Circular prestressed concrete tanks have been in various stages of development and renovation for decades. Early systems used in the United States called for the employment 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 the placement of the concrete, together with insufficient residual compression in the core wall, brought about modifications and upgrades.
In the early 1930s, 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. This system incorporated a steel shell cylinder with shotcrete encasement for the core wall and high strength wire for the prestressing elements.
Prestressed Concrete Tank Construction
Over the years, successors to Mr. Crom have improved and perfected the composite system for tank wall construction. These improvements have included the selection of better construction materials as well as ever-improving design and construction procedures. Consideration was given to:
- 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.
The development of the prestressed composite system emerged from these considerations as the most effective and enduring approach to circular prestressed concrete tanks. The composite system includes such proven tank engineering truths as:
- The steel shell diaphragm has been found to be the most foolproof means for making the core wall watertight.
- Shotcrete with its high cement factor and low water to cement ratio has greater corrosion inhibition, impermeability, and strength than conventional concrete.
- High-strength wire can be used to more accurately apply prestressing forces and could be better protected from corrosion and mechanical damage.
In the early 1950s, J.M. Crom, Sr., and three associates, Ted Crom, Jack Crom, Jr., and Frank Bertie, established CROM, with headquarters in Gainesville, Florida. The prime purpose of the company was to refine the design and construction techniques of composite tanks. Since then, the subsequent leadership and employees of CROM have continued the tradition of excellence initiated by the company’s founders. To date, the company has constructed, in its own name and with its own forces, over 4,100 circular and elongated prestressed concrete tanks.