Unit Weights 



Various unit weights for the concretes were obtained. Figures 10 

 through 13 show the unit weights as bar charts in comparing PFA and 

 regular lightweight concrete. The environmental storage condition of 

 30% RH for 17 days after fog curing for 28 days did not produce a uni- 

 formly dry concrete throughout the specimens, so these unit weights have 

 little meaning. The manufacturer's mix design information indicated 

 that the approximate air-dry weights for the regular lightweight concrete 

 would be 92, 94, and 95 pcf for Mix no. 1, 2, and 3, respectively. It 

 was estimated that Mix no. 4 would be about 92 pcf because of the large 

 proportion of coarse aggregate. 



The air-dry unit weights for the PFA concrete were about 103, 106, 

 108, and 110 pcf for Mix no. 1, 2, 3, and 4, respectively. 



The freshly mixed unit weights averaged about 112 pcf for the 

 regular lightweight concrete where the aggregates were totally saturated 

 before the concrete was mixed, while the PFA concrete had an average 

 109 pcf. The PFA was not water-saturated prior to mixing the concrete, 

 which explained the lower densities; air voids had remained in the 

 aggregate and about 10% of the original void volume was not filled with 

 polymer. 



The in-air unit weights for saturated concrete are shown in Figures 

 10 through 13. In the saturation procedure pressure was 500 psi for 14 

 to 17 days. On the average, the PFA concrete showed a unit weight 

 increment of 0.7 pcf greater than that of the regular lightweight concrete. 

 Theoretically, the increment should have been from 0.8 to 1.3 pcf because 

 the specific gravity of polymer is 7.5% greater than that of seawater. 

 In any event, the unit weight differences between the materials were 

 small . 



In summary, the unit weights for the regular lightweight concretes 

 changed from about 94 to 114 pcf when going from the air-dry condition 

 to the water-saturated condition. The high strength PFA concrete (Mix 

 no. 3 and 4) showed unit weights that changed from 109 to 115 pcf when 

 going from the air-dry to the water-saturated condition. 



DISCUSSION 



The significance of the test results is clear when compared to 

 similar data for normal weight concrete. The advantage of using light- 

 weight concrete in the ocean is to save weight. In a saturated condition, 

 regular lightweight and PFA concrete have the same unit weight, so can 

 be considered as lightweight concretes having a saturated unit weight of 

 115 pcf. 



Normal weight concrete has an air-dry unit weight of about 145 pcf 

 (without steel reinforcement) and a saturated unit weight of about 150 

 pcf. If lightweight concrete is used in place of normal weight concrete 

 for such applications as the hull and superstructure of a floating 

 platform, the weight saving is about 30% (using 145 pcf for normal 



