Comparison of strength and construction tolerances in concrete

Two approaches to the tolerance limit for compressive strength of concrete in reinforced members are compared. One tolerance limit for strength, in use since 1971, is f'c - 500 psi (3.4 MPa). Another tolerance, based on 0.90 f'(c), provides a more direct link between design and quality control criteria consistent with the use of strength reduction factors. The utility of each tolerance was evaluated by comparing the effect of the tolerance on selected structural capacities with the effects of other typical construction tolerances. On this basis, the investigation Sound that a strength tolerance of 0.90 f'(c) is a more consistent representation of allowable concrete strength variation than f'(c) - 500 psi (3.4 MPa). While this approach is not sufficient by itself; it does indicate that the 0.90f'(c) criteria is a more rational approach to compressive strength tolerance.