93. Although these do not come under the heading of foundations, they are more nearly related to that class of work than to any other, and may therefore be described here.
When large slabs of stone can be economically obtained, they make, in the long run, the most economical pavement, and one that is about as satisfactory as any.
A smoother pavement may be made with cement, and one that will be practically imperishable, but should there ever be occasion to cut through the pavement, or to change the grade, the cement and concrete must be destroyed, while the stone nagging can be taken up and relaid, either in the same place or used somewhere else. A stone sidewalk can also be repaired easier than either of the others.
Stone Pavements. - As a rule only stones that split with comparatively smooth and parallel surfaces can be economically used for pavements, for, if the surface of the stone has to be dressed, it will generally be more economical to use concrete and cement or hard bricks.
For yards and areas, flagging from 2½ to 3 inches thick is commonly used, the edges of the stones being trimmed so that the stones will be perfectly rectangular, and the joints between them straight and from 1/8 to 3/8 inch in width.
The stones should be laid on a bed of sand not less than 2 inches thick, and the edges should be bedded in cement, as shown in Fig. 51, the cement extending some 3 or 4 inches under the stone. On completion the joints should be thoroughly filled with 1 to 1 cement and fine sand, and struck smooth with the trowel.
In localities where the soil is dry and not affected by frost, as in Colorado, New Mexico, etc., the cement is generally omitted entirely the stones being simply bedded in sand and the joints filled with fine sand.
This answers very well in those localities, but after a time grass and weeds commence to spring up through the joints in yards and private walks, so that for first-class work bedding in cement should be specified.
Stone sidewalks are generally laid on a bed of sand, with the joints in the better class of work bedded in cement. The stones, when 5 feet long, should be at least 3 inches thick, and if 8 feet long, 5 or 6 inches thick. The best sidewalks are laid in one course, unless exceptionally wide.
In localities where the ground is affected by frost, as it is in most of the Northern States, the stones, if merely laid on a bed of sand, are sure to become displaced and out of level within one or two years. To prevent this, flagging stones, in front of business buildings at least, should have a solid support at each end.
Fig. 52 shows the manner in which this is generally provided, and also the way in which the curb and gutter is supported. The curbstone should be at least 4 inches thick, and on business streets 6 inches.
The dwarf wall should be about 14 or 16 inches thick and carried below the frost line.
If the sidewalk is laid in two courses a slight wall of brick or stone should also be built under the middle of the walk to support the butting ends of the stones.
Cement sidewalks are extensively laid in the Western States, even in localities where excellent flagging stone is abundant and cement rather dear.
The cement walks are preferred on account of the smooth and even surface which they give. When properly laid they are also very durable. Cement walks, however, should only be laid where there is no danger of the grade being altered, and after the ground has become thoroughly settled and consolidated.
The durability of the walk depends principally upon the thickness of the concrete and the quality of the cement.
For first-class work cement walks should be laid as follows:
The ground should be leveled off about 10 inches below the finished grade of the walk and well settled by tamping or rolling. On top of this a foundation 5 inches thick should be laid of coarse gravel, stone chips, sand or ashes, well tamped or rolled with a heavy roller. The concrete should then be prepared by thoroughly mixing 1 part of cement to 1 part of sand and 3 of gravel, in the dry state, then adding sufficient water from a sprinkler to make a dry mortar. The concrete should be spread in a layer from 3 to 4 inches thick, commencing at one end, and should be thoroughly tamped. Before the concrete has commenced to set the top or finishing coat should be applied, and only as much concrete should be laid at a time as can be covered that day. If the concrete gets dry on top the finishing coat will not adhere to it. The top coat should be prepared by mixing 1 part of high grade Portland cement with 1 part of fine sand, or 1 part clean, sharp, crushed granite (the latter is the best). The materials should be thoroughly mixed dry, and water then added to give the consistency of plastic mortar. It should be applied with a trowel to a thickness of 1 inch and carefully smoothed and leveled on top between straight-edges laid as guides. Used in the above proportion, one barrel of Portland cement will cover about 40 square feet of concrete. After the walk is finished it should be covered with straw to prevent it drying too quickly.
For brick paving see Section 381.