THE BRICK.
Character—A paving brick is simply a brick which, owing to careful selection of the clay and to skill in the manufacture, is so hard and tough that it will resist the crushing and the abrading action of the traffic. The brick should be reasonably perfect in shape, should be free from marked warping or distortion, and should also be uniform in size, so as to fit closely together and make a smooth pavement. Any par ticular brick should be homogeneous in texture and should be free from lamination or seams, so as to wear uniformly; and all the brick used in a pavement should be of the same grade so that the pavement may wear evenly.
Testing—To determine the difference in quality of bricks of different manufacture, it is necessary to carefully test them. This is done by rolling the bricks or blocks with blocks of cast-iron in a revolving cast iron cylinder or "rattler." The National Brick Manufacturer's Asso ciation, as a result of an extended series of experiments, has adopted a standard method of conducting this test which is so well known or so easily obtained as to make it unwise to give the details here.
Different bricks are rated according to the loss by wear in the "rattler ;" but the per cent of loss will depend upon the care employed in culling the brick and in selecting the samples, as well as upon the character of the brick. To show the results that may be expected, the following data obtained by a city in Illinois in the ordinary course of business are given. The samples were selected after delivery upon the the street, by a representative of the city. The tests were carefully made according to the "N. B. M. A. standard" as above. The material was in the form of books approximately 3" x " 9". The average loss of ten lots was 18.34 per cent with a range from 15.4 to 24.6 per cent;
and omitting the largest result, the average was 17.64 per cent with a range from 15.4 to 21.2 per cent. Of the ten kinds of blocks, two had losses of less than 16 per cent, four less than 18, six less than 19, and eight less than 20 per cent.
The above data are for blocks approximately 3" x 4" x 9". Bricks approximately 2" x 4" x 8" will lose from 2 to 6 per cent more than the above blocks; but not enough data have been accumulated to deter mine with any accuracy the effect of size upon the loss in the rattler test.
A study of the details of the experiments referred to above indicates that an occasional manufacturer can furnish paving blocks giving a loss of 15 per cent or even less; but whether it is wise so to specify will de pend upon the service required and upon the cost of different grades of paving blocks. A severe specification will require more careful culling of the product of the kiln and will also limit competition—both of which demands will increase the cost. The limit to be specified in any particular case will depend upon the special conditions'; and should be the result of very careful study of the attendant conditions.
Setting the Brick—There is neither space nor need of discussing this subject here, further than to say that each brick should be pressed or rather struck against the side and also the end of the bricks already in position.
Inspection—After the bricks have been set in position the pavement should be carefully inspected, and all very soft or very hard bricks should be removed so that the pavement may wear uniformly. A brick having only a small piece chipped from the corner or edge may be turned over.