Presents an analysis of the influence of specimen size on the measured
compressive strengths of plain and fly ash concretes exposed to stand
ard and cold-curing. Strength tests were performed on three classes of
air-entrained concrete using two subbituminous fly ashes at three rep
lacement levels. Analysis of the present experimental results, combine
d with other results presented in the literature, shows that the compr
essive strength indicated by 75-mm (is-approximately-equal-to 3-in.) c
ylinders is statistically identical to that indicated by 150-mm (is-ap
proximately-equal-to 6-in.) cylinders. Analysis suggests that this one
-to-one relationship between strength of 75- and 150-mm cylinders may
be valid for concrete strengths up to 50 MPa (7250 psi). Further analy
sis of published data leads to the conclusion that the equality of str
ength among specimen sizes also includes 100-mm diameter cylinders. Th
e type of mold used to cast test cylinders, whether cardboard, steel,
or tin, does not have a significant effect on the trends observed.