$7\mathrm{.}4.$ You are task with designing a concrete mix for a ploject with the following conditions and constraints:

Bridge caissons $($exposed to salt water and server sulfate exposure$)$

Design strength $f_c=3,500$

Standard deviation of fc obtained from $32$ samples$=350$psi

Thickness$=12"$

Cover over and between rebar is $2\mathrm{.}5"$

Use air$-$entrained concrete with admixture of $6\mathrm{.}3$flo$\frac{z}{1}\%$ air$/1001$b cement.

Fine Agg. Data

Fineness modulus of fine aggregate $=2\mathrm{.}60$

Natural Sand

Specific Gravity: $2\mathrm{.}572$

Absorption $=0\mathrm{.}8\%$

Moisture Content $=4\%$

Coarse Agg Data

Bulk oven$-$dry specific gravity of coarse aggregate $=2\mathrm{.}621$

Oven$-$dry rodded density of coarse aggregate $=105$ pcf

Absorption: $2\mathrm{.}4\%$

Moisture Content $=1\mathrm{.}5\%$