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Heading: 1.1.4.3.2.1.1.1Aggregate Fines
Message:
Incorporation of aggregate crusher fines in concrete seems to us like a green practice because using a material that might otherwise become waste is good for the environment; however, we understand that this idea may not earn green points or that no one has tried to earn points before. Does anyone have experience with this issue or know where to find more information please ?
thanks


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Margaret Reed


Lots of work has been done on this. Check out http://www.engr.utexas.edu/icar/publications/index.cfm. The problem is that the crusher fines have a higher water demand, which increases shrinkage and cracking and reduces strength. You may be able to use a cheap aggregate but the ultimate concrete cost will be much higher because of the need for additional cement.

I am having to do this in Zambia, where there is no good sand. We are using 742 lbs of cement/cyd to get an average strength of 7000 psi. And that is with using a lot of superplasticizer.

Jay Shilstone
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Jay Shilstone


Good idea to use crusher fines and if it is done well, it will be the concrete producer who will get your green points since he has a chance to use less "cement".
I disagree that more fines means automatically more water (and consequently more cement). Initially it might but if you increase fines correctly, water demand can well decrease. It all depends on the particle size distribution of ALL the fines (lets say under 125 µ). New milling techniques of cement has increased the water demand due to steep curved PSD. This can be compensated by other attractive fines such as calcium carbonate fines (CCF) on the lower end of the cement and fly ash and fine sands on the upper end.
Have a special lab, cement or CCF producer look at ALL the fines, especially yours!

The introduction in the Netherlands of the French concrete culture to use more fines to increase performance has been a great success. It means reducing portland cement while increasing strength and lowering the carbon footprint. We have two big aggregate suppliers here with great success stories on this with many customers.
Jay, what is your definition of "cement"? Do you consider composite cements and/or seperate added SCM's also cement?
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Boudewijn Piscaer


Could you provide additional information on the incorporation of aggregate fines in concrete in the Netherlands and France? Are there research documents or case studies that could help aggregate producers introduce this to hesitant concrete producers? Any information would be helpful. Thanks in advance.
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Adam Holst


Adam,

Sorry, previous reply interrupted by the need to run (or as near as I get to running these days) for a flight. What I meant to say was that manufactured sand varies widely in quality for use in concrete, depending on how it has been produced, and that goes for the microfines as well as the larger particles. Indeed, badly-shaped microfines will have a greater detriment to the performance of the sand due to the relatively large specific surface, or at least, that is what I understand from our experience. Furthermore, there seems to b a point somewhat smaller than the 75micron level at which crusher fines begin to cause excessive cohesion.

Regarding persuasion of reluctant users, I think the best way is to let them have bulk samples of the proposed manufactured sand, perhaps with varying levels of microfines, and the optimum material should sell itself.

For information on suitable manufacturing processes, please feel free to contact me at hugo_pettingell@hotmail.com

Hugo
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Hugo Pettingell


Guys

I have always felt that we need to distinguise the manufactured sand in by-product sand and manufactured sand. The by product sand is the sand that is made when you crush 4 to 5" rock down to 1-1/2 or 1" rock. This sand will have bad particle shape and will have a volume of # 4 x # 8 mesh. The manufactured sand made from a dedicated circuit where the crusher is set at 1/2" and the 1/2 x # 6 mesh is reciculated through the crusher and reduced by multilayer crushing (autogenous crushing) this will produce sand with as good a particle shape as a VSI rock on rock machine.

The next area is to stick to spec and guidelines of the ASTM C-33. the main ingredents of this spec is 95 to 100 % passing 4.7 mm, .187" or 4 mesh. 80 to 100 % passing 2 mm, ,093" or 8 mesh , 0 to 5 % passing .073 mm, .0029 or 200 mesh and finally a FM of 2.52 to 2.92. This will resolve most of the water, finishability and tecture issues.

To keep the manufactured fines gradation between 80 to 100 % passing 8 mesh the product top size is normally screened at mm, .131 or 6 mesh. Some cases where the rock is extremly hard and fine grained the top size of 8 mesh to reach the FM of less then 2.92.

To keep the minus 200 mesh to less then 5 % the sand has to be washed or air sperated since the normal hard rock will generate 10 to 15 % minus 200 with a cone and 15 -20 % using a VSI. In limestone the number will 1.5 times greater.

With the HP-4 and HP-5 cone crushers the crushing hold down forces have been increased to 1.5 times of the HP400 and HP500 respectively. This helps make the HP-4 crusher capabile of producing 6 mesh x 0 from 1" x 1/4 Rock at about 70 to 80 tph.

John Googins
Applications Engineer
Metso Minerals
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John Googins


John, some points about your response.

1. F.M. range, this is irrelevant to the performance of manufactured sand in concrete. Check out ICAR 102 Manufactured Sands for Concrete, the least correlation to any parameter measured in concrete performance was FM. Also, an FM value can yield many different grading curves. The speed of the VSI had more correlation than FM!

2. Autogenous crushing in a cone crusher is stretching reality a little far, sure, you may get some, but please be objective

3. High water demand is probably confused with high admixture demand – you need to figure out which is the dominant driver

4. Mineralogy of the manufactured sand has a massive impact on it’s suitability for concrete, and admixture demand

5. Particle packing in the minus 100 micron fraction also has a massive bearing on performance

6. Also, what about surface energy, and the change in surface energy over time?

7. Is the cement compatible with the admixtures, and, are the admixtures compatible with aggregates?

Be honest, crusher manufacturers do not have the expertise to tell you how a material will perform in it’s desired application. They can estimate the grading of materials produced, but this is only a small piece of the manufactured sand for concrete puzzle, and by far from the dominant force in determining value – just ask a concrete producer!

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Grant Gardner


Hi Guys,

Jay's problem in Zambia illustrates the problem of optimized mix design, namely that supply of the ideal blend of fines, sands, aggregates and even water is very often simply unavailable. His problem in the Zambia scenario would have easily been dealt with by using an additive which compensates for the shrinkage and reduced strength. Our product does that, virtually eliminating shrinkage even when using increased volumes of fines and substandard aggregates. Hardly any superplasticizer would have been required, much less cement required and no problem exceeding target strengths. And they would have saved significant dollars, not cents, on every yard.

It works because it utilizes all of the cement molecule and it provides a 3-Dimensional wrapping effect at the molecular level to achieve the higher strength along with better elastic and tensile performance. The Delft University, Witwaterrand University and Exterra BV studies and reports all confirm that this product does indeed create a stronger and more flexible concrete. All EU jurisdictions can now specify it's use, CSA and ASTM certification is next.
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George Clark
 
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