10 



BULLETIN 532, U. S. DEPARTMENT OF AGRICULTURE. 



GRAVEL CONCRETE WITH HYDRATED LIME. STORED IN AIR. 



Curve 557 on figure 8 shows the contraction of a 1:2:4 gravel concrete 

 specimen in which 15 per cent of hydrated lime was substituted for cement. 

 This specimen was cured indoors and allowed to dry out immediately after 

 molding. Here again, as in the case of the ordi- 

 nary concrete specimens, we have a progressive 

 contraction, the maximum amount being about 

 0.00045 inch. This is somewhat less than in the 

 specimen untreated with hydrated lime. As but 

 one specimen ' was measured, no claim can be 

 made that the hydrated lime aided in decreasing 

 the contraction. 



TAR-COATED SPECIMEN. 



It is reasonable to expect that any application 

 of more or less waterproof material to the sur- 

 face of the concrete will greatly retard the ab- 

 sorption of moisture, or. if the concrete be 

 already wet. will prevent it from drying out 

 rapidly. In order to determine the effect of 

 such a coating on the change in length of con- 

 crete, a mixture of 1:2:4 concrete, having a 

 crushed gneiss aggregate, was prepared, and 

 measurements were started two days after 

 pouring. It was then immersed in water and 

 the measurements continued. At the end of 13 

 days the specimen was removed from water and, 

 after surface drying for one day, a hot applica- 

 tion of vertical retort tar was made. Note that 

 after 13 days' expansion continued slightly, al- 

 though the specimen had been removed from 

 the water and coated with tar, while at the end 

 of about 30 days this expansion ceased and a 

 slight contraction began. However, the speci- 

 men was still somewhat expanded up to the 

 end of 150 days, after which it contracted very 

 slowly. The tar coating evidently served to re- 

 tain the moisture in the concrete for a con- 

 siderable length of time and thus kept it ex- 

 panded. 



REINFORCED CONCRETE SPECIMENS. 



001 





























OSl 



















1 





i 







v 2 ooi 



* ui 



Ul O 



z < 

 o 



0C 

 o 







I 













Ik 



z 



) 





or 







Ul 



I 



^ 05 

 K 















1- 



) 



Of 



x 











> 







" 











four specimens were made up of 1 : 2 : 4 gravel 

 concrete containing 0.G1 per cent, 1.2 per cent, 

 and 1,8 per cent of steel. These specimens were 

 allowed to dry out in the air of the laboratory, 

 and measurements were taken at frequent in- 

 tervals. The plain gravel specimens showed a 

 maximum contraction of only 0.035 per cent at 

 the aire of 6 months, as compared with 0.06 per 



cent Cor I he crushed gneiss specimens previously reported. This difference in 

 contraction is not due necessarily to the different aggregates. The specimens 

 containing 0.G1 and 1.2 per cent steel showed a contraction of only 0.02 per cent, 



KOUVHaOd30 ilMD 



