STRENGTH OF CEMENT MORTAR AND CONCRETE. 



295 



in tension reinforced with bars of Bessemer steel at ages 

 of from 28 days to 90 days. 



Comparing the deformations and breaking weight of a 

 test piece reinforced with a plain test piece not reinforced, 

 it will be seen that the increase in strength is very marked 

 in the case of the piece reinforced with five bars, being 

 about 2*3 times that of the plain pieces. The increase with 

 four bars is very small compared with the increase with 

 one bar. The decrease in extensibility, and therefore the 

 increase in the coefficient of elasticity is also disproportion- 

 ately low with the four bar reinforcement, probably due 

 to the centre of the specimen being relatively weaker 

 than the exterior. The results are summarised in the 

 following table : — 



Table III. — Showing the stresses producing deformations 

 expressed as multiples of - 00004 of an inch in reinforced tension 

 pieces compared with similar pieces not reinforced. Mortar 

 aged 3 months, 1 cement to 3 sand. 



Extension in 

 0-00004 inch. 



Plain, lb. 

 per sq. inch. 



Reinforced lb. persq. inch. 



□ 







50 







1 



48 



70 



65 



5 



109 



148 



150 



193 



10 



175 



269 



227 



330 



11 



184 



296 



250 



353 



14 







279 



421 



16 









481 



Breaking stress 



219 



281 



301 



516 



The extensions are reduced in consequence of the adhes- 

 ion of the mortar to the steel rods. In every case the 

 instantaneous coefficient of elasticity diminishes as the 

 load increases, the curve being convex to the axis of stresses 

 but the reinforced are slightly flatter than the plain pieces, 

 the five bar reinforcement curve being practically straight. 



Compression Tests. — The compression tests were made 

 on prisms 12 inches long by 6 inches by 6 inches (Fig. 9), 



