., specifica tions require a paving pitch " which shall be composed of twenty (20) parts of approved refined asphalt, and three parts of oil mixed with one hundred parts of pitch, both obtained from a direct distillation of coal tar, and ordinarily numbered four (4) at the manufactory. The proportions must be obtained by weight. The contractor must furnish the engineer with an affidavit from the manufacturer or refiner stating that the materials are the kind specified."
The specifications used by City Engineer E. A. Harper in Kansas City in 1907 require the testing of the filler in much the same manner that is employed for asphalt street surface. They are as follows: "Said asphalt filler shall remain ductile at all tem peratures. It shall be an absolute waterproofing. It shall firmly adhere to the brick and yet be pliable rather than rigid, thus providing for expansion and contraction and traffic conditions. This filler shall be heated to a temperature of 35o° F. or until it will run from a dipper without stringing. It shall 'then be put in a cylindrical pointed can and poured between the interstices of the brick until the filler is flush with the top of the brick. If necessary the interstices shall be gone over a second time.
"It shall be free from water or decomposition products.
"The various hydrocarbons composing it shall be present in homogeneous solution, no oily or granular character being present.
" It must, when tested at 77° F., have a penetration of from 3 to 9 millimeters when tested for five seconds with a No. 2 needle weighted with zoo grams, accord ing to the nature of the asphalt and the conditions under which it is employed. It must not be so sus ceptible to changes of temperature that if at 32° F. it shows a hardness indicated by I millimeter penetra tion, at 115° F. it will not be so soft as to give more than 35 millimeters penetration, using the above method of testing.
"Twenty grams of it shall not lose more than four per cent in weight upon being maintained at a uniform temperature of 325° F. for seven (7) hours in a cylindrical vessel two and one-half (2-i) inches in diameter by two (2) inches high.
"Twenty (20) grams of it shall not lose more than eight and one-half (8-i) per cent upon being maintained at a uniform temperature of 400° F. for seven (7) hours in a cylindrical vessel two and one-half (2/) inches in diameter by two (2) inches high.
" It shall be soluble in chemically pure carbon bi sulphide at air temperature to the extent of at least ninety-five (95) per cent.
" It shall not contain of carbonaceous matter insoluble in chemically pure carbon bisulphide, air temperature, more than four and one-half (4i) per cent.
" It shall be soluble in 87° Baume petroleum naphtha, air temperature, to the extent of not less than sixty-five (65) per cent and not more than eighty (8o) per cent.
" Its solubility in carbon tetrachloride shall not be re than one and one-half (q) per ,cent less than its sility in carbon bisulphide — both tests being made at air temperature.
" It shall show of fixed carbon not more than fifteen (15) per cent.
" It shall show a flashing point (New York State Closed Oil Tester) of more than 35o° F.
" It shall not contain more than five (5) per cent of parafin scale, the Holde method of determining parafin scale being used."