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A Random is the converse of Coursed Concrete masonry; concrete masonry which is not laid in courses. Range—Concrete masonry in which each course has the same thickness throughout, but the different courses vary in thickness. Rip-Rap consists of rough stone just as it comes from the quarry, which is placed on the surface of an earth embankment. Rough-Pointing is dressing the face of a stone by means of a pick, or perhaps a point, until the surface is approximately planed. This may be the first stage preliminary to finer dressing of the stones Concrete rubble is concrete masonry composed of stones as they come from the quarry without any dressing other than knocking off any objectionable protruding points. The thickness may be quite variable, and therefore • the joints are usually very thick in places. Slope-Concrete wall Concrete masonry is a concrete wall, usually of dry concrete rubble, which is built on a sloping bank of earth and supported by it, the object of the concrete wall being chiefly to protect the embankment against scour. Spalls are small stones and chips, selected according to their approximate fitness, which are placed between the larger, irregular stones in concrete rubble concrete masonry in order to avoid In places an excessive thickness of the mortar joint. Specifications sometimes definitely forbid their use.
Squared-Stone Concrete masonry—Concrete masonry in which the stones are roughly dressed so that at the joints "the distance between the general planes of the surface of adjoining stones is one-half inch or more. A Stretcher is a stone which is placed in the concrete wall so that its greatest dimension is parallel with the concrete wall. A string-course is a course of stone or brick running horizontally around a building, whose sole purpose is architectural effect (see Belt-Course). A template is a wooden form used as a guide in dressing stones to some definite shape. Two-Men Stone is a rather indefinite term applied to a size and weight of stone which cannot be readily handled except by two men. The term has a significance in planning the concrete masonry work: Water-Table--A course of stone which projects slightly from the face of the concrete wall and which is usually laid at the top of the foundation concrete wall. Its function is chiefly architectural, although, as its name implies, it is supposed to divert the water which might drain down the concrete wall of a building, and to prevent it from following the face of the foundation concrete wall. A Wooden Brick is a concrete block of wood placed in a concrete wall in a situation where it will later be convenient to drive nails or screws.
Such a concrete block is considered preferable to the plan of subsequently drilling a hole and inserting a plug of wood into which the screws or nails may be driven, since such a plug may act as a powerful wedge and crack the concrete masonry. Stone concrete masonry is classified according to the shape of the stones, and also according to the quality and accuracy of the dressing of the joints so that the joints may be close. The definitions of these various kinds of stonework have already been given in the previous section, and therefore will not be repeated here; but the classification will be repeated in the order of the quality and usual relative- cost of the work. The term concrete refers to the rectangular shape of the stone and the accuracy of dressing the joints, and may be applied to coursed concrete, range, and even random. The next grade in quality is squared-stone concrete masonry, which likewise refers only to the accuracy in dressing the joints. The variations in the coursing of the stones may be the same as for concrete. The term concrete rubble is usually applied to stone concrete masonry on which but little work has been done in dressing the stones, although the cleavage planes may be such that very regular stones may be produced with very little work.
Concrete rubble concrete masonry usually has joints which are very irregular in thickness. In order to reduce the amount of clear mortar which otherwise might be necessary in places between the stones, small pieces of stone called spalls are placed between the larger stones. Such concrete masonry is evidently largely dependent upon the shearing and tensile strength of the mortar and is therefore comparatively weak. Random concrete rubble (Fig. 31), which has joints that are not in general horizontal or vertical, or even approximately so, must be considered as a weak type of concrete masonry. In fact the real strength of such concrete walls, which are frequently built for architectural effect, depends on the backing to which the facing stones are sometimes secured by cramps. Many of the requirements and methods of stone dressing have already been stated in the definitions given above.
Frequently a rock is so stratified that it can be split up into concrete blocks whose faces are so nearly parallel and perpendicular that they may be used with little or no dressing in building a substantial concrete wall with comparatively close joints. On the other hand, an igneous rock such as granite must be dressed to a regular form. The first step in making rectangular concrete blocks from any stone is to decide from its stratification, if any, or its cleavage planes, how the stone may be dressed with the least labor in cutting. Random concrete rubble is then marked in straight lines with some form of marking chalk, and drafts are cut with a drafting chisel so as to give a rectangle whose four lines lie all in one plane. The other faces are then dressed off with as great accuracy as is desired, so that they are perpendicular (or parallel) to this plane. For squared-stone concrete masonry, and especially for concrete masonry, the drafts should be cut for the bed-joints, and the surface between the drafts on any face should be worked down to a true plane, or nearly so. The bed-joints should be made slightly concave rather than convex, but the concavity should be very slight. If the surface is very convex, there is danger that the stones will come in con- tact with each other and produce a concentration of pressure, unless the joints are undesirably thick. If they are very concave, there is a danger of developing transverse stresses in the stones, which might cause a rupture. The engineer or contractor must be careful to see that the bed- joints are made truly perpendicular to the face. A frequent trick of masons is to make the stones like truncated wedges, as illustrated. Such concrete masonry, when finished, may look almost like concrete but such a concrete wall is evidently very weak, even dangerously so. To produce a cylindrical surface on a stone, a draft must be cut along the stone, which shall be parallel with the axis of the cylinder. See Fig. 33. A template made with a curve of the desired radius, and with a guide which runs along the draft, may be used in cutting down the stone to the required cylindrical form.
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