(2) A SCC concrete mixture has a proportion of 1:0.4:2:2 (B:W:S:A). In the binde
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Question
(2) A SCC concrete mixture has a proportion of 1:0.4:2:2 (B:W:S:A). In the binder content, 60% is Portland cement, 25% is fly ash (FA), and 15% is GGBS. The concrete also uses 2% superplasticizer (solid content to cement ratio). The absorption for sand is 1.5% and for aggregate is 0.8%. The MC (OD) is 2.5% for sand and 1% for coarse aggregate. The solid content of superplasticizer is 30%. To cast 3 cubes (500 x 500 x 500 mm), how much of each individual ingredient should be used (consider 7.5% extra amount)? (25)Explanation / Answer
Step 1:
Given data:
Mix proportion=1:0.4:2:2
Binder=OPC(60%)+fly ash(25%)+GGBS(15%)
Super plasticizer=2% (Solid content to cement ratio)
Absorption of sand=1.5%
Absorption for aggregate=0.8%
Moisture content=2.5% for sand
Moisture content =1% for Coarse aggregate
Solid content of super plasticizer=30%
step 2:
Calculate the total volume of concrete specimen:
Volume of each cube=0.5x0.5x0.5=0.125m3
Step 3:
Total weight of concrete =
0.125x2400x(1+0.75)=322.5 kg (since we require 7.5% extra)
step 4:
Calculation of cement, fly ash and GGBS
Weight of Binder=322.5 kg/(1+0.4+2+2+0.02)
Weight of Binder=59.5 kg
Weight of OPC=59.5x0.6=35.7 kg
Weight of fly ash=59.5x0.25=14.875 kg
Weight of GGBS=59.5x0.15=8.925 kg
Step 5:
For sand:
Weight=2x35.7=71.4 kg (Note that here the content is based on cement and not on binder)
Wstock=W[(1+MC(OD))/(1+ABSORPTION)]
Wstock=71.4[(1+0.025)/(1+0.15)]
Wstock=63.63 Kg
Water provided by sand=71.4-63.63=7.77 kg
Step 6:
For Aggregate
Weight=2x35.7=71.4 kg (Note that here the content is based on cement and not on binder)
Wstock=W[(1+MC(OD))/(1+ABSORPTION)]
Wstock=71.4[(1+0.01)/(1+0.0008)]
Wstock=72.05kg
Water provided by Aggregate=71.4-72.05= -0.65 kg
Step 7:
For super plasticizer,
W=0.02x35.7=0.714 kg
As the solid content is 30%
Weight=0.714/0.3=2.38 Kg
Step 8:
For water:
0.4x35.71-(7.77-0.65+2.38)
=4.784 Kg
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