Design the concrete mix proportion for a structure that will be below ground level in a location where it will not be exposed to severe weathering or sulfate attack. Structural considerations require it to have an average $28-$day compressive strength of $24$ MPa with slump of $75$ mm The coarse aggregate has a nominal maximum size of $20$mm and dry$-$rodded mass of $1600$ kg$/$m$3\mathrm{.}20$mmOther properties of the ingredients are: Cement: Type I with specific gravity of $3\mathrm{.}15$Moistur constant Coarse aggregate: Bulk specific gravity $=2\mathrm{.}68,$ Absorption $=0\mathrm{.}5\%$Moisture constant $=0\mathrm{.}2\%$ Fine aggregate: Bulk specific gravity $=2\mathrm{.}64,$ Absorption $=0\mathrm{.}7\%,$Fineness modulus $=2\mathrm{.}8.$and Moisture content $=0\mathrm{.}1\%$Find the fcr$\text{'}$ using ACI $3/8$ The number of spa$-$cement $45$ and the standard deviation S$=4$MPa