CHAPTER XVII

STONE BLOCK PAVEMENTS

DEVELOPMENT. Stone block pavement is the oldest known form of permanent pavement. The historical review of the types used prior to about A.D. 1840 has already been treated in Chapter I. As stated in that chapter, Telford, in 1824, was apparently the first to recognize the importance of the smaller size blocks cut in such a manner as to give close joints and the value of a stable foundation. London further developed this type of pavement, mortar joints being first used in 1840, while later, about 1872, a method of construction, using both a concrete foundation and tar and gravel joints, was adopted.

Belgian blocks, so-called because they were first used in Belgium, were similar to a truncated pyramid in shape, having a base of 5 to 6 inches square, a depth of from 7 to 8 inches, the other face having dimensions not more than 1 inch smaller than those of the base. This type of pavement was commonly found in European cities, while in 1859 it became quite common in New York. It was impossible to maintain a smooth surface with these irregular shaped blocks, and ultimately it led to the adoption of the rectangular block pavement. This shape of block was first used in New York City about 1876. Due to the fact that the first Belgian block pavements laid in New York were constructed with blocks of trap rock taken from the Palisades on the Hudson, any trap rock block pavement was called Belgian block regardless of the shape of the block.

In the more recent development of the rectangular stone block pavement more attention has been paid to the accurate cutting and sizing of the blocks, the joint filler, and the foundation. The blocks are generally required to be laid on a concrete foundation and sand, tar and gravel, asphalt and gravel, and cement grout are used as fillers. Within the past few years the use of small block pavements has become more or less extensive

in certain parts of Europe. Both 4-inch cubes and smaller setts, approximating 234-inch cubes, have been employed in this construction.

STONE BLOCKS

THE STONE. The blocks are generally made of granite. Sandstone, quartzite, and trap rock are also employed. The stone should be of such quality that it will resist weathering and will not wear round and smooth under the action of traffic.

The planes of cleavage of granite are such that it is easy to make blocks from it. The trap rocks are harder and tougher than the granites and are not so easily made into blocks. Sandstone blocks are not usually suitable for streets taking an extremely heavy traffic. They do not wear round like the granite blocks, but more uniformly, although sometimes very rapidly. Sandstone cuts into blocks readily. The Medina and Potsdam sandstones which are found in New York State have been used to a considerable extent throughout this State in pavements. In Rochester, N. Y., dressed Medina stone is used with excellent results on the main streets taking a heavy traffic. A large amount of quartzite has been laid in Chicago with good results.

MANUFACTURE OF THE BLOCKS. The majority of stone blocks are made by hand tools. Large blocks of stone are split up into sizes desired by the use of plugs and feathers. The faces of the small pieces are then hammer-dressed until smooth enough to comply with the specifications. The small-sized blocks used in the construction of Kleinpflaster and Durax pavements are cut out by a machine, which is illustrated in Fig. 168.

Considerable care has to be taken in making blocks for a first-class pavement. The blocks should be dressed so as to be rectangular on the faces, having parallel sides and ends with right angle corners. Some specifications do not allow depressions on the face exceeding 1/4 of an inch. If the faces are not all free

from bulges and hollows, it is impossible to get close and even joints in the pavement.

Size of Blocks. The size of blocks is quite variable. In the United States large standard blocks for a first-class pavement are from 7 to 8 inches deep, 3 to 41⁄2 inches wide, and from 8 to 12 inches long. A light block is also used under certain conditions which is from 4 to 41⁄2 inches deep, 31⁄2 to 4 inches wide, and 6 to 12 inches long.

In Liverpool, England, blocks for heavy-traffic streets are 6 inches deep, 3 inches wide, and 5 to 6 inches long. In Birmingham, England, blocks which are approximately 4-inch cubes are used. This same size block has also been adopted in Belfast, Ireland, but it is generally made 6 rather than 4 inches in depth.

The stone blocks used in France are either cubical or rectangular in shape and of very variable dimensions, the lengths varying from 6 to 9 inches, the width from 4 to 8 inches, and the depth from 6 to 9 inches.

In Hungary the stone blocks are somewhat larger than are commonly used in other European countries. The largest blocks are 7-inch cubes; a three-quarter size block, so-called, measures 7 by 7 inches on the face and is 5 inches deep; the conical shape blocks are 7 inches square on the top face and have a bottom face two-thirds the area of the top; the smallest size blocks are 3 to 4-inch cubes.

The blocks for Kleinpflaster and Durax pavements are somewhat similar in size. Those for Kleinpflaster are roughly 24 by 24 by 234 inches in size. The blocks for the Durax pavement are from 234 to 31⁄2 inches in size.

Tests for Block. There are no standard tests for stone block which have been adopted in the United States. The qualities of the stone of which a block is composed, however, can be determined by submitting it to the abrasion, hardness, and toughness tests as made in connection with the tests of broken stone. These tests have been previously described in Chapter IX. The crushing strength of the stone is the only characteristic that is determined by some engineers.

Specification. The following specification which is quoted

from those adopted in 1912 by the Association for Standardizing Paving Specifications will serve to show what are considered to be the requirements for stone blocks suitable for use in a first-class pavement:

"The paving blocks, which shall be of medium grained granite, showing an even distribution of constituent material, shall be of uniform quality and texture, without seams, scales, or discolorations showing disintegration, free from an excess of mica or feldspar, and equal in every respect to the sample in the office of the engineer.

"The granite shall preferably be such as will give above 16,000 pounds per square inch crushing strength, combined with a uniform structure and toughness. The toughness to be determined by the method employed by the Department of Agriculture of the U. S. Government.

"Blocks shall be of the following dimensions, viz., not less than 8 inches nor more than 12 inches long on top, not less than 31⁄2 inches nor more than 41⁄2 inches wide on top, not less than 5 inches nor more than 51⁄2 inches deep.

"The blocks shall be so dressed that, after laying, a measurement of the individual joint shall show a width of not more than 1⁄2 inch at top and for a depth of 1 inch, and a width of not less than 1 inch in any other part of the joint. The head of the block shall be cut so that it shall not have more than 3 inch depression from a straight-edge laid in any direction across the head and held parallel to the general surface of the block.

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"Not more than one drill hole shall show on the head of the block and none on the ends, an allowance of not over an average of one block, showing drill hole on side, shall be permitted to a square yard.

"Care shall be exercised in handling the blocks so that the edges and corners shall not be chipped or broken, as blocks, otherwise acceptable, may be rejected on account of spawling."