Upon discharge from the pipe the concrete should be capable of 
maintaining its plastic cohesive consistency and not segregating either 
by washing out of cement or settling of coarse aggregates. By "structural 
grade" quality is meant that concrete will develop a 28-day compressive 
strength of say at least 2,500 psi in the deep ocean environment and 
that the concrete have good durability. 
Concrete Mixture Design 
Requirements. The desired concrete properties are: (1) that the 
fresh concrete be pumpable and pipeable under high pressure at discharge 
rates of 30 to 50 cu yd/hour or greater, (2) that the concrete on dis- 
charge at the seafloor will form into a coherent, consolidated mass with 
fairly steep slopes, and (3) that the concrete will develop strength and 
other properties of structural grade concrete in the deep ocean environ- 
ment. 
The fresh concrete will need to be sufficiently plastic and cohesive 
to pump and to flow down the long pipe without bleeding, segregation or 
line blockage, and to have resistance to flow that will limit the maximum 
velocity to not more than about 7 to 10 ft/sec. The pumpable mix may 
need to have greater flow resistance (friction head loss) than usual 
state-of-the-art mixtures in order to use larger diameter pipes to 
provide the desired flow rates. Example velocities are shown in Table 4 
for flow rates of interest in 3- to 4-in. ID pipes. 
Materials. Concreting materials are cement, fine aggregates, 
coarse aggregates, water and admixtures. Portland cement having a 
tricalcium aluminate (CA) content between 4 and 10% should be used. 
Normal weight, well-rounded stone should be used for the fine and coarse 
ageregate. For most cases, the water should be potable although seawater 
may be used. Various admixtures can be used such as low water loss 
admixtures of cellulose compounds or similar patented organic admixtures. 
Bentonite in small quantities will improve cohesiveness. Other inorganic 
materials such as silica flour, pozzolan and flyash may also improve 
cohesiveness. However, air entrainment should not be used because the 
high pressures will collapse the air bubbles and alter the consistency 
of the mix. Set retarders may be needed to prevent premature set or to 
control temperature rise due to cement hydration, especially for very 
large pours. 
Proportioning the Concrete Mixture. Mixtures will be proportioned 
by the minimum voids approach so that all voids are filled and excess 
water made available so that a saturated mix can be maintained. The 
water/cement ratio will be about 0.45 or possibly greater to assure the 
saturated condition. Cement content will be approximately 7 sacks per 
cubic yard. The maximum size of coarse aggregate will be equal or less 
than one quarter the pipe inside diameter and will be limited to a 
maximum size of three quarter inches in most cases. The fine aggregate 
ratio will be about 45 to 50%. The fine aggregate gradation will conform 
to ASTM Designation C33 with the additional requirements that between 15 
21 
