Large Epoxy Granite Vmc Project

[dracozny]

that is some thick stuff. tempted to experiment myself on the matter. too many projects as is though.

 

[H8deadW8]

I like the idea of adding gallon batches of resin to the aggregate. The aggregate acts as a thermal sink to reduce exotherm, which is limited by the specific heat capacity of the filler. If I was going to try this and had to use commercially available resins, I would look at RTM (resin transfer molding) resins-- these also go by names like VARTM and vacuum infusion resin, but the resin is essentially the same. RTM resins have low viscosity like the US Composites material (600cps = 0.6Pa.s), but often have very long gel times. Adtech, PTM&W, and Resin Services would be the first places I looked. It would be really fun to formulate a resin for this application-- we could get pretty tricky and increase the working life to 12 hours, add air release agents to help it degas on its own, and pigment it for aesthetics. If anyone has a commercial interest in this, let me know-- I work for an emerging technologies group that can do contract research.

Development of a filler system to achieve maximum filler loading is nontrivial. You can get nerdy and try to calculate it, but you generally have to make the assumption that all of the filler consists of spheres that are consistent in size. A direct approach would be to fill a container of known volume with your largest size filler. Then you add water to fill the void spaces. So you might take a 1 liter container and find that the water required to fill the void spaces is 400mL, hence your system is 60 volume% filled. Next, assume your second largest filler could take up a maximum of 400mL, but if packing efficiency is 60vol% again, then you would end up placing 240mL of small filler in the voids left by the large filler. The problem is that the second filler will likely have a different packing efficiency than the first-- so perhaps you perform 3 experiments at different ratios, maybe 65,60, and 55vol%. Do the water displacement on these to determine the best amount of the second filler to use. Assuming 60vol% turns out to be the ideal ratio again, the void space you would measure would be 160mL, so your system is 84 volume% filled. Note that if the small filler is only 1/2 the size of the big filler, it will not fit into the voids between the big filler, and the packing efficiency will be poor. Ideally, the second filler should be 1/10 to 1/20 the size of the first. You could repeat the testing procedure to add a third filler, though at some point I am sure you would have trouble getting air bubbles out of the filler/water test container. A little soap might help with that. Anyway, moving down to smaller and smaller fillers is a game of diminishing marginal returns, and smaller fillers have a larger effect on the viscosity of the final system due to their high surface area. If anyone decides to go down this rabbit hole, remember that to get from the weight of the filler to its volume, you need to divide by the filler's density. So 84vol% filled will not be 84 weight% filled, unless your filler has the same density as the water (or resin). Sorry about the nerd out!

Best of luck with this project, and please keep us updated.

Nic

 

[gt40]

I like the idea of adding gallon batches of resin to the aggregate. The aggregate acts as a thermal sink to reduce exotherm, which is limited by the specific heat capacity of the filler. If I was going to try this and had to use commercially available resins, I would look at RTM (resin transfer molding) resins-- these also go by names like VARTM and vacuum infusion resin, but the resin is essentially the same. RTM resins have low viscosity like the US Composites material (600cps = 0.6Pa.s), but often have very long gel times. Adtech, PTM&W, and Resin Services would be the first places I looked. It would be really fun to formulate a resin for this application-- we could get pretty tricky and increase the working life to 12 hours, add air release agents to help it degas on its own, and pigment it for aesthetics. If anyone has a commercial interest in this, let me know-- I work for an emerging technologies group that can do contract research.

Development of a filler system to achieve maximum filler loading is nontrivial. You can get nerdy and try to calculate it, but you generally have to make the assumption that all of the filler consists of spheres that are consistent in size. A direct approach would be to fill a container of known volume with your largest size filler. Then you add water to fill the void spaces. So you might take a 1 liter container and find that the water required to fill the void spaces is 400mL, hence your system is 60 volume% filled. Next, assume your second largest filler could take up a maximum of 400mL, but if packing efficiency is 60vol% again, then you would end up placing 240mL of small filler in the voids left by the large filler. The problem is that the second filler will likely have a different packing efficiency than the first-- so perhaps you perform 3 experiments at different ratios, maybe 65,60, and 55vol%. Do the water displacement on these to determine the best amount of the second filler to use. Assuming 60vol% turns out to be the ideal ratio again, the void space you would measure would be 160mL, so your system is 84 volume% filled. Note that if the small filler is only 1/2 the size of the big filler, it will not fit into the voids between the big filler, and the packing efficiency will be poor. Ideally, the second filler should be 1/10 to 1/20 the size of the first. You could repeat the testing procedure to add a third filler, though at some point I am sure you would have trouble getting air bubbles out of the filler/water test container. A little soap might help with that. Anyway, moving down to smaller and smaller fillers is a game of diminishing marginal returns, and smaller fillers have a larger effect on the viscosity of the final system due to their high surface area. If anyone decides to go down this rabbit hole, remember that to get from the weight of the filler to its volume, you need to divide by the filler's density. So 84vol% filled will not be 84 weight% filled, unless your filler has the same density as the water (or resin). Sorry about the nerd out!

Best of luck with this project, and please keep us updated.

Nic

Thanks for all the info. I am nearly done with the mold and have been busy radiusing all the inside corners and completed alignment and test fit of the rails - better to do this before you pour epoxy.

I have a couple of questions:

1. What would you suggest for air release agents for the US composites epoxy I already have?

2. What would you suggest as a cost effective means of mixing all of this? I leaning towards the polymer tub gas powered cement mixer from home depot- It is a fall type basically a big plastic barrel with fins inside.

3. If I went the cement mixer route, how do you clean it?

Thanks, in advance for any ideas

 

[Eddyde]

As far as cleaning a mixer, Xylene is usually a good solvent for epoxy but it would still be a real mess to deal with and you would have the issue of sludge disposal. Are you planning to rent a mixer of buy one? If you buy you only need to scrape off the bulk of the residue, subsequent mixes will slowly build till the drum is useless, but I suppose you would get quite a few batches before that happens. Also why a gas mixer? an electric will do the job albeit in smaller batches, they are way cheaper too. I have an electric that will easily mix about 250lb batches of regular concrete.

 

[gt40]

Thanks for the suggestion on Xylene- it is banned here in the peoples republic of ca. I ended up finding a 90 gallon giagantic 90 gallon mixing tub.
I also picked up a 1000 lbs of aggregates and sand and rinsed about 300lbs of the larger size.

I was able source everything local to avoid shipping costs but the "flour" portion made up of powdered quartz and alumina- I got that online from the big ceramic store 50lbs for 50 bucks including shipping. FYI, it really does feel and look like fine flour. Everything else came from Home Depot and the local West LA Building Supply store.

On top of that, the epoxy came:




Supplies:

Decomposed granite, 60 grit sand, small pebbles and a giant 90 gallon mixing tray:




Unloaded:

Each sand bag is 100 lbs and the rest are 50 or 75lbs + more in the garage



I am easily amused but the mixing tub really is awesome- you can mix the whole batch in one shot.



Here are the different aggregates:





To promote adhesion, you need to wash them and let them dry properly. The decomposed granite was really dirty:





Here is a close up of the 2 types of large stones from Home Depot:




smaller grades:



30 and 60 grit sand also- I didn't have to wash that because you can buy graded washed and kiln dried fairly cheap in 100 lb bags.


Here is a close of the mineral "flour"



I used epoxy tile grout with a large radius form to creat a 3/4" radius on all inside corners of the mold:



Radiusing the corners makes it easier for the mold to release and the final base won't have sharp edges...




Well, my arms are sore but I hope to be able to pour the mold this Saturday- forecast is 59/74. FYI, anyone local to Santa Monica who wants to hang out and see me make a mess, I could sure use the help! Pm if you can make it

Thanks,

 

[sgisler]

Wish I were closer, would be interesting to see it come together and would be glad to pitch in (quite a drive from Dallas though).


Sent from my iPhone using Tapatalk

 

[Boswell]

Looking forward to seeing your progress each day. Thanks for sharing. Good luck this weekend.

 

[gt40]

FYI, here is the mix I have come up with. I really wanted to use local aggregates wherever possible to save shipping and reduce overall cost. Empirical observation and practical considerations are the basis for the mix:

 

[gt40]

Update:

I have washed all of the aggregate and have it drying spread out on tarps. For anyone wanting to work with epoxy granite, it is important to wash, clean and dry the aggregate. I washed it by filling 5 gallon buckets with material and then stuck a hose into it and washed it until the water cleared. The larger stones weren't bad but the decomposed granite is really dirty. Afterwards, you spread it out on something to dry. Tarps make it easy. This step is important for proper bonding with the epoxy as the fine dirt and any moisture will mess things up when you go to mix. It is taking about 3 days for things to dry - I have raked it out to rotate stuff each day when I come home from work. Looking forward to casting the base this Sunday...

 

[chrisf]

Awesome build so far!! Where did you get your flat stock? Msc had it for 202.00 each.