PHYSICS, CHEMISTRY AND ENGINEERING 157 



SOME STRUCTURAL PROPERTIES OF GYPSUM 

 AND OF REINFORCED GYPSUM 



W. A. Slater, University of Illinois 



LIST OF FIGURES 

 Fig. 

 No. Title 



1. Weight of hydrated gypsum mixed with various percentages of water. 



2. Variation of strength of gypsum with age. 



3. Variation of strength of gypsum with continued drying out. 



4. Variation of strength of gypsum with variation of amount ( f gaging 



water. 



5. Effect of continued saturation on strength of gypsum. 



6. Effect of addition of varying amounts of retarder on strength of 



gypsum. 



7. Effect of drying out on bond strength of gypsum. 



8. Effect of amount of water used on bond strength of gypsum. 



9. Stress distribution on a section at center span of reinforced gyp- 



sum T-beam. 



TABLES 



1. Strength of second settle gypsum from several mills. 



2. Results of tests of reinforced gypsum T-beams. 



Recent developments in building construction requiring a 

 light, cheap fire-resisting building material have brought 

 about investigation of the structural properties of gypsum. 



Nearly twenty years ago a reinforced gypsum floor was 

 approved by the City of New York after a fire test at Colum- 

 bia University Testing Station. 1 Similarly, load tests were 

 made on gypsum floor construction early in the history of 

 floor tests. 3 These tests made a creditable showing, but for 

 some reason attention was directed away from gypsum to- 

 ward Portland cement concrete, and it is only recently that in- 

 vestigation of gypsum has been receiving the attention to 

 which the importance of the subject entitles it. 



Engineers' opinions of gypsum seem usually to be based on 

 observations of the gypsum block used for partitions. This 

 block is used only in places where strength is not required 

 and consequently it is designed to secure lightness rather than 

 strength. Of the wet mixture used for this block over 50 

 per cent by weight is water. 



Fig. 1 shows that such a mixture gives a very light wall, 

 approximately three-eighths the weight of Portland cement 

 concrete. Fig. 1 also shows that even with the smallest 



1 Test of Metropolitan floor system, May 20, 1897. See International Associa- 

 tion of Testing Materials, Paper XXVII, by Ira H. Woolson and Rudolph P. 

 Miller. 



J See Eng. News Vol. XXXIV, page 333, Nor. 14, 189S. 



