concrete mix

[broncosfan]

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?

 

[msquared48]

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

 

[bridgebuster]

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.

 

[DWHA]

I am not an expert on concete mixes, but to me it sounds like the ratio of materials. Cement: Fine Agg: Coarse Agg. I remember back in college our materials teacher said a good standard mix to start a design with is 1:2:3, and the materials are always listed from finest to the most coarse.

 

[henri2]

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.

 

[bridgebuster]

AASHTO permits f'c of 2,500 psi for concrete in good condition, placed prior to 1959.

 

[philgirv]

Go to this website for the definitions:

http://www.deeconcrete.com/concreteglossaryc.html#cement_mixture

based on my fathers old british Reinforced concrete Designer's handbook, 1:1:2 concrete is typically high strength for it's time and is between 4000 to 4500psi.
1:2:4 concrete is standard concrete at 3000psi.

 

[GoddyMgwasa]

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

 

[KCRatnayake]

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.