[suspension]

Yes and no:-) I didn't get the institute to do the testing. Mostly because the ones i talked to usually "just" test concrete and their main focus is compressive testing, which isn't very usefull for my/our purpose. I ended up being assured by the videos of Stefs machine performing very well, so i ditched the "official testing" and went on with my casting...

However, i'm not done using EG and i have other projects in mind. But the next time around, i'm going to try to solve some of the issues i have had in my project: Mainly proper simulation models and proper degassing during casting. I've been thinking about doing the flex-testing(just as you) for quite some time, but haven gotten around to do it yet. But this is defently something i'll need to do before any new projects with it. I no longer think i need "official help" from a 3rd party to validate the stiffness of the EG, so i'll just to the testing myself. Peter(and you now :-) ) has posted quite a lot on this forum about this, and i like the idea of testing a known material first, like aluminium, to validate the process before testing own samples.

I've also been thinking about solving the degassing part by curing the casting under pressure. This is a whole other beast to tackle, but nonetheless something that defently will affect the stiffness and strength of the final casting. From my casting this is how a "cross-section" looks like:

I've tried degassing the mix, but it was not possible with my mix, the gas simply could not get out, even under "full" vacuum. The next step would be to try to add an additive to the mix that allows better degassing, but this might also affect the shrinkage of the casting and might not be desireable. So to minimize the airpockets i would like to try to cure it under e.g. 10bar of pressure to effectively shrink the "bubbles" to 1/10 of their normal size. This doesn't remove the air, but my hope was that it would minimize the effect of the trapped air. However, this does come with its own set of problems(and dangers!) but it might be a way...

/Thomas

Hi Thomas

I also ditched the 3rd party testing due to exact same reason - All of the institutions I talked to were mainly focused on civil engineering and not in this sort of application. I re-did the flexural modulus testing with the sample and got very similar results (30) for my grout.

These days I am doing the shrinkage tests for the grout - which seem to be more challenging though. But based on the tests so far, the grout mixture seem to shrink even through its been more than 30 days old now. This made me look in to materials again. Each option seem to have its own problems and uncertainties. With EG, the biggest issue seem to be low flexural modulus - I have seen a thread in this forum where a professionally created EG mix only gave 12! However I doubt there are other issues with EG such as cracking/shrinking and inability to handle dynamic/impact loads? Did you do any research in this area?

There seem to be even less information about UHPC/Grout case. Alex who built a CNC with durcrete mentions that there was considerable shrinkage. Not sure if this shrinkage is limited to fist days only. Also, there seem to be only two companies operating in this area, durcrete and rampf group. Rampf's epuself is super expensive. They dont seem to sell the other material they produce. I wish if Alex can give us some info on the shrinkage/accuracy of his CNC which I think is few years old now. Also do you know if Sef's machine give consistent accuracy with in say 10um tolerance?



Thanks
Sus

[badhabit]

[...] I re-did the flexural modulus testing with the sample and got very similar results (30) for my grout.

These days I am doing the shrinkage tests for the grout - which seem to be more challenging though. But based on the tests so far, the grout mixture seem to shrink even through its been more than 30 days old now. This made me look in to materials again. Each option seem to have its own problems and uncertainties. With EG, the biggest issue seem to be low flexural modulus - I have seen a thread in this forum where a professionally created EG mix only gave 12! However I doubt there are other issues with EG such as cracking/shrinking and inability to handle dynamic/impact loads? Did you do any research in this area?

There seem to be even less information about UHPC/Grout case. Alex who built a CNC with durcrete mentions that there was considerable shrinkage. Not sure if this shrinkage is limited to fist days only. Also, there seem to be only two companies operating in this area, durcrete and rampf group. Rampf's epuself is super expensive. They dont seem to sell the other material they produce. I wish if Alex can give us some info on the shrinkage/accuracy of his CNC which I think is few years old now. Also do you know if Sef's machine give consistent accuracy with in say 10um tolerance?

I haven't done much research into EG vs. UHPC, it mostly seems like a "religious war" and in my opinion there is not a clear "winner". The biggest downside to UHPC (as far as i've research!) is that it behaves like a concrete(duh!) so it keeps "moving" for a very long time. EG does not, but it then have other properties that are undesireable(toxic before hardening, non-newtonic makes degassing problematic, it is a plastic makes process "dirty" and recycling hard etc) and EG is very(purely) dependent on the aggregate to get a good result(=high modulus)..

A modulus of 12 seems wrong, epoxy in itself is something like 3-4ish. So 12 seems low...i would expect at least double for a "professional solution".... i really need to do the test on my(and Stefs) mix using Silimix282... What was the coupon-size you cast for the test you made? Were your samples "perfect smooth square" or did you have an "open side" on your mold giving an rough side? I was thinking about casting a 800x20x20 coupon and stuffing it from the end making all sides smooth, but i'm worried about the air affecting the result "unfair" due to the narrow cross-section...and making the crosssection bigger increases the forces required to make deflection very quickly....

I haven't seen any information from Stef regarding accuracy tests for his machine, but his surfacefinish looks spot on(in aluminium though)....so that is mainly what i based my comment about Stefs machines performance on....

/Thomas

[suspension]

I haven't done much research into EG vs. UHPC, it mostly seems like a "religious war" and in my opinion there is not a clear "winner". The biggest downside to UHPC (as far as i've research!) is that it behaves like a concrete(duh!) so it keeps "moving" for a very long time. EG does not, but it then have other properties that are undesireable(toxic before hardening, non-newtonic makes degassing problematic, it is a plastic makes process "dirty" and recycling hard etc) and EG is very(purely) dependent on the aggregate to get a good result(=high modulus)..

A modulus of 12 seems wrong, epoxy in itself is something like 3-4ish. So 12 seems low...i would expect at least double for a "professional solution".... i really need to do the test on my(and Stefs) mix using Silimix282... What was the coupon-size you cast for the test you made? Were your samples "perfect smooth square" or did you have an "open side" on your mold giving an rough side? I was thinking about casting a 800x20x20 coupon and stuffing it from the end making all sides smooth, but i'm worried about the air affecting the result "unfair" due to the narrow cross-section...and making the crosssection bigger increases the forces required to make deflection very quickly....

I haven't seen any information from Stef regarding accuracy tests for his machine, but his surfacefinish looks spot on(in aluminium though)....so that is mainly what i based my comment about Stefs machines performance on....

/Thomas

I just glanced through this paper - which surveys many previous research on this subject (Only epoxy based I think). And it shows a table of various previous researches. For me it looks like many of the researches report EM below 20 for EG. This seem to be agree with Pete's observation of 17 GPA.
Since the aggregates I used had max size of around 15mm, Pete suggested I have a minimum cross section of at least 40mm and length of 800. So my specimen was 50x50x1000mm. Its was a full solid block/beam. It was not that difficult to deflect. I applied forces starting from 4Kg up to 17Kg and measured the deflections which ranged from 3um to 16um.