REQUIREMENTS FOR PAVING BRICK.
The rigidity of the requirements to be inserted in specifications or to be taken as standard in selecting paving brick for .a street will depend upon the conditions under which the brick are to be used. The amount of traffic and the methods and details of construction used in the con struction of the pavement, including such matters as the kind of filler used and the character of the foundation, will naturally have a bearing upon the requirements. A brick may be used on a street where there will be little traffic if it has sufficient weather-resisting qualities when it should be rejected for use with heavy traffic. A large amount of light traffic produces less wear than a much smaller amount of heavy traffic. In a pavement made with a high-grade cement filler the nricl: will be protected and the effect of spalling and impact may be much less than in a pavement with a sand filler. In a similar way the character of the foundation has to do with the grade of the brick to be chosen. For the purposes of this article it will be sufficient to divide traffic into four classes: (1) Very heavy traffic; (2) Heavy traffic; (3) Medium traf fic; and (4) Light traffic. Very heavy traffic would be such as would occur in the business district of our large cities and in certain districts of smaller cities. Heavy traffic would include that found in the busi ness districts of smaller cities. Medium traffic would be such as is found on the streets used as main thoroughfares in the smaller cities. Light traffic is such as is found in the remotest residence portions of the small cities, or streets not frequented. For very heavy traffic it is evi (lent that only the very best brick should he used and that a heavy foundation and a high-grade filler to protect the brick sll )uld be used. For the other classes of traffic the requirements may be le:a rigid except that a high degree of uniformity in the brick should be maintained.
The following limiting values for the requirements for brick for the several classes of traffic are suggested. They are given for the usual block size of brick. The maximum loss by the N. B. M. A. standard rattler test : (1) Very heavy traffic, 15 per cent; (2) Heavy traffic, 17 per cent; (3) Medium traffic, 21 per cent; (4) Light traffic, 24 per cent. For the brick size, 3 or 4 per cent may be added to the above limits, ex cept that the brick size would not be used for very heavy traffic. No values are suggested for the Talbot-Jones rattler since the standardiza tion of this machine is not yet complete. For the cross-breaking test the limits for the modulus of rupture may be made as follows: (1) Very heavy traffic, 3,000 pounds per square inch; (2) Heavy traffic, 2,500 pounds per square inch; (3) Medium traffic, 2,000 pounds per square inch; (4) Light traffic, 1,500 pounds per square inch. It should be noted that these values are subject to modifications, according to re quirements of traffic and conditions of the 'brick, and are not to be taken as iron-clad limits.. They are intended to apply to average samples of brick taken from piles along the street. The requirements for uniform ity and the methods of determining this uniformity from a separate con sideration. The limiting variation from the specified value for the modulus of rupture may be made a requirement. It is frequently pos sible to select from the piles of brick of varying degrees of quality and make tests of these. In case that one of these grades representing a cer tain percentage of the brick on a portion of the street, say, 5 or 10 per cent, falls below the requirements, they should be rejected. The matter of the selecting of these samples will be discussed under "Inspection."