Circular prestressed concrete tanks have been in various stages of development and perfecting for decades. Early systems used in the United States called for the use of cast-in-place concrete in the core
wall of the tank and steel rods with turnbuckles as the prestressing elements. Although theoretically this approach to circumferentially prestressed concrete tanks was sound, deficiencies in placement of
concrete together with insufficient residual compression in the core wall brought about modifications and improvements.
In the early 1930's, the matter was fully understood when J.M. Crom, Sr. began the development of what was later to become the COMPOSITE system of tank wall construction, using a steel shell cylinder with shotcrete encasement for the core wall, and high strength wire for the prestressing elements.
Successors to Mr. Crom have over the years improved and perfected the COMPOSITE system for tank wall construction. These improvements have included the selection of better construction
materials, together with ever-improving design and construction procedures. Consideration was given to:
Emerging from all of these was the development of the prestressed
- Ready-mixed concrete and pneumatically applied shotcrete in combination with a steel shell diaphragm.
- Prestressing rods, cables and high-strength wire.
- Emulsion type sealants, polysulphides, polyurethanes, and epoxies for sealing the steel shell membrane.
- Wall base joints using conventional waterstops; special bearing pad and waterstop combinations; and monolithic floor-wall joint connections.
In the early 1950's, J.M. Crom, Sr. and three associates, Ted Crom, Jack Crom, Jr., and Frank Bertie, established The Crom Corporation, with headquarters in Gainesville, Florida, for the prime purpose of perfecting the design and construction techniques for COMPOSITE tanks. Since then, their successors have continued the tradition of excellence initiated by the company's founders. The company has constructed in its own name and with its own forces over 3,300 circular and elongated prestressed COMPOSITE tanks.
- The steel shell diaphragm was found to be the most foolproof means for making the core wall watertight.
- Shotcrete with its high cement factor and low water/cement ratio had greater corrosion inhibition, impermeability and strength than conventional concrete.
- High-strength wire could be used to more accurately apply prestressing forces and could be better protected from corrosion and mechanical damage.