4. Design the concrete mix according to the following conditions: Design requirements: su -Water structure with mild sulfate exposure in freezing climate -Required design strength = 40 Mpa -Minimum dimension = 150mm -Minimum space between rebar = 50mm -Minimum cover over rebar = 40mm -Statistical data indicates a standard deviation of compressive strength of 2.5 Mpa is expected (25 samples) -Only air entertainer is allowed Available material -Air entertainer is 4.5 ml/1%air/100 lb cement -Course aggregate: 19mm maximum size, river gravel (rounded) -Bulk oven-dry rodded density = 2.55, absorption = 0.25% -Oven-dry rodded density = 1761 kg/m3 -Moisture content = 2.5% -Fine aggregate: Natural sand -Bulk oven dry specific gravity = 2.65, absorption = 2% -Moisture content = 0.9% -Fineness modulus = 2.52