CHAPTER XV 

 CONCRETE CONSTRUCTION 



Concrete is a combination of Portland 

 cement, sand, crushed stone or gravel and 

 water, thoroughly mixed and then allowed 

 to set or harden. 



Portland cement, or cement, as it is now 

 commonly known, is manufactured by burn- 

 ing and grinding together- limestone and 

 clay, or shale, in certain proportions. It de- 

 rives its name, Portland cement, from its re- 

 semblance to Portland stone. It is also 

 sometimes known as hydraulic cement, or 

 building cement. 



Concrete has wellnigh revolutionized 

 building practice in the last 25 years, but in 

 no case has it displaced masonry to a greater 

 extent than in greenhouse construction. 

 Formerly, the walls of a greenhouse were a 

 source of much trouble, because of their 

 rapid deterioration, but it was soon found 

 that when concrete was used tliey be- 



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