PORTLAND CEMENT COISTCEETE ROADS. 47 



AVlien the average temperature is below 50° F. it is better to omit 

 covering and ponding, and sprinkle the pavement only when the con- 

 crete shows signs of drying out too rapidly. Sprinkling night and 

 morning will usually be sufficient; it should be omitted altogether 

 when there is danger of freezing. 



PLACING CONCRETE IN FREEZING WEATHER. 



Concrete pavement construction should not be attempted during 

 freezing weather. Satisfactory results can not be obtained, and the 

 expense of attempting to heat the water, the aggregates, and the fin- 

 ished work is not justified unless only a very short length of pavement 

 is necessary in order to complete an important piece of work. If 

 danger of freezing develops after the concrete is laid and before it 

 has developed a hard set, the pavement should be protected by means 

 of a heavy layer of straw, covered with canvas. Concrete should not 

 be placed upon a frozen subgrade, and should not be mixed and placed 

 when the air temperature is below 35° F. 



ORGANIZATION AND EQUIPMENT. 



When it is considered that from 50 to 60 per cent of the total cost 

 of constructing a concrete pavement is chargeable to the equipment 

 and labor employed in doing the work after the materials are deliv- 

 ered at the unloading plant, the importance of proper organization, 

 proper equipment, and economical methods becomes clearly apparent. 

 Failure to give these features proper consideration may easily result 

 in adding from 10 to 25 per cent to the cost of a concrete pavement, 

 and has no doubt frequently caused contractors to sustain a net loss 

 on projects where profits might have been made. 



It is not the province of this bulletin to furnish detailed rules for 

 the guidance of contractors in planning and executing their work, 

 but it seems desirable to discuss briefly a few important points which 

 contractors and engineers in charge of force account work should con- 

 sider in concrete pavement construction. The points which are of 

 most importance and to which the discussion will be confined are con- 

 cerned first with the proper order and progress of the work ; second, 

 the selection of ec|uipment ; and, third, the amount of capital necessary 

 to carrj^ on the work economically. 



ORDER AND PROGRESS OF THE WORK. 



In constructing a concrete pavement it is especially desirable that 

 the work of mixing and placing the concrete shall proceed without 

 unnecessary interruption after it is begun. When the mixer is per- 

 mitted to stand idle for even a few days, the force of laborers em- 

 ployed in operating it will usually become more or less disorganized 

 and a certain amount of loss and unsatisfactory work will generally 



