[peteeng]

Hi VNU - sorry modulus does not correlate well with compressive strength in high strength concretes. You do need to do a direct modulus test to figure this out. Engineering grouts are made by most concrete makers where are you? Thks for pointing out difference of SF vs FS. Learn something every day Peter

Hi Craig - steels at a macro level are like lego blocks. Each grain or block is held together by friction and in some cases intergranular mechanisms. The elasticity of the individual grains of metals are very similar, but the strength mechanics holding those grains together varies. So this is why "steels" and aluminums (metals) all have similar elastic properties yet different strength properties. The yeild strength of metals is when the grains start sliding over each other. They are held together by friction, their shape and other mechanics. These can be very strong like maraging steels or very weak like in irons.

So if you take some legos and glue them together with PVA glue and another block with super glue they will have the same elastic properties, but the super glued block will be stronger. Make sense?

In the case of concrete which is highly aggregate dependent compression tests are usually used and this biases the results. Compression strength is actually not a material property but closer to a geometric property. Gets complex, but if you have a relatively thin large round sample (like a pancake) you will get a totally different result to a tall thin cylinder... Peter

[vnuEndru]

Hi,
What sort of evidence do you have for that belief?

This is what academic papers say. It is true for concretes - concrete with higher compressive has higher young modulus than concrete with lower compressive strength. I think thats not true for other materials

Hi VNU - sorry modulus does not correlate well with compressive strength in high strength concretes.

As I said I saw proves to this in some papers, I'll try to find it. Maybe I'm wrong.

[peteeng]

Hi VNU - The concrete industry and some others have spent decades trying to find equations that make life a little easier for some of the engineers and the certifiers. I spent over 10 years doing the same in the advanced composites area. This is all a folly. There is no mechanical or physical relationship between compressive strength and the material modulus. This approach is called a calibration. We gather 1000's of bits of data and use some basic or complex polynomials to correlate the data the way we want. Not necessarily what is physically correct. So in the paper attached the author has spent a long time calibrating an equation to a data set and uses quite good statistics as well. Yet when I apply the equation to sika3350 it predicts the modulus based on 120MPa strength as 46GPa yet Sika publish the modulus as 56GPa. I could do the same by using the 5th planet of jupiters sunrise time to the moons rotation plus the USD value at noon every day and get the same sort of answer. Its a self fulfilling prophecy.

This sort of exercise suits academia. Not meant disrespectfully, but it fulfils the persons requirements to spend a couple of years doing something. The math's cannot be faulted and the industry meanders on with some more information or disinformation.

The correct approach is called "mechanistic" ie we determine the actual mechanism responsible for the phenomenon we want to predict and develop an equation that mimics the mechanism. This is not done by any of the academics in any of the papers that you are probably reading. The answer is quite simple test the product and measure its modulus. The Romans used an equation for designing stone bridges. It was based on some logic that seemed right at the time but was totally wrong. Some of those bridges are 2000 years old and still work fine, luckily. The timber and metal bridge builders for trains of the last century built 1000s of bridges using area methods that are totally wrong! and when a frenchman figured out how to use second moment of area methods for beams and proved the bridge eqn was wrong, the industry said the average engineer cannot figure out the second moment of inertia of a beam (only mathematicians can) so we will continue to use the old equation. Until some bridges fell down and that changed the blame game, So test your material for the property you need and consider some stuff carefully, it maybe wrong. Peter

[peteeng]

Hey Mike - How's the build going? Peter

[ozlemi]

Hello Peter,

As a chemist who develops materials for use in machine tools, the UHPC you developed caught my attention. I've also tried many mixtures for UHPC. I've failed in many of them, I'm just at the beginning of the road. I know it's pretty special, but would you please share your mixture recipe? In my experiments too much air left. (Even in nanodur ). Have you had such a problem? What are your test results? (Compressive and flexural strenght)

Ozlem

[peteeng]

Hi Ozlem - I suggest you use a commercial mix of engineering grout. They are self de-airing, self compacting. Sika and others have many varieties. I gave up trying to make my own when the concrete companies spend years developing mixtures and technologies. The UHPC/grout/CSA samples I have used are Bluey HE80 and HE80AG. Sika have a line of grouts that varies from country to country. I have some epoxy alox, epoxy steel and other stuff at a lab at present. Results due next month (june 2023) that will complete my materials investigation. The companies I have spoken to about their grouts have supplied compressive modulus & strength, tensile strength flexural strength. Rarely do they do tensile modulus as construction is not interested in this figure. The best one available to me local is Sika 3350 look it up in #63. Your a chemist?

For machine tool parts my current preference, disregarding cost is:
beryillium ( i found a source in the USA but had to sign too much paperwork to get it)
intermediate carbon fibre E=120GPa density=1500kg/m3. I suppose since cost is neglected I'd go high modulus (fibres are over 600GPa so laminate would be around 250GPa)
std modulus CF E=70GPa density = 1500kg/m3
sika 3350 E=55GPa density = 2300kg/m3
aluminum E=70 density - 2700
steel E=200 density = 7800

when the test results come in this may change. I also like titanium E=110 density = 4400 and beryllium E=287GPa and density = 1850. For reference cast iron is 100-120Gpa and density about 7500kg/m3 depends on its flavour.

Carbon Fiber and Prepreg Data Sheets | Toray Composite Materials America (toraycma.com)

Laminated metals are stiff and damp, so depending on what you want to do take your pick.... I pick cast stuff for production as casting in volume makes sense. For bespoke stuff laminated metal makes sense. About to make a router from laminated aluminium parts...Keep at it, it makes sense eventually. Peter

[ozlemi]

Sorry, I actually wanted to ask Mike. Thank you anyway. Sika was a brand I did not know, I will definitely try it.

[ozlemi]

Hello Mike ,

Could you please share your e-mail? How can i reach you?

- - - Updated - - -

Hello Mike ,

Could you please share your e-mail? How can i reach you?

my email : [email protected]

[Mr-MaW]

Hello Mike - The E80 UHPC material is very attractive but they could not tell me the tensile modulus. The E80 is the compressive modulus. The E80 they are reluctant to sell for machine use and they do not sell in small quantities and do not sell any product outside of the EU. E45 is relatively easy to achieve and my local concrete chemists can help with that. My other aim with developing a cold casting material was that it be machinable so surfaces can be finished accurately. Concrete can be machined with hard tooling and a wet machine. There is a local stonemason here with such a machine that expressed interest in machining my stuff but when it came to actually doing it he baulked due to the accuracy required. Headstones don't have to be very accurate.... Importing granite from china and having them machine it or locals machine it was an attractive route. But I decided against that method. Prefer to make my own moulds and use GF or CF to optimise shapes.

Carbon fibre ticks all the boxes and I use diamond tooling on my router for machining composites dry or wet. I don't think its expensive relative to the project. Make the parts with thick skins 10-15mm thick then back fill with CSA grout (or UHPC) I think is a cost effective approach. The CF I regularly make and test at E80 for yacht masts and industrial springs. So confident in that number (tension comp and flexure). Would make it at E70 to improve its shear stiffness and it would be a good all round material. You will need to get familiar with infusion to go down the CF path. Wet lay up and hand layup will not achieve the consolidation required to get to E50 or better. Peter

Hi,
I'm making small benchtop cnc mill and also decided to go with uhpc. This is first time I see someone making his own uhpc mix like me. I thought I'm the only one xD. I'm super interested in detail of your uhpc mix - proportions, what exact components did you use (especially silica fume and PCE), what your w/c ratio? Also as I can understand you didn't test your mix? I tested mine for compressive strength and it resulted in 110Mpa which is low, but its with high w/c. I succeeded in lowering w/c, samples are curing rn.

Hi VNU - Do not put much interest in compressive strength, but you need to test for its young's modulus. There are many commercial engineering grouts available and they are economical. If you only get 30GPa modulus you may as well use commercial mixes that get 40-50GPa modulus. I can buy non shrink grout with over 120MPa comp strength and 56GPa modulus at the local hardware in 25kg bags so why invent it yourself? Its water ratio by weight is 6-7%. Why are you using fumed silica in concrete? Hope your wearing a serious mask, silicosis is bad news.... Peter

Hello Mike ,

Could you please share your e-mail? How can i reach you?

- - - Updated - - -



my email : [email protected]

Nice to meet everyone.
If you need mineral castings.You can contact me, my email:[email protected]
I'm from China,My company has produced a lot of products, small can reach 100KG, large can do 46 tons.
My English is very average and I don't know how to upload photos. Very reason to share my product with you.

https://grabcad.com/library/cnc-lath...ral-castings-1

[suspension]

Hello Peter,

As a chemist who develops materials for use in machine tools, the UHPC you developed caught my attention. I've also tried many mixtures for UHPC. I've failed in many of them, I'm just at the beginning of the road. I know it's pretty special, but would you please share your mixture recipe? In my experiments too much air left. (Even in nanodur ). Have you had such a problem? What are your test results? (Compressive and flexural strenght)

Ozlem

I found this open UHPC mixture which may be of interest.
https://hiperfibersolutions.com/uhpc/

[peteeng]

Hi Sus - In the attached paper the best modulus was 56GPa. This was with 2% addition of steel fibers I think. No matter, E56 is not bad and they publish the recipe so go for it. Peter

[suspension]

Hi Sus - In the attached paper the best modulus was 56GPa. This was with 2% addition of steel fibers I think. No matter, E56 is not bad and they publish the recipe so go for it. Peter

I wont!
I feel there could be many things that can go wrong when trying to mix this. I am trying to find a construction grout that gives the strength I need. The highest strength grout I saw is the one you suggested Sika-3350. But still not sure how to handle its maximum thickness requirement and the fact that they don't give YM.

[peteeng]

Hi Sus - The sika 3350 quotes E56 and any grout is strong enough for machine parts. Its application thickness is 20-500mm how much do you want! Peter

[suspension]

Hi Sus - The sika 3350 quotes E56 and any grout is strong enough for machine parts. Its application thickness is 20-500mm how much do you want! Peter

hi Pete, what do you mean when you say any grout is strong enough? Wouldn't we need a minimum strength, like for example higher than 100 compressive strength in order to design a machine which is not too big.

[peteeng]

Hi Sus - Machines are designed for stiffness. This means that the stresses involved are tiny. You do not need a high strength material (what I would call high strength) for machine parts. 20MPa would do it. Peter

parts are designed for stiffness not strength, parts are huge so stresses are very low.

[suspension]

Hi Sus - Machines are designed for stiffness. This means that the stresses involved are tiny. You do not need a high strength material (what I would call high strength) for machine parts. 20MPa would do it. Peter

parts are designed for stiffness not strength, parts are huge so stresses are very low.

Basically what you are saying is the main parameter to look for is young's modulus (As this is what controls the stiffness mostly) and other parameters are usually more than enough to support the machine strength?

[peteeng]

Hi Sus - Yes - I have built a few machines from mdf and plywood and they have survived several large events. The mdf is less then 20MPa strength and the plywood is usually F17 which means its bending strength is 45MPa. F17 ply has a modulus of 14GPa so you can do better than that. Solid timber parts with metal laminates can do amazing things. Damp and very stiff... Structural Plywood is a highly specified and engineered material. Many people build out their machine from plywood then once built use it to make the metal parts as replacements for the ply. Some just stay with the ply... Peter

https://www.bing.com/ck/a?!&&p=f251a...QUwucGRm&ntb=1

[ardenum2]

the point to cold casting for machining is not to optimize the shape, just to cast a monolithic object. Cold castings get optimized when its usually for something other than machining like semiconductors. even then shape optimizations is rudimentary. If you want to cast in grout don't optimize just make it a block and stick a cooling pipe in the middle. If you're optimizing than it only makes sense for iron casting.

if sika 3350 is 500mm max. pour thickness that's enough for anything you'll ever need. I don't know if you can add fibers to grouts but if you could I'd avoid steel and consider non metallic fibers that ideally would also bond with the grout instead of just mechanically interlocking inside it.

[suspension]

The only reason to do shape optimization is to reduce required material in my case.
Sika 3350 seem to be the way to go, but I think I will have to import it from UK or USA.

I also found this one which is locally available. It specifies YM also:
https://www.chryso.lk/p/8921/3/5636/en

YM = 47
Compressive strength = 85

I am waiting for the pricing from the local agent. If its reasonable, I can use a thick blocks for base and column. But this has a maximum thickness of 100mm. According to datasheet, higher thickness requires addition of aggregates. How does addition of aggregates affect YM and strength? I believe I will have to do some tests and see?

[peteeng]

Hi - Its good to optimise the shape but in reality the options to do this is limited. The shape of the part is not material or material strength dependent. It will look the same whether concrete, chewing gum or metal. The optimal part is the biggest object you can get into the space allowed. Then make it hollow until its rigidity is affected. This is a simple but effective approach. In the case of timber and low modulus materials like normal concrete just make them solid.... there's no point in trying to carve off weight. Steel and cast iron at 7800kg/m3 yes there is a point in loosing weight. But aluminium and concrete at <2700kg/m3 means solids are not very heavy. Plywood at 700kg/m3 means its really light... just add some metal at critical places and you have a light stiff damp structure... Peter