Variations in wall thickness and mean radius, R, are shown around the 

 circumference. The average R was 26.03 ± 0.05 inches (661 ± 1 mm). 

 The magnitude of the standard deviation was mostly from the lack of 

 accuracy in measuring the radius with the steel rule. 



CONCRETE MATERIALS 

 Mix Design 



Concrete was batched and supphed by a transit mix company. 

 Each delivery consisted of 2.0 yd^ (1.5 m^) of concrete. The mix was 

 designed for 6,000 psi (41 MPa) at 28 days. The proportions of cement 

 to sand to aggregate were 1:1.96:2.22, respectively. The cement 

 content was 676 Ib/yd^ (401 kg/m^). Water-to-cement ratio averaged 

 0.55. Slump at the time of placement controlled the total water content, 

 and the slumps averaged 3-3/4 ± 1/4 inches (95 ± 6 mm). 



Portland, low alkali, type II cement was used along with a water- 

 reducing admixture, Zeecon H, at a rate of 6 ounces (0.17 kg) per 100 

 pounds (45.4 kg) of cement. The sand and aggregate were from the 

 Santa Clara River Basin. Maximum aggregate size was 3/8 inch (9.5 

 mm), and the aggregate underwent heavy media separation. 



A summary of the concrete properties is given in Table B-3. The 

 concrete compressive strengths were measured at 7 and 28 days and at 

 the time of testing. Stress-strain curves were obtained from numerous 

 specimens. Several modulus parameters are listed in Table B-3, along 

 w^ith the ultimate strain and Poisson's ratio. Figure B-7 shows repre- 

 sentative stress-strain curves for 7,000 and 8,000 psi (48 and 55 MPa) 

 concrete. 



Expansive-cement grout, used as a packing material between the 

 stiff eners and concrete wall, had mix proportions of one part portland 

 cement type K, one part San Gabriel River sand between sieve sizes 4 

 and 16, one part San Gabriel River sand between sieve sizes 16 and 30. 



54 



