PAVING-BRICK CLAYS.
The problem to be solved in the production of street-paving brick is principally that of compounding clays, or of selecting clays with a special view to manufacturing tough vitrified brick.
In a large number of localities in the United States there are shale clays which are by nature specially adapted to the manu facture of vitrified brick for street-paving purposes. But all localities in which a market exists for such brick, and where it is desired to make the brick for roadway paving, are not so favored, and in such places the question of the proper selection and mixture of materials as will result in producing a hard, tough, street-paving brick is the all-important one.
It is not possible to make good brick for roadway paving from any and all kinds of brick earth. Dirt and clay mixed, and mixtures of sand and fire-clay, and fire-clay and ordinary building-brick clays will not make satisfactory paving-brick. Mr. J. H. Calkins, of Galesburg, Ill., in speaking of this subject, says : " The result of trying to make pavers out of poor clay will be a failure. To make good pavers you want to select a clay which, by giving it a hard burn, will melt together like iron, so that not a particle of water can soak into it, and which can not be even marred by a steel drill. When you have found such a clay, thoroughly pulverize it, make a stiff mixture with water, and mould your brick on a machine with an end pressure. Get all the clay into the brick that you possibly can do ; dry as other brick, only give them a harder burn." Mr. W. A. Eudaly, Cincinnati, Ohio, says : • " The idea of using a number one fire-clay for paving-brick is a mistake. What I mean by a number one fire-clay is such as Mount Savage clay, or what we in the West compare to a Mount Sav age clay. Such clays are of no use for paving-brick. They will not vitrify, and when burned have no strength ; will not stand the frost, but crumble and fall to pieces with the action of frost and wear. A low grade of fire-clay, however, will make an excellent paving-brick, for the reason that it will stand a high degree of heat in burning, and yet can be vitrified, and is usually strong and tough when well burned. Most low grades of fire-clay possess this quality of toughness, hence the idea that fire-clay must be used for paving-brick. You can often get paving-brick by mixing number one fire-clay with common clay, providing the latter will also stand a high degree of heat in burning. You run the risk, however, of making a brittle brick, as you are likely to burn the life out of the com mon clay before the fire-clay has been affected by the heat."
Mr. F. E. Frey, Willoughby, Ohio, in this connection says : " I have some experience in the mixing and manipulation of different clays for the manufacture of street-paving-brick. I have seen it done at Columbus, Ohio, where they have a shale clay like fire-clay. By itself it will not make a good brick, but by mixing it with sand and a kind of red clay having iron in it, it makes a good paving-brick. In fact, it makes an artificial flint, and by the time it is burned it is the same as flint, as you cannot break it. You can readily cut glass with it. It makes a fine material for paving purposes by proper manipulation with different clays. In that way you can make a good paving brick when otherwise perhaps you can not." Mr. Shea, of Decatur, Ill., who has had a large experience in manufacturing street paving-brick from common clay, and who has succeeded in producing a hard, tough, flinty brick, gives his ideas on the subject in the following language : " I admit you must have an intense heat to make a paving-brick, but it is not necessary to have anything pertaining to fire-clay. The further away you can go from fire-clay, in my opinion, the better brick you will have. The clay that will make paving brick is not as scarce as one might imagine. There is a great deal of paving-brick clay all over the country, and it will be discovered as the demand for paving-brick arises." Mr. W. D. Gates, of Chicago, Ill.: " Do not give up your clays too quickly ; do not make up your mind too quickly that you cannot make paving-brick, It may be that just the little item of tempering the brick in the kiln may change failure to success. A man that has clay that does not fuse easily, that stands a high heat, no matter whether it is fire-clay or not, has a fruitful field for experiment before him." Mr. A. 0. Jones, of Zanesville, O.: "The majority of good building-brick clays with different treatments will make fairly good paving-brick for light travel. But to stand the wear and traffic of large cities, and to equal granite and other high-priced and expensive pavements, there must be a careful selection of clays, such as semi-fire-clays or some of the shale clays that will stand a high degree of heat so as to become thoroughly vitrified, and at the same time have the toughness that is neces sary to stand the continuous friction of heavy-loaded teams from and to the freight stations and wharves.