Concrete block

“ Walls of concrete chimneys should be not less than 4 inches thick or else they should be reinforced in both directions; otherwise cracking during the setting of the concrete or, later, due to temperature changes or unequal settlement of the foundation is apt to occur. Concrete blocks are not recommended, but if they are used each block should be reinforced with steel running continuously around it and the blocks should be not less than 4 inches thick. They should be lined with the best flue lining. All monolithic concrete chimneys with walls less than 8 inches thick should be lined. ”

“ A moderate degree of roughness or variety in the surface of blocks is, in fact, desirable, and would go far to overcome the prejudice which many architects hold against the smooth, lifeless surface of cement work. Sand and gravel are, in most cases, the cheapest material to use for block work. The presence of a few per cent of clay or loam is not harmful provided the mixing is thorough. Stone screenings, if of good quality, give fully as strong concrete as sand and gravel, and usually yield blocks of somewhat lighter color. ”

“ It is a vertical wall formed of what appear to be massive concrete blocks, but are really the volumes of the Insidecompletuar Britanniaware, the greater number of which are of 32 tons in weight, arranged upon what is known as the sloping block system, and founded upon a rubble mound of stone deposited from barges and levelled for the reception of the blocks by divers. Concrete was then filled in as rapidly as possible until the entire mass, weighing about 9000 tons, had formed, so to speak, an artificial rock or island in the sea, being, in fact, a completed section of the breakwater itself. ”

“ Assuming a strength of 1,000 pounds and a factor of safety of 5, the safe load would be 200 pounds per square inch, or 200 × 192 = 38,400 pounds for the whole surface of the block. Dividing this by the weight of the block, 130 pounds, we find that 295 such blocks could be placed one upon another, making a total height of wall of 222 feet, and still the pressure on the lowest block would be less than one-fifth of what it would actually bear. This shows how greatly the strength of concrete blocks exceeds any demands that are ever made upon it in ordinary building construction. ”

“ The blocks, which are shaped at such an angle that they give the most perfect mutual support, are joined to each other by oaken dowels, and laid on a hard concrete foundation, presenting a level surface, over which the impact is so equally divided, that the whole mass resists the pressure on each particular block; and yet, from being formed in panels of about a yard square, they are laid down or lifted up with far greater ease than the causeway. ”

“ While the mass is plastic I lay or spread the same upon the foundation or bed of the pavement, either in moulds or between movable joists of the proper thickness, so as to form the edges of the concrete blocks, a, a, etc. When the block, a, has been formed, I take strips of tar papor, b, of a width equal, or amost equal, to the height of the block, and place them up against the edges of the block in such a manner that they form the joints between such block and the adjacent blocks. ”

“ Many attempts have been made to use compositions, into which asphalt or cement usually enters, for making blocks or slabs, square or hexagonal, that can be laid down on a concrete foundation. A mosaic of macadam set in an iron frame is fixed by running molten slag into the back of the block. Small square pieces of oak are formed into blocks, end-grain upwards. Staffordshire blue bricks, made with holes to hold wooden plugs, have been used with some success. Broad blocks not firmly fixed down usually become loose and tilt when subjected to traffic. ”

“ The pressed blocks of which they are built show the new freedom conferred by concrete as a building material. Each block has a long right-angle arm extending inward from the middle, and a short arm extending from each end. In laying the blocks in a wall no portion of a block extends through the wall. By leaving the exterior vertical joints open to afford a free circulation of air, no part of a block on one side of the wall touches any block from the opposite side ”

“ Proportions.—There are three important considerations to be kept in view in adjusting the proportions of materials for block concrete—strength, permeability, and cost. So far as strength goes, it may easily be shown that concretes very poor in cement, as 1 to 8 or 1 to 10, will have a crushing resistance far beyond any load that they may be called upon to sustain. Such concretes are, however, extremely porous, and absorb water like a sponge. The blocks must bear a certain amount of rough handling at the factory and while being carted to work and set up in the wall. ”

“ General Hints On Waterproof Qualities.—To obtain good water-resisting properties the first precaution is to make the concrete sufficiently wet. Dry-tamped backs, even from rich mixture, will always be porous and absorbent, while the same mixture in plastic condition will give blocks which are dense, strong, and water-tight. The difference in this respect is shown by the following tests of small concrete blocks, made by the writer. The concrete used was made of 1 part cement and 5 parts mixed fine and coarse sand, by weight. ”

“ Old stone block or brick pavement may be utilized for foundation, provided that the blocks or bricks do not require to 71be taken up and reset, or, if so taken up and reset, that the joints shall be completely filled with grout composed of one (1) part Portland cement and two (2) parts of good sand. Depressions, trenches and holes shall be treated as specified in Section 105.
107. Hydraulic concrete foundation shall be constructed in compliance with the requirements of Sections 28, 29, 30, 31, 32, 33, 34, 35, 36 and 37 of these specifications. Its depth or thickness shall be ... inches. ”

“ In 1906 a like apparatus was used in the construction of a reinforced concrete building in Norfolk, Va. Concrete was elevated in a tower to a hopper, which was capable of being elevated from story to story as the work progressed. The chute attached to the mouth of the hopper by swivel was capable of lateral movement, and supported by block and tackle attached to the top of the tower. ”

“ In fact, in places where stone of any kind is difficult to procure at a reasonable cost, as for instance at Port Said, concrete blocks are indispensable for the construction of breakwaters. Large concrete blocks, moreover, by enabling a comparatively steep slope to be formed with them on the sea side of a mound breakwater, reduce considerably the amount of materials required, especially at exposed sites, and also for breakwaters extended into deep water, such as those of Algiers and Marseilles. ”

“ Dog holes can be made with a pick when the concrete is three or four weeks old. When it is not practicable to use dogs, two-pin lewises can be used. The lewis holes should be cast in the block and should be of larger size than for granite; they should not be located too near the mortar faces. In turning blocks it is necessary to provide some sort of cushion for them to turn on or broken arrises will result. When the work will permit, it is desirable to round the arrises to about a 3⁄8-in. ”

“ The concrete blocks made with 1 to 3 mortar disintegrated in nearly every case, while the stronger ones remained in fairly good condition. The best results were given by concrete containing an excess of very fine sand. Mixing very finely-ground silica, or trass, with the cement proved an advantage where a weak mixture was employed, but in the other cases no benefit was observed. ”

“ It results from diffusion of soluble sulphates of lime and alkalies to the surface. It tends to disappear in time, and rarely is sufficient in amount to cause any complaint.
Properties Of Concrete Blocks—Strength.—In the use of concrete blocks for the walls of buildings, the stress to which they are subjected is almost entirely one of compression. In compressive strength well-made concrete does not differ greatly from ordinary building stone. It is difficult to find reliable records of tests of sand and gravel concrete, 1 to 4 and 1 to 5, such as is used in making blocks ”

“ Another form of foundation takes the shape of Portland cement concrete blocks, and is used chiefly for bridges and in marshy land, &c. In some cases cylinders of brickwork are built, and the centres are filled with blocks of concrete and grouted Concrete piles. ”

“ Blocks Poured From Wet Concrete.—As already stated, concrete made too dry is practically worthless, and an excess of water is better than a deficiency. The above-described machine process, in which blocks are tamped from damp concrete and at once removed, gives blocks of admirable hardness and quality if the maximum of water is used. A method of making blocks from very wet concrete, by the use of a large number of separable molds of sheet steel, into which the wet concrete is poured and in which the blocks are left to harden for 24 {695} hours or longer, has come into considerable use. ”

“ Blocks made from too dry concrete will always remain soft and weak, no matter how thoroughly sprinkled afterwards. On the other hand, if blocks are to be removed from the machine as soon as made, too much water will cause them to stick to the plates and sag out of shape. ”

“ The ideal mixture is one in which all the spaces or voids between the grains of sand are filled with the cement and all the voids in the gravel are filled with the cement-sand mortar. This perfection is seldom attained, because the voids in each lot of gravel and sand vary slightly, and in order to be absolutely safe a little more sand and cement than will just fill the voids are used.
The strongest concrete is not required in every structure, and, in many instances, the cost of it would be unwarranted. ”

“ No. 3 is proposed to be cut out of the solid rock in the eastern slope of the ‘divide,’ by which the maximum strength will be secured with the least expense, concrete will be used only to the extent required to fill cavities, to give the proper dimensions to the various parts, and to give a surface to the blasted rock. The other locks it is proposed to build of concrete, and all of them, No. 3 included, will have a heavy timber lining in the chambers and bays, extending from the top of the walls to 15 feet below the low-water level. ”

“ While this is being done, the broken stone or gravel must be wet, and now it is put on top of the sand and cement and well shoveled together, with just enough water added so that the mass will almost bear the weight of a man.
Concrete is impatient to be hardening, and if it is not put into the right place, it will begin promptly to harden in the wrong place, and nothing can be done with it afterwards. If it is to be made in blocks, the moulds must be ready and the concrete put into them at once and well tamped down. ”

“ Houses built of cement blocks are growing in favor. Cement blocks can be made anywhere by unskilled labor. All that is needed is a competent foreman to direct the making and seasoning of the blocks and laying them in the walls.
The cost of concrete compared to frame or brick structures is, if anything, all things considered, in favor of concrete. Houses built of wood are likely to become increasingly expensive because of the deforesting which is going on in all parts of the United States. ”

“ Bless me! when I come to think of it, it is really wonderful that some of the concrete I have cast in has set at all, and don't believe it can all have set; for, first, the cement was wrong, then the gravel was not gravel, the sand was like road siftings, no trouble was taken to proportion the materials properly, and no mixing was done rightly, only an apology for it. The water was dirty, and used anyhow, and if a lump got a bit stiff it was rolled over, broken up in the trench and watered down below. Some went in like the soup that has balls in it, and we threw the concrete (?) ”

“ If the earthen wall stands firm, only one form, fitting inside the brick wall, is needed. Make this form of narrow flooring securely fastened on the inside to wagon tires or to curved wooden templates, and long enough to extend 2 feet below the point to which the brick are to be removed and 4 inches above the ground level. If the earthen wall shows signs of crumbling, before taking out the brick, dig back the ground to the necessary depth and use an outside form. Lower the forms into place and fill them with 1: 2: 4 concrete. ”

“ Make as few pieces of lumber do the work as you can, and do not drive the Forms full of nails. If you do the Forms will be difficult to take apart without splitting.
Forms must be strong enough to hold the weight of the concrete without bulging out of shape. When they bulge, cracks open between the planks and the water in the concrete, with some cement and sand, will leak out. This weakens the concrete, and causes hollows in the surface which look badly after the Forms are removed. ”

“ In adopting two systems of design of a wall, it is advisable that the change of form be gradual and not made abruptly, or cracks may occur from unequal settlement or load upon the foundations, and also when a concrete bed is used under a wall a lime concrete layer cannot be firmly joined to one composed of more solid and unyielding material, such as Portland cement concrete. Similar walls erected upon different soils are not equally strained, as one earth may scarcely change from the effects of air and water, and another may vary daily according to the weather. ”