PORTLAND CEMENT CONCRETE ROADS. 23 



10 feet center to center, extending an equal distance into each sec- 

 tion of the pavement. The metal joint may either be punched or 

 slotted to provide for the reinforcing steel. When the surface of 

 the pavement cracks above the submerged joint, the crack is fdled 

 with bituminous material, 



STEEL REINFORCEMENT. 



Steel reinforcement in the past has been used in concrete pave- 

 ments, primarily to prevent excessive cracking. For this purpose 

 it has been customary to use wire mesh or expanded metal weigh- 

 ing from 25 to 40 pounds per hundred square feet. Equally satis- 

 factory results, however, can be obtained by the use of ^-inch de- 

 formed bars spaced 24 inches center to center in both directions. 

 This reinforcing should be placed not less than 2 inches from the 

 finished surface of the pavement and should extend to within 2 

 inches of all joints, but not across them. Adjacent lengths of wire 

 mesh or expanded metal should be lapped from 4 to 8 inches. For 

 ease in handling, the wire mesh or expanded metal should be ob- 

 tained in flat sheets. The use of this kind of reinforcement will 

 add from 30 to 60 cents per square yard to the cost of the pavement 

 and this additional cost is no doubt responsible for the fact that con- 

 crete pavements have not generally been reinforced in the past. Re- 

 inforcement of this type, moreover, does not entirely prevent cracks, 

 but distributes them and keeps them small. 



Under very severe traffic conditions and for pavements laid on 

 exceptionally soft subgrades which cannot be materially improved, 

 reinforcement may be necessary to give greater strength to the pave- 

 ment by distributing the load over a larger area. Deformed bars 

 should be used for this reinforcement and the percentage of rein- 

 forcement required will depend on the traffic loads, the condition 

 of the subgrade, and the range of temperature and the variation in 

 percentage of moisture. The reinforcement should preferably be 

 placed both at the top and the bottom of the pavement and may vary 

 from I to f inch bars spaced from 18 to 24 inches center to center 

 in both directions. Reinforcement to give added strength to the 

 pavement is rapidly gaining favor among engineers, and it is now 

 being extensively used in localities where a large volume of heavy 

 traffic is to be expected. 



Another form of pavement reinforcement — circumferential rein- 

 forcement — consists of f-inch bars, placed half way between the top 

 and bottom of the pavement, approximately 6 inches from the edges, 

 and completely around the slab. This form of reinforcement gives 

 added strength at the edges where cracks usually begin, and on a soft 

 subgrade serves to hold the pavement together should cracking occur. 



