Problem 4. Concrete mix design Problem (60 points) The specific compressive stre

Question

Problem 4. Concrete mix design Problem (60 points) The specific compressive strength (or design strength) of concrete, fc'-3500 psi. The concrete is used for casting 4 ½ inch thick slab and the spacing between reinforcement bars in the slab will not less than 12 inch. Type I cement will be used for mixing concrete (Fill answer in following blank) What is the slump required for the concrete? (5 points) 1. 2. What is the maximum size of coarse aggregate that can be used for the concrete? (5 points) 3. If the slab is supposed to be exposed to environment, should be non-air-entrained concrete with 1% air content or air-entrained concrete with air content of 5% selected for the project? (5 points) 4. What is the amount of water in lbs. should be used for mixing I cubic yard (5 points) 5. What is the maximum permissible water/cement ratio (w/c) that can be used for (5 points) concrete? mixing concrete? The specific gravity of coarse aggregate, SGca 2.69. The specific gravity of fine aggregate, SGa 2.65. The specific gravity of cement, SG.ce-3.15. Bulk density of dry- rodded of coarse aggregate, Bca 105 pcf. Water density, Dwa 62.4 pcf. 6. Determine the amount of coarse aggregate in lbs that is needed for mixing I cubic yard concrete (show calculation procedures) (10 points) 7. Determine the amount of fine aggregate in lbs that is needed for mixing I cubic yard concrete (show calculation procedures) (10 points) Instructor: Wei Zheng

Explanation / Answer

1. As per ACI code the recommended maximum slump for concrete used for slab construction is 3 inch.

Answer 3 inch.

2. As per ACI code the maximum aggregate size should not be larger than -

   1/3 the thickness of slab = 1/3 x 4.5" = 1.5 inch

Answer maximum size of coarse aggregate = 1.5"

3. Since the slab is exposed to environment it should be air entrained concrete with with air content of 5%.

Answer - air entrained concrete with with air content of 5%.

4. As per ACI code for air entrained concrete with slump between 3 to 4 inch and 1.5 inch aggregate size the apporximate mixing water required is 275 lb/yd3

Answer - 275 lb/yd3

5.The maximum permissible water/cement ratio for compressive strength of 3500 psi and Air-entrained concrete is 0.54

Answer maximum water/cement ratio = 0.54

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