1.25" vs 1" aggregate for concret mix 1

[delagina]

I'm looking for a good reference about concrete mix. As a starter I want to know the effect of using 1.25" aggregate as opposed to 1". Also other stuff like pro and con of using limestone, river rock, different admixtures, air entrain percent etc..

 

[dik]

The difference between 1.25 and 1 inch aggregate is negligible. There would be a very slight difference in shrinkage and also a marginal improvement in shear capacity.

Regarding your other issues, the question is too 'big' and could fill volumes. You should not use rounded aggregate for concrete.

Dik

 

[JedClampett]

PCA's "Design and Control of Concrete Mixes" is pretty good. I've attached what they said about aggregate size in 1968.

 

[dik]

Jed:

The difference between 1 and 1-1/4 aggregate is only a matter of maybe 10 pounds of water per yard, hence, the slight reduction in shrinkage. My copy of 'Design and Control of Concrete Mixes' is of that vintage... a little 'dog eared' but still legible. Haven't looked at it lately (maybe 30 years), but, at the time is was an excellent source of information. As you note, it still is... one of those publications that seems to be timeless.

I should have added that with the Canadian Concrete code, there is a significant difference in shear strength if you use 19mm or 20mm for your max aggregate size... the cut-off is at 20mm... and 3/4" (19mm) technically does't make the grade.
Dik

 

[Ron]

In general, the larger the aggregate, the lower the cement content needs to be...all other parameters being equal. This is the reason that shrinkage is lower for larger aggregates. The reason for this is the specific surface area of the aggregate that must be covered with cement paste to provide interstitial bond between aggregate particles is lower for larger aggregate.

The most prominent source of information on concrete is Adam Neville's various editions of his concrete texts. Any one of these will give you a good background in concrete. Other good references are the ACI Manual of Practice (expensive), but particularly ACI 211 which can be purchased as a separate standard. As JedClampett noted, PCA's Design and Control of Concrete Mixtures is a good source as well. I have several editions of this manual over the past 40 years and they keep up well with concrete technology.

Good concrete can be made with limestone (limerock), river rock and others, provided they are crushed stone, not rounded as dik noted.

Good concrete is made from cement, water and quality aggregates. Bad concrete is made from the same materials. It depends on how you design the mix, produce the mix, place and cure the concrete.

 

[dik]

Thanks Ron... I was commenting based on the diagram in Jed's posting. We know that larger aggregate displaces 'paste', hence, shrinkage. My comment was predicated on the diagram and on maintaining the same w:c ratio. The reduction in water would necessarily reduce the cement content, hence, shrinkage.

Dik