If saturation of concrete is assumed to occur, then the following 

 interim guide can be used for strength gain with age. The initial 

 28-day fog-cured strength should be reduced by 10% to account for 

 saturation effects. Subsequent increases of in-situ strength with time 

 may depend on the depth at which the concrete is located. Depth is 

 important because it can influence the degree of saturation. At pre- 

 sent, data are available at depths of a few thousand feet. In such 

 cases, the strength increase relative to the 28-day fog-cured strength 

 appears to be nil at 1 year, 5% at 2 years, and 15% at 5 years. These 

 values of strength-increase-with-age are different from those generally 

 accepted (Ref 14) for on-land concrete of 20% at 6 months and 24% at 12 

 months . 



For cases where the concrete is at a depth of a few hundred feet, 

 it is hard to estimate the strength gain behavior. First, it is unknown 

 how much of the wall thickness will become saturated. It could take 

 months for several feet of thickness to become saturated. If the inter- 

 ior of the structure were to be at a relative humidity of less than 100%, 

 the concrete would never become saturated. However, some of the 

 concrete would be saturated near the outside wall, and that portion 

 would exhibit a strength different from that not saturated. For the 

 saturated concrete the compressive strength should be reduced by 10% 

 to account for saturation effects; then it is probably reasonable to 

 permit a strength increase relative to the 28- day fog-cured strength of 

 nil at 6 months and 5% at 12 months. 



Effect of Reinforcement . The experimental specimens were unrein- 

 forced concrete, whereas any full-scale structure would be reinforced 

 concrete. The reinforcement certainly contributes to stiffening of the 

 wall during bending caused by out-of-roundness . However, under 

 ultimate conditions the contribution of the reinforcement is not easily 

 assessed. 



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