part than temperature, but can be obviated by use of 

 steel. 



Stone should always be thoroughly wetted before gaug- 

 ing. Concrete should always be kept damp, while setting, 

 thus allowing equal setting. 



Cement should be the best, finely ground and cool. Ag- 

 gregate pwoper size and perfectly clean. A lean, dry con- 

 crete is likely to form lines of cleavage between successive 

 layers. 



When acid or alkaline solutions are present in sand the 

 sand should not be used. 



If a steel structure must be protected with concrete, 

 it is more economical to use reinforced concrete. 



In making tests, the materials should not be too severely 

 strained during the initial stages, as the resistance in- 

 creases with the age. Most building authorities require three 

 times the maximum load for which the structure is designed. 

 Three months should expire before a test is made. * 

 BEAMS. 



Steel is placed in beams to assist the concrete in ten- 

 sion, shear and sometimes compression. Steel in con- 

 crete beams is never itself in shear. 



Stirrups and the bent bar take the shear not taken by 

 the concrete. The portion of the bent bar at the top and 

 ends of beam takes the tension due to negative moment. 

 The straight bars in the bottom at the center take the 

 tension and at the ends compression. When the concrete 

 is unable to take the entire compression, the upper 

 straight bars are added and inverted U's are used, or 

 bars fastened with lower bars in some manner. Steel 

 should be placed in the tops of all roof beams and girders. 



For various systems see "Reinforced Concrete," by 

 Charles F. Marsh. 



CEMENT. 



Quick setting ce.ments are generally used for pipes, 

 reservoirs, etc. Slag cements, unless burnt after the 

 mixing of the ground ingredients, should not be used. 

 They are not as strong as Portland cements. Slag cements 

 are good under water, but unlit for air. 



A good brand of Portland cement passing the specifica- 

 tions of the American Society of Testing Materials should 

 be used. 



SAND. 



Grains passing a sieve of meshes 1-5 x 1-5 in. is consid- 

 ered sand. 



The following characteristics have been observed: 



