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The assignment of civil engineering contain these points:Required Average, Determine, Standard Deviation, Compressive Strength, Determine Water Cement Ratio, Strength, Interpolation, Determine Mixing Water Requirement, Air Content, Cement Content
Typology: Exercises
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(1) Determine Required Average Compressive Strength
Since the standard deviation of the compressive strength is known, f (^) cr = f’c + 1.34 S = 5200 + 1.34 (350) = 5669 psi f (^) cr = f’c + 2.33 S - 500 = 5200 + 2.33 (350) -500 = 5516 psi Use f (^) cr = 5700 psi (10 pt.)
(2) Determine Water Cement Ratio w/c for strength (Table 9-3) : .43 (by interpolation) (w/c = .41 at 6000 psi; w/c = .48 at 5000 psi) w/c for exposure (Tables 9-1, 9-2): N.A. Use w/c = 0.43 (10 pt.)
(3) Determine Mixing Water Requirement & Air Content Mixing water (Table 9-5): 340 lb / yd^3 (3-4 in. slump, non-air-entra., nom. max. agg. size: 3/4 in.) (5 pt.) Air content (Table 9-5): 2.0% (5 pt.)
(4) Calculate Required Cement Content
Cement based on w/c: 340/0.43 = 791 lb/yd^3 (10 pt.)
(5) Determine Coarse Aggregate Content
Dry-rodded volume (Table 9-4) 0.66 yd^3 /yd^3 (F.M. of sand = 2.4, Nom. Max. Size = 3/4 inch) Dry wt. of C.A.per yd^3 of concrete: 0.66 X 27 X 89 = 1586 lb. (10 pt.)
(6) Determine Fine Aggregate Content Absolute Volume of ingredients (per yd^3 ) Water 340/62.4 = 5.449 ft^3 Cement 791/(3.15X62.4) = 4.024 ft^3 C.A. 1586/(2.34X62.4) = 10.862 ft^3 Air 0.02 X 27 = 0.540 ft^3 Total = 20.875 ft 3 (10 pt.) Absolute Volume of Sand = 27 – 20.875 = 6.125 ft^3 Dry Wt. of sand = 6.125 X 2.62 X 62.4 = 1001 lb. (10 pt.)
(7) Adjustments for Agg. Moisture
Wt. of agg. In natural moisture condition: Coarse Agg.: 1586 X 1.025 = 1626 lb Fine Agg.: 1001 X 1.002 = 1003 lb (10 pt.)
Additional water needed by agg.:
Coarse Agg.: 1586 X (0.045 - 0.025) = 31.7 lb Fine Agg.: 1001 X (0.003 - 0.002) = 1.0 lb 33 lb Adjusted mixing water: 340 + 33 = 373 lb (10 pt.)
Summary of Mix Ingredients for 1 yd^3 of concrete Water 373 lb Cement 791 lb Coarse Agg. 1626 lb Fine Agg. 1003 lb 3793 lb (5 pt.)
Calculated Unit Wt.: 3793/27 = 140.5 pcf (5 pt.)