Granolithic and Wooden Footwalks.
In a paper read before the Engineer’s Club of Philadelphia, Robert A. Cummings treated very interestingly the subject of material for sidewalks, talking particularly of granolithic, and then of an improved wooden pavement.
Granolithic pavement is a patented pavement of large separate blocks. It has a solid founation of well-broken stone or slag, thoroughly rammed to twelve inches deep, on top of which is laid the pavement proper. The first course consists of concrete laid about four inches thick, in propot lion (by measure) of one part of the best English Portland cement to three parts of clean sharp sand and six parts of broken stone that will pass through a two inch ring ; the whole is then well mixed, and water added until it forms a stiff, pasty mass. Having placed this concrete, it is well rammed wi h ordinary street rammers, weighing from 35 to 40 pounds each, after which the final and finishing course is applied, which is about one and a half inches in thickness, and consists of one part of Dyckerhoff’s cement, thoroughly incorporated, while dry, with two parts of crushed granite and the desirable quantity of lamp black for coloring, the crushed granite having been passed through a sieve with one-half inch meshes ; this is then made into paste by mixing well with the requisite quantity of water, which varies somewhat according to the time of year and climate in which it is being laid. This variableness is a necessity for finishing purposes, more especially so when exposed to the hot rays of the sun in summer, and, on the other hand, the necessity for quick setting in winter. ‘ Having then laid the final course, an even surface is made with ordinary plasterer’s ” floats,” and, while it is still ” green,” the whole pavement is rolled with a brass roller so shaped that the surface becomes speckled wish small indentations, and left in this state until sufficiently hard for travel.
In Europe it is quite common to place one-quarter inch soft wood strips between each two stones, to take up the contractions ami expansions caused by a changeable temperature.
The accompanying cut shows a cross-section of granolithic pavement laid by the Norfolk and Western Railroad Company for the platforms and station grounds of the Lynchburg passenger station. The ease with which this pavement can be cleaned, its durability and its low cost of maintenance, are among the more prominent features which especially recommend it for such purposes.
Mr. Cummings thinks that the superiority of a granolithic pavement may be briefly summarized as follows : t. There are but very few joints to collect filth ; 2. From its durability and toughness it produces no dust; 3. It is impermeable to moisture, etc., hence prevents the emission or transmission of unhealthy vapors ; 4. It is easily cleaned.
An objection, however, has been raised that it is too solid, and not sufficiently elastic for contintal walking, and that pedestrians who suffer from the ill effects of flag-stones and brick pavements (to say nothing of the effect upon one’s morality from treacherous loose bricks and mud) require a paving material that is more elastic, more comfortable and less costly. With this in view, an improver! wooden pavement, illustrated herewith, has been designed to combine as many advantages of paving material as possible. It is simple and inexpensive, and the accompanying sketch shows the comparison of such a pavement with granolithic. The first course is five inches thick and of broken stone, the interstices being partly filled with a sandy gravel, thoroughly rammed to an even surface; this is then grouted with a mixture of sand and coal tar until the whole surface is covered, which is virtually the next course. The wearing material is white cedar wood, in blocks 4×5 x 9 inches, breaking joints.
The blocks are pressed into the superfluous grouting material, a portion being squeezed up between them, and any open joints that appear on the surface are to be filled, thus forming virtually a continuous unbroken surface. The advantages of this pavement are asserted to be briefly : 1. Its low first cost ; 2. Its elasticity ; 3. Its durability ; 4. Its low cost of maintenance ; 5. Its general comfort and convenience; 6. Its hygienic qualities ; 7. The ease with which it can be cleaned ; 8. Its impermeability to moisture from below.