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Name:   
Heading: 1.1.4.3.2.1.1.1.1.1.1.2.2.1.1.1Aggregate 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


To Grant Gardner

When we use the HP cone to make sand the closed side setting is 5/8 to 3/4. The feed with recirculating load is about 75 % passing 1/2". This forces the case of autogenous (rock on rock crushing).

It would be far better if the ASTM would recognize that the minus 200 mesh x 325 mesh material in manufactured sand is not detremental but ICAR has been trying to get that done for over 10 years. Maybe once it gets to be common place in Europe it will be adopted in the USA.

I spent 25 years as a plant manager of both concrete and aggregate production. Working on Highway construction projects, commercial concrete production, Dams Power Plants and Tunnels. However I am not a Cement chemist so I can see you have some valid points.

John Googins
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John Googins


John, it is good to hear that you have the same problems in the U.S. with ASTM as we do in Europe with the EN. So dont count on the Europeans to lead the way.
The EN 206 for concrete in Europe has been a step back. Each country is having a different WCR/WBR for the same mix, as long as we do not agree on what "cement" and what a "binder" is! And aggregate is even more a local issue.

Prescription based standards have to be banned in order to progress towards Performance based concrete or asphalt.
We should liberate ourselves from standards that are concensus based and directed by conservative and dominant market forces such as the cement industry.

The industry has to grow up and look at WHAT we can produce and not HOW. If we believe that adding micronized dogshit is good it is nobodies business, it is the final performance that counts.
The only standards we should have should be for testing methods so we can compare the final results of our products we are responsible for.
Please get the P2P initiative on track again in name of progress and the environment.
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Boudewijn Piscaer


I strongly support Boudewijn's viewpoint. For more than 20 years concrete producers in Australia have had their own excellent laboratories and technical staff and have been free to use them to develop, use, and continuously adjust concrete mixes to give greater economy and closer quality control, initially using my Conad system. Producers in many other countries have subsequently adopted the system, including its use on Petronas Towers in Malaysia to produce high strength concrete at a variability so low that ACI refuses to believe it (preferring to believe that coefficient of variation is the relevant criterion, rather than admitting poor control of high strength concrete).
Many producers in USA are using the system to some extent but are prevented from using it properly by inept specifications.The practice of specifying proportions increases cost and keeps in business producers deficient in knowledge, skill and facilities. Naturally people who earn their income by writing such specifications, or are defended from more competent competitors by them, are going to continue to vote for the status quo, so how is the USA to progress?
Incidentally it would help if George Clark presented some of the factual information from university tests to which he refers (or refers us to a website)rather than making a blanket claim which must have limitations.
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Ken Day


Hi - in the uk a lot of the RMX suppliers are now using limestone dust from the hard rock quarries in the process as a % of fines - typically circa 30% of fines. This has in some places found a reduction in cement content but generally netted of the effects. it creats a good creamy mix and increases the pumping ability for the high rise work. sometimes this is washed but we try to keep it all in to save costs. this is mainly done to rid the quarries of there excess product and improve return rates. biggest problem is getting the material to flow in the bins due to the humidity in the UK. can often worm hole which has obvious problems.
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stewart cameron


Are those that produce mfg. sand producing it wet or dry? What equipment is being used?
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Travis Hibshman


Travis,
This is a big question - I can give you a run down on the range of options, wet or dry, if you contact me at hugo_pettingell@hotmail.com.
Hugo
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Hugo Pettingell


Hi Ken, Jay, David and others

Concrete is made when particles in 3D space bond together through chemical reactions and physical inter growth in varying proportion depending on the type of concrete. In hydraulic cements these chemical reactions conveniently involve hydration so sufficient water can be added to plasticise the particles for placement. Of all the above commentators my money is on Grant Gardner as all the points he made are most relevant, especially those concerning mineralogy and particle packing. Strength may be more or less when crusher dust is added depending on the mineralogy, reactivity, packing and resulting water demand etc. and also whether there is competition with cement particles (the most reactive) for 3D space. This is the science behind the recent shift in standards to allow limestone fines to be included in cements.

The devil is in the detail however so in relation to the original posting it is not possible to easily generalise by prescription as standards and green rating systems attempt to do. Given the right grading and mineralogy crusher dusts can be added and improve properties. Because so many factors are relevant and the results of doing so can vary prescription can lead to problematic results. The addition of crusher or any other mineral dust is an example where permissions and rewards systems like green points fail and I have argued extensively for performance based criteria in relation to same ( See http://www.tececo.com/sustainability.permissions_rewards.php). In the case of crusher dust a simple measure of embodied energy and emissions for given properties of the resulting concrete would be much more suitable for green rating.

John Harrison
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John Harrison


Boudewijn Piscaer I would love to chat to you re the CCF use in concrete. could you email me if you get a chance. Trevor@mortimerquarries.ie

Thanks in advance
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trevor mortimer
 
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