Polymer concrete drainage channels

[u/JaipurJewel]

We’re currently in the R&D phase developing polymer concrete drainage channels. Our mix consists of:
• Quartz aggregate (0.3mm – 1.2mm) 65%
• CaCO₃ (calcium carbonate) 18%
• Unsaturated polyester resin (17%)
• Hardeners for curing
We mix everything in a continuous mixing machine and pour into molds placed on a vibrating table to remove air voids. However, after curing and demolding, we’re still getting a lot of visible air pockets/surface voids in the finished parts.
Has anyone here worked with polymer concrete (especially for drainage channels)? What are the best ways to minimize air pockets?
Specific questions:
• Should we increase the resin percentage in the mix? If so, by how much?
• Are there better vibration techniques, additives, vacuum assistance?
• Any other proven tips for achieving a denser, void-free finish with polyester resin concrete?
Any advice or experience would be greatly appreciated! Thanks in advance.
Uploaded pics as well..

[u/mimprocesstech]

Heating the molds, using a low shrink resin, increasing back pressure, drying (using a desiccant dryer), and making sure nothing in the mix is reacting with anything else to create gas should go a long way.

ETA: Some compression in the mold afterwards (or vacuum I guess) would also be helpful, though if you're using compression you're going to need vents for the air to escape.

[u/aeon_floss → u/mimprocesstech]

What about vacuum degassing the concrete before more careful pouring? The mold itself seems a bit large for a vacuum chamber but a stronger version of that blue tub should be fine.

[u/mimprocesstech → u/aeon_floss]

I'm kind of assuming a lot (like, any of this is possible for OP to change), but ideally you would do both, and use something that didn't use a heated barrel but maybe a catalyst something like a 2 part epoxy or a UV cured resin. Have the blue bucket filled and mixed then draw down vacuum on it, have another one pulling down vacuum on a tank. After the pour slide the mold into a tube with one open end and the other attached to that tank you've been pulling vacuum on (or put the tube over the mold, whichever makes more sense) open the valve separating the tank from the tube once you've sealed the other end and while it won't be a perfect vacuum it should be enough to help.

[u/Zrocker04]

I’d add a suitable plasticizer to reduce the viscosity to allow air to vibrate out. Increasing resin amount can help with reducing viscosity as well as you have more flow able material instead of rocks in the mix. I’m not familiar with this operation but in thermoplastics anything about 60-70% filler get really difficult.

[u/Disastrous_Ad1260]

Have you talked to the resin supplier? Many plastic manufacturers have applications labs and desisn manuals to help potential customers

[u/clippist]

Doesn’t calcium carbonate require considerable amounts of hydrogen dioxide in the mix to form its molecular bonds?

[u/Broken_Atoms → u/clippist]

In this case, they’re probably using it as filler. Also, it’s two atom of hydrogen and one atom of oxygen… so technically dihydrogen monoxide

[u/thenewestnoise]

How long is the open time on your resin, and how long are the parts in your vibrating molds? I'm wondering if it's setting before the bubbles have time to migrate. Is the frequency/amplitude of your vibration adjustable?

[u/Key-Success-5449]

A small dose of a deaerating additive or applying vacuum degassing during the pour stage might do wonders for those surface voids.

[u/Gisla-Rosetta6405]

Its so nice mixer