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Heading: 1.1.4.3.1.1.2.1.1Aggregate Fines
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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


"Aggregate Fines" covers a multitude of sins - from downright rubbish to properly shaped and graded material that is comparable in performance with natural sand. It all depends on production technique...
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Hugo Pettingell


I currently run Quarries in South East Queensland, Australia producing around 6 million tonne per annum supplying an internal concrete business. Around 15 years ago we began introducing crusher fines (Manufactured Sand we call it) into the concrete mix.
For the last eight years or so the volume of Manufactured Sand in the concrete mix has been at around 60% of the total minus 5mm in the mix. This volume of Man Sand in the mix remains unchanged in mixes requiring strenths of up to 80mpa at 28days without the use of large quantities of superplacticisers nor have we suffered from negative impacts from water demand, shrinkage etc. Cement contents are way down on what they were 15 yrs ago.
I do not suggest that these results would be obtained everywhere as the quality of the fines and the production process plays a pivitol role in the successful use of the product.
Today I have to build crushing plants that can produce Man Sand at up to 40% of total production capacity or modify existing plants to produce more minus 5mm to keep up with demand.
Happy to provide info to anyone interested or answer some questions.

Dave Parker
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Dave Parker


Dave, thanks for confirming my findings that more fines does not mean more (portland) cement.
I am curious to know if you were just lucky with the type of manufactured sand and compatibility with the cement or if you investigated particle size distribution of the fines. With other words, was it trial and error as still very common in our industry or if you did "particle size engineering" investigating the PSD under 90 microns.
I also would like to know if the type of particles and surface tension plays a role? A study on 12 calcium carbonate fines (CCF) at the University of Leuven on the particle shape were not conclusive.
Maintaining the same PSD we did use different grinding techniques for CCF resulting in different shapes but we obtained the same performance.
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Boudewijn Piscaer


I'm sorry to say that I get lost in the detailed science that some contributors find familiar, particularly the effects of magic admixtures, but it seems to me that we who have to do the rock-breaking are constrained by what our machines are capable of doing. Broadly that means we need to produce the best particle shape we can, fit a particle size distribution that avoids the tendency for bleeding, and control the level and, as far as possible, the gradation of microfines, and above all, do it consistently. In Japan, the loss of natural resources over many years has led to the development of an integrated system of crushing, psd adjustment, and fines control that seems to tick the boxes in a practical sense, and good resuls are obtained using the product as 100% replacement for natural sand.

hugo_pettingell@hotmail.com
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Hugo Pettingell


Boudewijn, the Cement Concrete and Aggregates Association in Australia has recently release several good papers on the subject on their wesite www.ccaa.com.au can I suggest that you take a look. Hope this helps.


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Dave Parker
 
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