In summary, the in-place cost of PFA concrete is about 30% greater 

 than that of normal weight concrete while the weight saving is 40%. 

 Only an economic analysis of individual projects can show whether the 

 use of PFA concrete is cost beneficial. 



FINDINGS 



1. The maximum compressive strength after 28 days of fog curing 

 was 6,580 psi for PFA concrete as compared to 5,200 psi for regular 

 lightweight concrete. This high strength mix design of PFA concrete was 

 26% stronger than that of regular lightweight concrete. 



2. The maximum splitting tensile strength of PFA concrete was 

 520 psi or 4% greater than that of regular lightweight concrete. 



3. The failure mode in compressive and tension for PFA concrete 

 was a bond failure between cement and aggregate while the regular light- 

 weight concrete had the aggregate particles fail. Thus, strength in- 

 creases with age can be expected from the PFA concrete while the regular 

 lightweight concrete had attained its limit. 



4. The elastic modulus of PFA concrete was, on the average, 2.1x10^ 

 psi which was 4% greater than that of regular lightweight concrete. A 

 Poisson's ratio of 0.25 was essentially the same for both types of 

 concretes . 



5. Both PFA and regular lightweight concrete have a saturated unit 

 weight averaging about 115 pcf. For undersea applications, a weight 

 saving of 40% is realized if either of these concretes replace normal 

 weight concrete. Although PFA concrete costs about nine times that of 

 normal weight concrete, the in-place structural cost is only about 30% 

 higher. 



ACKNOWLEDGMENTS 



The assistance of the Brookhaven National Laboratory, and in par- 

 ticular Mr. Ron Webster, for impregnating the aggregate is acknowledged. 

 Also, the assistance of our colleague, Mr. Robert Rail, is appreciated. 



