huangyhg

concrete mix
i am looking a set of structural drawings from 1918. the concrete mix is called out as 1:1:2 and 1:2:4. does anybody know what this means? what would be the corresponding strengths of concrete?
respectively, the figures refer to the amounts of cement, sand and stone or aggregate, in that order, by unit of measure (cu yd).
i looked in a 1919 edition of "trautwine", but could find no reference to the strength. i found only a general estimation formula, but nothing specific.
if you do not have a meter to determine the f'c, you might consider taking and testing two or three core samples.
mike mccann
mccann engineering
it's probably a 2000 psi mix; that was a common strength at the time. if you have the aashto condition evaluation of bridges or aashto maintenance manual, they might allow slightly higher. i'm out of the office today so i can't check until wednesday.
as mike said, consider a few cores if necessary. it's possible that they might come up higher than 2000 psi.
i am not an expert on concete mixes, but to me it sounds like the ratio of materials. cement: fine agg: coarse agg. i re
since these proportions are based on loose volumes, one can compute the approximate proportions for 1 cubic yard ssd mix based on certain assumptions.
for a 4 inch slump and about 36-38 gal of water/cu.yd...no admixture..sgs of cement and aggregate at 3.15 and 2.65 respectively, loose unit weights of cement and aggregate of 94 lb/cu.yd and 100-105 lb/cu.yd:
1. the 1:2:4 mix would approximate a 5scy mix with a w/c of about 0.67. i'd say that might work for a f'c of between 2000 to 2500 psi at 28 days. the in-situ concrete is much older now.
2. the 1:1:2 mix will be much richer in cement and have a mcuh lower w/c ratio than the 1:2:4 mix....less than 0.40. consequently the f'c requirement will be higher than the 1:2:4 mix. was this used for beams and columns?
all the same, i support the suggestion that cores be taken to evaluate strength.
aashto permits f'c of 2,500 psi for concrete in good condition, placed prior to 1959.
go to this website for the definitions:
that is the concrete composition satarting with cement, sand(fine aggregates) and coarse aggreagates. the corresponding strength are 30-45mpa(n/sq.mm) and 20-30mpa(n/sq.mm) respectively. those are just rough values as concrete strength depends on a lot of factors. mentioning a few, water to cement ratio(w/c), curing of concrete and compaction. im sorry, im very familiar with si units and not imperial units
i agree with florahaule. in volume batching 1:1:2 is grade 30 concrete (30 n/mm2) and 1:2:4 is grade 20 concrete (20 n/mm2) as i can remember water cement ratio is in the range of 0.5 - 0.55 to achieve this strength.
since the building is approx. 100 yrs old, my suggestion is to test some concrete cores. there can be deterioration due to carbonation etc.

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