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: â€¢ Design compressivestrength: 4500 psi, based on 20 tests of samples having a standarddeviation of 600 psi â€¢ Non-air entrained, and clear space betweenrebar: 1.5 inch â€¢ Fine aggregate: G = 2.350, FM = 2.5 â€¢ Coarseaggregate: G = 2.65, bulk density = 3000 lb/cy Determine thefollowing: i. w/c ratio, largest nominal max. coarse aggregatesize, % coarse aggregate, % air (2 pts.) ii. weight of water,weight of cement, and weight of coarse aggregate to be used percubic yard of concrete (1 pt.) iii. weights and volumes of water,cement, air, coarse aggregate, and fine aggregate needed to mix a15-yard batch of this mix (3 pts.) Also: â€¢ Specify two admixturesthat might be used for this mix based on the provided information,and why to use it. (2 pts.) â€¢ Why we might create a composite ofthis concrete poured into a PVC (polyvinyl chloride) sleeve forthese columns? (Give specific reasons based on the characteristicsof the individual materials.) (2 pts.)

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3.8 Ratings (430 Votes)

Ans i According to ACI 318 when number ofsamples tested is less than 30 a modification factor is needed tomultiplied by standard deviation to obtain adjusted standarddeviationAccording 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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