Answer to Question #311907 in Civil and Environmental Engineering for Oxian

Question

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 = 40 mm

Minimum cover over rebar = 40 mm

Maximum slump is required

Statistical data indicate a standard deviation of compressive strength of 2.1 MPa is

expected (more than 30 samples).

Only air entrainer is allowed.

Available Materials

Air entrainer: Manufacture specification 6.3 ml/1% air/100 kg cement. (Use maximum

or +2% air content)

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%

Fine aggregate: Natural Sand

Bulk oven-dry specific gravity = 2.6

Answer 1

OR BUILDING SLUMP IS 25-100

FOR 19MM AGGREGATE SIZE

WATER REQUIRED IS 168KG/CUM

FOR STRENGTH OF CONCRETE =27.6

CORRESPONDING WATER CEMENT RATIO IS 0.48

WATER=168

Cement required =168/(0.4)=247kg/cum

for fineness of =2.47

and for aggregates size=19mm

Aggregate required =0.65 cum

density of AGGREGATE =1761

wt of aggregates =0.65$\times$ ×1761=1144kg/cum

wt of cement =247

wt of water =168

wt of aggregates =1144

density of water =1000kg/cum

vol of water =0.168 cum

density of cement =1400kg/cum

vol of cement =0.176

vol of AGGREGATE =0.65

vol of water=0.168

vol of cement =0.176

due to moisture and absorption 

reduce volume 

volume =0.63

vol of water =0.15

vol of cement =0.16

vol of fine =1-0.63-0.15-0.16=0.06 cum

vol of agg=0.63

vol of fine =0.06

vol of water =0.15

vol of cement =0.16

wt of aggregates =0.63×1761

=1109kg

wt of water =150 kg

wt of cement =210 kg

wt of fine =2.659×1000×0.06=159.6 kg

These are required for 1 cum of concrete