TYPES OF KEINFOKCEMENT 137 



The wrought-iron or steel reinforcement, being entirely imbedded in 

 the concrete, is protected from corrosion. Though no reinforced concrete 

 structure is yet old, there is every reason to believe that reinforced 

 concrete is a very durable material. 



As has already been mentioned, metal may be imbedded in concrete 

 with the main object of preventing the formation of large contraction 

 cracks. Such metal is sometimes spoken of as semi- reinforcement. 



Types of Reinforcement. — Ordinary mild steel or wrought iron in the 

 form of round bars can be safely used as a reinforcement. Special 

 indented, or deformed bars can be obtained, the object of the indentations 

 or deformations being to improve the bond between the concrete and the 

 steel. Plain round bars are, however, quite good enough for all purposes 

 for which reinforced concrete is likely to be used on the farm. Expanded 

 metal reinforcement is made by taking sheet steel, and perforating it all 

 over with slits in such a way that, on the plate being expanded by a 

 pull at right angles to the slits, a diamond mesh-work is the result. 

 Wire mesh reinforcement is a woven wire fabric, which generally consists 

 of a series of parallel main wires, connected by thinner wires woven 

 around them, the whole forming a very open-meshed fabric. This type 

 of reinforcement should be inserted in the concrete so that the main wires 

 lie parallel to the direction of greatest stress (see Fig. 117). 



Care should be taken to insert reinforcement in the exact position 

 specified, or shown on the drawings. In using separate bars for rein- 

 forcing, attention must be paid to having the rods properly held, so that 

 they may not be displaced while the concrete is being jogged and rammed 

 into place. 



When bars are used for reinforcing, they are generally inserted in two 

 systems of bars, which cross each other at right angles. Thus we may 

 have one system of horizontal bars and another of vertical bars. The 

 horizontal bars should be lashed to the vertical bars, where they cross the 

 latter, by soft tying wire. 



Since bars of unlimited length cannot be obtained commercially, 

 it often becomes necessary to splice two or more bars together. Such 

 bars may simply be overlapped. The extent of overlap should be not 

 less than fifty times the diameter of the bars, and the join should be 

 securely bound by soft tying wire. If the ends of the bars be turned 

 over to form anchors in the concrete (Fig. 175) an overlap equal to 

 25 diameterB will suffice. 



