and 30% pass the number 50 sieve and 5 to 10% pass the number 100 sieve 
and that the fineness modulus of the fine aggregate be in the range of 
2.4 to 3.0. The coarse aggregate gradation will conform to ASTM Desig- 
nation C33 as close to the middle range as feasible. The combined 
aggregates will be well graded with no gap grading. The air content 
will be minimized (Ref 10 and 19). 
COST ESTIMATE 
The cost of an operation to place a large quantity of concrete in 
the deep ocean can be roughly estimated and compared to that of a similar 
grouting operation. These costs can also be compared to a generalized 
estimate that would represent a major salvage operation. 
Material costs are less for concrete than for grout because less 
cement is used. Table 5 shows this comparison. For a job requiring 
10,000 cu yd, which would be a task equivalent to encasing a ship-sized 
object, the material cost is about $300,000 for concrete, $460,000 for a 
sand/cement grout and $630,000 for a neat cement grout. 
The unit weight of concrete is considerably greater than the unit 
weight of grout. Table 6 compares the total quantity of material for a 
task that requires a submerged weight of 25 million pounds which is 
beyond deep water lifting capability. A 25,000,000-l1b submerged weight 
could be provided by 10,000 cu yd of concrete or 15,000 cu yd of cement 
slurry. For this case, the material costs are $300,000 for concrete, 
$550,000 for a sand/cement grout, and $940,000 for a neat cement grout. 
Material costs are important; however, at-sea operational costs are 
more significant in controlling overall project costs. It is difficult 
to quantitatively define some of these costs but qualitatively they may 
be compared. For instance, the logistics of supplying materials to the 
surface platform is a major factor. A drill ship will carry about 850 
cu yd of cement. One cubic yard of cement makes 3.6 cu yd of concrete, 
1.8 cu yd of sand/cement grout or 1.2 cu yd of neat cement grout. An 
offshore resupply boat normally carries about 350 cu yd of cement but 
can be outfitted with portable tanks to carry up to 800 cu yd of cement. 
An aggregate barge towed by a tug will supply the aggregate. A barge of 
2,600 DWT capacity is assumed. Table 7 shows that fewer resupply trips 
are required to supply the cement and aggregate for concrete than to 
supply just cement or cement and sand for grout. Depending on the 
distance from land, fewer resupply trips can save tens to hundreds of 
thousands of dollars. 
Time on-site while placing the material will affect the overall 
cost because drill ships lease at about $30,000/day. It has been stated 
in a previous section that the flow rate for concrete was estimated at 
30 to 50 cu yd/hr using the method presented herein. For 10,000 cu yd, 
this equates to 8 to 14 days of continuous, round-the-clock operations. 
(This time could be shortened by using multiple pipes instead of just 
one pipe.) It is considered likely that the flow rate for grout would 
22 
