CONCRETE 



1527 



CONCRETE 



piers, abutments and superstructure of bridges, 

 for dams and for lining tunnels. Architects 

 are employing it for dwellings and apartment 

 houses, factories, office buildings, stores and 

 various other structures. It can be run into 

 molds for making ornamental work, made into 

 blocks for the construction of dwelling houses, 

 and built into solid walls for large buildings, 

 grain elevators, bridges, dams, foundations and 

 fortification walls. The fortifications of New 

 York harbor and the foundations for the great 

 guns behind them are of concrete, and the 

 locks of the Panama Canal are of this same 

 material. In 1916 an ocean-going vessel made 

 of concrete was launched in Sweden. 



Reinforced Concrete. Concrete can resist 

 great pressure, but pulls apart very easily. In 

 the article BRIDGE will be found an illustration 

 showing that a beam may break by pulling 

 apart on the under side. For this reason steel 

 rods are anchored in walls and floors of a con- 

 crete building before the concrete is poured 

 into the molds; the rods are thus buried in 

 the concrete and prevent pulling apart. For 

 strengthening floors two sets of rods are used, 

 those of one set crossing those of the other at 

 right angles. The rods are secured to the walls 

 and usually fastened together with wires at 

 the points of intersection. In the construction 

 of pillars a sort of frame consisting of vertical 

 rods and hoops is used. The steel work is put 

 in place and the concrete is poured around it. 

 When the cement hardens a firm, strong struc- 

 ture is the result. 



Concrete Blocks. Concrete blocks are made 

 in molds and are hollow. They are used for the 

 walls of dwellings, for which they form a very 

 desirable material. Being hollow, they contain 

 a dead-air space, which protects the interior 

 from frost. The houses of Morgan Park, near 

 Duluth, Minn., a village built by the United 

 States Steel Corporation for their employees, 

 are constructed entirely of concrete blocks. 



Mixing the Concrete. For small structures 

 the mixing may be done by hand, the work- 

 men using shovels, but for most work mixing 

 machines are employed. The best of these 

 machines receive the raw material at one end, 

 and deliver the prepared concrete at the other. 

 Machines of the latest pattern use compressed 

 air for mixing. 



Completing the Structure. Molds for hold- 

 ing the semi-fluid concrete are first put in 

 place. They may be of wood or steel, but 

 must be so constructed that they can be re- 

 moved easily when the concrete has set. The 



concrete is taken from the mixer in wheel- 

 barrows, carts, cars drawn by locomotives, 

 elevators or other devices, and carefully 

 poured into the molds. Since the cement be- 

 gins to change as soon as it is wet, the concrete 

 must be put in place as fast as it is mixed. 

 In the construction of high buildings an end- 

 less belt to which buckets are attached is used 

 for carrying the concrete to the upper stories. 

 The floors in such buildings are supported on 

 temporary wooden floors which are held in 

 place by studding until the concrete has 

 hardened. 



Concrete Roads. Concrete forms one of the 

 most desirable materials for surfacing streets 

 and country roads. It is laid on a firm foun- 

 dation of sand or gravel and allowed to dry 

 slowly, so that it becomes very hard. When 

 surfaced with a coat of asphalt it makes an 

 ideal street. See CEMENT; ROADS AND ROAD 

 BUILDING, for comparative cpst of various kinds 

 of paving material. 



How to Build a Concrete Foundation. To 

 build a concrete foundation for the small house 

 described in the article CARPENTRY, excavate 

 a trench to a line below the depth to which 

 frost penetrates. The trench must be enough 



A NEW USE FOR CONCRETE 

 Concrete ties for railroads are cheaper and 

 more durable than wooden ties. 



wider than the wall itself for the work to 

 be easily done. With strong planks, across 

 which are nailed upright 2 x 4's every two feet, 

 make a wall for each side of the mold. Set 

 the two walls in place in the trench with the 

 smooth sides inward. As the concrete when 

 poured in will tend to thrust the forms apart, 

 they should be tied together at intervals of a 

 few feet with pieces of wood or with wire. 

 Two wires set close together can be tightened 

 the proper amount by inserting a stick be- 

 tween them and twisting. The forms should 

 also be strengthened from the outside by diag- 

 onal braces nailed to stakes driven in the 

 ground. Mix the sand, cement and stone in 

 small quantities upon a mixing board about 

 six feet square, adding the water a pailful at 

 a time. Put the concrete in the molds as fast 

 as it is mixed. 



