than by tremie. Specially designed bucket methods have been proposed 
that would be suitable for placing small but not large quantities of 
concrete in the deep ocean (Ref 7 and 8). 
Concrete Pumping. Pumping concrete through pipelines of 2-in. to 
8-in. diameter is a well-established practice on land for horizontal 
distances of 1,000 ft or greater and vertical distances of several 
hundred feet upward (Ref 10). Reliable equipment and experienced oper- 
ators are available; mix design is well known to produce pumpable, good 
quality concrete. Difficulties that do occur are usually due to not 
following standard procedures, for example, attempting to save costs by 
using borderline materials, equipment or practices, or are due to opera- 
tional delays. 
Pumping downhill is often troublesome and is not frequently done. 
However, in some instances, concrete has been pumped down for placement 
underwater in water depths to about 200 feet. In pumping downhill it is 
important to avoid the formation of air pockets and voids in the pipeline. 
Both large air bubbles and voids can disrupt the flow and cause segregation 
of the mix which in turn causes blockage of the pipeline. A bleed valve 
at the high point of the pipeline is used to vent air during initial 
filling of the pipe with concrete, after which the valve is closed. 
Flow is then maintained under continuous positive pressure to prevent 
formation of voids. 
Pumping methods offer the potential for an order-of-magnitude 
increase in water depths at which concrete can be placed provided that: 
(1) means are developed to maintain a positive pressure continuously 
throughout the fully-filled pipe and to control the flow rate, and (2) 
the characteristics of the fresh concrete required for the controlled 
flow in the pipeline can be made compatible with the concrete character- 
istics required after the concrete is discharged from the pipe at the 
seafloor. The placement method discussed in this report uses a closed 
system, pumping approach. 
Pumping Grouts and Mortars. Grout is a mixture of either cement 
and water (neat cement grout) or cement, water, and sand (sand grout), 
both having a fluid consistency. Mortar is a mixture of cement, water, 
and sand usually of a stiffer consistency than grout. Grouts and mortars 
often contain admixtures to control setting, minimize bleeding, or 
otherwise affect the material characteristics. Grouts and many mortars 
are readily pumped. 
Grouts are regularly pumped through small (e.g., l-in.) diameter 
pipes and placed in confined spaces for many construction applications, 
such as repair of concrete, encasement of post-tensioning tendons, and 
construction of water cut-off curtains under dams. 
Grout pumping is also used for underwater concreting by the pre- 
placed aggregate method by which large quantities of concrete have been 
successfully placed to depths greater than 100 feet for construction of 
large bridge piers and other purposes. The coarse aggregate is placed 
in forms and then intruded with a fluid grout through pre-positioned 
grout pipes. This method might be adapted to deep ocean placement but 
probably would require a complex operation since separate placement 
