An important step toward achieving control of concrete uniformity was taken in 1971 with the acceptance of a major revision of the American Concrete Institute's Building Code Requirements for Reinforced Concrete, which is usually referred to as ACI 318. ACI 318 is a long, complex standard that deals with structural design as well as quality control of concrete materials. The changes in structural design provisions result in reduced cross-sections of structural members, and more efficient, economical design in concrete construction. This, of course, means that it is more important than ever that concrete uniformly develops specified strength.
According to ACI 318 requirements, if a producer's standard deviation exceeds 600 psi or if he cannot (or chooses not to) furnish records of the standard deviation he has achieved on previous jobs he must select mix proportions such that the strength will exceed that specified by 1200 psi.
ACI 318 encourages production of more uniform concrete, bidding based on comparable concretes, economy in keeping with quality and an upgrading of production control. A performance specification like ACI 318 offers important advantages to all members of the building team. For the concrete producer, it means equalized competition. The specifier takes a reduced risk he knows that he has a better chance of getting concrete from a quality-conscious producer and therefore he faces fewer problems on the job. He has recognized acceptance standards an enforceable way of controlling concrete quality. The contractor benefits from concrete that more uniformly develops the strength he needs, and also is likely to be more consistent in plastic properties. This means fewer job delays faster erection, enclosing and occupancy of a building. It also means lower costs for the contractor and a happier owner, who can rest assured that he is getting uniform quality concrete at the lowest price.