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Combined Concrete Curb and Gutter

mortar, plank, partitions, cement, front and sections

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COMBINED CONCRETE CURB AND GUTTER. In recent years the construction of combined concrete curb and gutter built in place has become very general in the smaller cities, and in resi dence districts of larger cities. Such construction is cheap, dur able, efficient, and good in appearance. It is very popular with brick pavement, and with asphalt where the grades are very flat, and is often used with a crushed-stone pavement. Fig. 110 shows the cross section of the usual form. Fig. 111, page 354, shows the form of combined concrete curb and gutter employed in St. Louis, Mo.

Foundation.

A trench is excavated 4 to 6 inches wider than the base of the concrete, and a layer of cinders or gravel 4 to 8 inches thick (usually 6 inches) is laid, flooded with water, and then thoroughly tamped. Upon this foundation is erected the forms in which the concrete is to be laid.

The Forms.

There are two general methods of construct ing these forms: 1. Some contractors lay alternate sections in boxes about 6 feet long, and subsequently place boards against the sections first laid and construct the remaining sections. This plan is more expensive and does not secure as good alignment as the method described below. 2. A continuous line of plank is set for the back of the curb and another for the front of the gutter. These plank are kept in place by stakes on both sides. Partitions are inserted so as to divide the mass into sections 6 or 8 feet long.

Two forms of partitions are in common use. Sometimes these partitions are plank 1i or 2 inches thick, in which case the sections are laid alternately, the partitions being removed before the second series of blocks are formed. In other cases, the partitions are made of steel or - inch thick, and are left in position until the blocks are practically finished. There is but little choice between the two forms of partitions, except that it is difficult to withdraw the steel partitions without chipping the surface coat.

The form for the front of the curb is made by setting a plank 1} or 2 inches thick against the front of the upper part of the partitions and clamping it to the plank at the back of the curb with steel screw-clamps. Of course, the lower edge of this plank is

rounded to make the curve between the face of the curb and the top of the gutter.

The concrete for the base of the gutter is deposited and tamped, and then the mortar for the face of the gutter is applied—all before the form for the front of the curb is clamped into place. After the plank for the front of the curb is in place, a 1-inch plank is placed immediately behind it, and the concrete for the body of the curb is deposited and tamped. The 1-inch plank is then carefully removed, and the mortar for the face of the curb is put into the vacant space. Just as the mortar begins to take its initial set, the board in front of the curb is removed, and the curb and the gutter are troweled smooth.

Mixing and Laying.

The mortar is usually one part of Portland cement to 1 or 2 parts of clean sharp sand.

The concrete may be made of either gravel or broken stone, the usual proportions being either 1 'part Portland cement, 2 parts sand, and 4 parts of unscreened crushed stone, or 1 part cement and 5 or 6 parts of gravel.* To secure durability it is necessary that the surface layer of mortar should be made with Portland cement; and to secure a good union between the layer of mortar and the concrete, it is necessary that the mortar and the concrete should be made with the same brand of cement. Many attempts have been made to lay a coat of Portland cement mortar upon a natural cement con crete; but nearly always the two have separated. It is also neces sary that the mortar coat should be applied as soon as possible after the concrete is laid, so that the cement may set throughout the entire mass at the same time; otherwise there is danger of the two separating. The concrete should be mixed so dry that little or no free water flushes to the surface while it is being tamped. If the water flushes to the top, there will come with it more or less earthy matter which will prevent a firm union of the mortar and the concrete.

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