PORTLAND CEMENT CONCRETE ROADS. 59 



in about 100 seconds. In order to apply a tar of this kind satisfac- 

 torily, it is necessary that it be heated to about 225° F. 



The repair equipment may consist of a small portable tar kettle, 

 a light truck, pouring pots, wire brooms, hammers, and stone chisels. 

 The tar kettle is usually hauled by attaching it to the rear of the 

 truck. 



When it becomes necessary to renew any portion of the pavement 

 with concrete, that portion should be entirely closed to traffic, and the 

 concrete should be mixed, placed, and cured in the same way as a 

 new pavement. The edges of the old concrete should be thoroughly 

 cleaned and coated with neat cement mortar before the new concrete 

 is placed. 



A properly constructed concrete pavement ought to wear down uni- 

 fonnly and develop few defect's. Poorly constructed and poorly 

 maintained joints are probably responsible for more defects of the 

 kind described than can be attributed to any other one cause. For 

 this reason the joints should receive very careful attention at the time 

 of construction. 



RESURFACING OLD CONCRETE PAVEMENTS. 



Under certain traffic conditions it may be necessary at tmes to 

 resurface old concrete pavements so as to provide an additional thick- 

 ness of pavement for the increased traffic. The thickness of the 

 resurfacing layer should be not less than 3 or 4 inches at any point, 

 and the concrete should be mixed in the proportions of 1 : 1^ : 3, using 

 a coarse aggregate graded from | inch to 1^ inches in size. Steel re- 

 inforcement weighing at least 25 pounds per 100 square feet, placed 

 in the middle of the resurfacing layer, should preferably be used 

 where the resurfacing is to be 3 inches thick. If the resurfacing 

 layer is to be 4 inches thick, it is not believed that any reinforcement 

 is necessary. Where an old concrete pavement is to be resurfaced, 

 it should be thoroughly cleaned and all the bituminous filling used 

 to cover cracks and small holes removed. The new concrete is placed 

 and finished in the manner previously described for concrete pave- 

 ments. Joints should be provided in the resurfacing layer directly 

 over those in pavement below. The service records of a number of 

 resurfaced concrete pavements indicate that it is immaterial whether 

 or not a bond is secured between the two layers of the concrete. 



