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Construction of Brick Pavements

foundation, sand, surface, bricks, pavement and cushion

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The work to be performed in laying a brick pave ment, after grading and rolling the road bed (see Art. 43), consists in placing the foundation; forming a cushion coat of sand over the foundation; laying the bricks upon the sand cushion; rolling, or ramming, the bricks to a uniform surface and bearing; culling all broken and imperfect brick; filling the joints between the bricks; cleaning the pavement and opening it to traffic.

Foundation. A brick pavement should have a firm foundation. As the surface is made up of small inde pendent blocks, each brick must be adequately sup ported from below, or the loads coming upon it may force it downward and cause unevenness. The wear of the pavement depends very largely upon the mainten ance of a smooth even surface, as any unevenness will cause the bricks to chip on the edges, and also produce impact from the loads passing over the pavement.

The best foundation for a brick pavement is doubt less one of concrete, laid after the manner given in Art. 47. For light or moderately heavy traffic, such as that of the ordinary small city where the road-bed is of firm soil and properly drained, the concrete is usu ally placed 4 to 6 inches thick. If the traffic be very heavy 9 inches may be necessary, and where from any cause the road-bed is not firm it may be advisable to still farther increase the depth.

Under comparatively light traffic a foundation of gravel or broken stone as mentioned in Art. 46 may be used. This foundation should, however, usually be employed only where traffic is light and the road-bed good.

The double-layer pavement (see Fig. 24) consists of a foundation made by placing a layer of sand or gravel 3 to 5 inches thick upon the road-bed, rolling it thoroughly and laying a course of bricks upon it. The bricks are laid flat with their greatest dimension length wise of the street, as explained in Art. 49.

This foundation has been more extensively used under brick pavements than any other, and has often given satisfactory results. It is now largely giving

place to concrete in the better class of work, and in many cases under light traffic its economy is question able, as the layer of gravel would often answer equally well without the lower layer of bricks. The best base to use for a particular work must usually be largely determined by the availability of various materials.

Sand Cushion. The sand cushion consists usually of a layer of sand varying, in the practice of different engineers, from to 2i inches in thickness over the surface of the foundation. The most common prac tice is to make the sand cushion i or 2 inches thick. It should be deep enough to admit of the brick being driven to a smooth surface, and to take up any in equalities in the surface of the foundation and differ ences in thickness of brick. When a very thin cushion layer is employed it is necessary to secure much greater accuracy in forming the surface of the founda tion, and it is much more difficult to uniformly bed the bricks than when the usual thickness is used. It has also been claimed that the thicker sand-bed has a marked tendency to diminish the rumbling of the pavement. This, however, is perhaps rather doubtful.

In forming the sand-bed the sand is spread over the foundation a little deeper than the bed is to be left, and is then drawn off to a smooth surface by the use of a form, cut to the desired shape of the surface, which extends across the street, and slides on the curbs or on stringers laid lengthwise of the street as may be convenient. The making of a good firm bed requires that considerable sand shall be pulled off from all parts of the bed, and the sand should always be two or three inches deep against the front of the form when drawing it to cut the bed. In order to accomplish this, without failing to cut a perfect sur face through the form leaving the guides and riding up on the sand, considerable weight is required on the form when drawing it.

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