Does aggregate make higher or lower F'c
Does aggregate make higher or lower F'c
(OP)
I've had some time to purge random thoughts about the business, and had noticed that grout (sand only) has significantly higher F'c than concrete. Is this just because of the higher cement content? Does aggregate just fill up space without significantly detracting from the compressive strength? Does it add strength? Just a thought in passing.
PS. I live in the Pacific Northwest, so we're talking durable gravels, not pumice or lightweight. Or that too, if you're interested.
PS. I live in the Pacific Northwest, so we're talking durable gravels, not pumice or lightweight. Or that too, if you're interested.





RE: Does aggregate make higher or lower F'c
RE: Does aggregate make higher or lower F'c
RE: Does aggregate make higher or lower F'c
Site cast concrete cylinders are cast in non-absorbant molds to match the procedure and are used as a comparison of the mix materials to the original mix design. They are cured in under laboratory conditions. They are not intended to accurately reflect the actual strength (f'c) of the concrete in place, since this is a affected by the result of the mix, placement and curing.
If you are refering to masonry grout (f'g), the samples are cubes cast in an absorbant "mold" consisting of the units used in the project. The purpose of the test is to provide a measure of the actual grout in place where the units absorb the excess moisture required to place the 8-11" slump grout. Normally, high strength masonry grouts are not necessarily an asset in the structure, because they can provide a misleading measurement of the structure's strength. The controlling strength measuerment for masonry is the prism strength (f'm).
Other types of grout such as non-shrink and grout for anchoring embedment and other uses have different properties and requirements and the test/sampling procedures are not at all similar to concrete cylinders.
You cannot compare apples and oranges since the desired properties, placement and testing procedures are different. Even in some types of cement-based materials, the addition of water will provide more strength than cement on a weight basis.
Dick
RE: Does aggregate make higher or lower F'c
you have to convert cube strength for an equivalent cylinder strength.
RE: Does aggregate make higher or lower F'c
RE: Does aggregate make higher or lower F'c
RE: Does aggregate make higher or lower F'c
Masonry grout has two different sizes (fine and coarse) that are controlled by the use. In many cases, 3/8" aggregate would not be acceptable and would be detrimental to construction. Masonry grout has an absolute maximum allowable strength of 5000 psi according to ASTM C476 and normally 2000-3000 psi is specified and preferred. You do not want larger size aggregate in a grout and you are not after high stregths - its the old story of stronger not being better.
Larger aggreagate will give higher strengths with all other things equal. The problem is that large aggregate may be detrimental to the application or may not comply with the specifications. In most situations, not all thing are or cannot be equal.
Dick
RE: Does aggregate make higher or lower F'c
RE: Does aggregate make higher or lower F'c
RE: Does aggregate make higher or lower F'c
RE: Does aggregate make higher or lower F'c
The only real problem with grout is not the proportioning and strength variations, but the rate of placement and lack of reconsolidation.
Too often, construction masterials get lumped together just because of the raw materials, while the desired properties design requirements and placement methods that really produce quality construction are more important. Combining plant produced products with site created reults takes good engineering and an understanding of the properties and advantages/disadvantages.
RE: Does aggregate make higher or lower F'c
RE: Does aggregate make higher or lower F'c
Your university learned definitions for mortar and concrete are still correct, although there are often other things added to improve some property or other.
Grout is the one with lots of meanings. When grouting posttensioning tendons, you use cement and water (and sometimes an admixture). When grouting under a steel column base plate, you use cement, fine aggregate, and water (and in the case of premixed grout, who knows what else). When grouting concrete blocks, you use cement, fine aggregate, generally a rounded small but coarse aggregate, water, and again probably admixtures. I think the reason for calling this particular type of concrete "grout" is that it is used to fill confined spaces.
RE: Does aggregate make higher or lower F'c
At the same water-cementitious materials ratio, there is an inverse relationship between MSA and f'c. This is why smaller nominal max aggregate mixes are used for high strength concrete (6000 psi and greater).
ACI materials journal has several papers which focus on this issue...but I think you have to be a member to download their papers. Google scholar is another source.
RE: Does aggregate make higher or lower F'c
In school you should have performed some testing on concrete cylinders. In early age concrete, the paste debonds from the face of the coarse aggregates. But once the paste has gained adequate strength, the aggregates fracture and a good test will show an abundance of fractured aggregates.
I am not well versed in masonry and grout.
RE: Does aggregate make higher or lower F'c
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RE: Does aggregate make higher or lower F'c