Building Materials, Third Edition

g™

2w2h QQU

Free water in fine aggregate

= 537.39 2
2 10.75 lit
100
Therefore, actual quantity of water required
= 188.8 + 5.98 – 10.75 = 184.03 lit.
Actual quantity of coarse aggregate = 1195 – 5.98 = 1189.02
and sand = 537.39 + 10.75 = 548.14
Therefore, the actual quantities of materials required are:
Cement Water Sand Coarse
472 kg 184.03 lit 548.14 kg 1189.02 kg.
Step 6: The fraction I and II of the coarse aggregates are to be now combined to give a
combined grading in accordance with IS:383–1970 of 20 mm maximum size aggregate. To
obtain a combined grading, IS: 383–1970 recommends that the fraction passing the 10 mm sieve
shall be in the range of 25 to 55 per cent, or on an average of 40 per cent. Trials are then made
to combine the fraction I and II in the proportion of, say 40:60 to see whether the combined
grading is obtained. This is given below.

s   2   5 p—™2sD p—™2ssD g˜ h   2—

  — IH22wƒeD PH22wƒeD — PHE2wƒeD

RH22™ TH22™ —   22sƒX2QVQ

RHE-- RH TH IHH IHH

PSE-- RH TH IHH IHH

PHE-- RH SSP 22WSP WS22IHH

IPSE-- RH IS 22SS E

IHE-- QSP 22VR 22RQT PS22SS

RUSE-- 2222RV 22IV 2222ST H22IH

PQTE-- 2222IP 22' 2222IP E

It can be observed that if the fractions I and II are combined in the ratio of 40:60 the desired
combined grading as recommended in IS:383–1970 is obtained. The mix proportions for the
trial mix will now be

g ‡— ƒ— g— 2—™2s e—
IH22wƒe —™2ss
PH22wƒe

RUP IVRHQ SQUQW RUST UIQRI
D2I HQWI IIQV IHHU ISI

iˆi‚gsƒiƒ

1. Define concrete mix design and state the principle of mix design.


2. Concrete mix design is still very much a problem of trial and error. Comment!


3. What are the various grades of light and medium concrete? What information is required
   for mix design from the site of the work?