The columns for a building in central Long Island are to be made of concrete with...

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Civil Engineering

The columns for a building in central Long Island are to be madeof concrete with the
following specifications:
• Design compressive strength: 4500 psi, based on 20 tests ofsamples having a
standard deviation of 600 psi
• Non-air entrained, and clear space between rebar: 1.5 inch
• Fine aggregate: G = 2.350, FM = 2.5
• Coarse aggregate: G = 2.65, bulk density = 3000 lb/cy

Determine the following:
i. w/c ratio, largest nominal max. coarse aggregate size, % coarseaggregate, % air
(2 pts.)
ii. weight of water, weight of cement, and weight of coarseaggregate to be used per
cubic yard of concrete (1 pt.)
iii. weights and volumes of water, cement, air, coarse aggregate,and fine aggregate
needed to mix a 15-yard batch of this mix (3 pts.)
Also:
• Specify two admixtures that might be used for this mix based onthe provided
information, and why to use it. (2 pts.)
• Why we might create a composite of this concrete poured into aPVC (polyvinyl
chloride) sleeve for these columns? (Give specific reasons based onthe
characteristics of the individual materials.) (2 pts.)

Answer & Explanation Solved by verified expert

3.8 Ratings (455 Votes)

Ans i According to ACI 318 when number of samples tested isless than 30 a modification factor is needed to multiplied bystandard deviation to obtain adjusted standard deviationAccording to Table 11 ACI 318 for number of test 20modification factor is 108 Adjusted standard deviation s 108 x 600 648 psiAccording to table 12 ACI 318 for strength 5000 psi required compressive strength fcr is larger of fcr fc 134 sorfc 233 s 500Hence fcr 4500 134648 5368 psiorfcr 4500 233648 500 5510 psi fcr 5510 See Answer

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