Design the concrete mix according to the following conditions: design environment building frame required design strength -27.6 mpa minimum dimension-150 mm minimum space between rebar minimum cover over rebar 40 mm statistical data indicate a standard deviation of compressive strength of 40 mm 2.1 mpa is expected (more than 30 samples) only air entrainer is allowed available materials air entrainer: manufacture specification 6.3 ml/100 air/100 kg cement. coarse aggregate: 19 mm nominal maximum size, river gravel (rounded) bulk oven-dry specific gravity-2.55. absorption-0.3% oven-dry rodded density - 1761 kg/m3 moisture content 2.5% fine aggregate: natural sand bulk oven-dry specific gravity-2.659, absorption-0.5% moisture content-2% fineness modulus 2.47