Torsional Beam Fill: EG vs Concrete

[StudioMachinist]

I have to ask, is this for strength or dampening?

If dampening the dry sand is way better than grout or cement. The sand does a great job of adding heft, and reducing vibration.
If looking for more strength, both grout and concrete offer that. I would think concrete might be better by a small margin, but both are difficult to get fully loaded without a rod to compress and knock out the voids. You can probably fill them after cutting and before welding. That way you get are assured a good packing.

Strength. I didn't think it would be necessary but it wouldn't be hard to pre-stress it.

 

[jwmelvin]

I have to ask, is this for strength or dampening?

For dampening, just throw it in a lake. Sand may help with damping.

Don’t think strength is at issue, but stiffness will be important.

Hydraulic cement would be the thing for a cementitious product, as it is designed not to shrink. And I don’t think you’d want polymer-modified cement, as you won’t get the appropriate drying.

 

[StudioMachinist]

For dampening, just throw it in a lake. Sand may help with damping.

Don’t think strength is at issue, but stiffness will be important.

Hydraulic cement would be the thing for a cementitious product, as it is designed not to shrink. And I don’t think you’d want polymer-modified cement, as you won’t get the appropriate drying.

Another option is anchoring cement (that's what quikrete calls) that actually expands as it cures. I don't think it expands enough that it would deform the beam but that is something to figure out.

 

[RJSakowski]

Portland cement doesn't dry by exclusion of water. The water combines with the cement to for a hydrated compound. Pouring within a closed space should be fine. Portland cement also doesn't fully cure for a considerable time after mixing. Studies at UW Madison involved strength vs. time for a fifty year period. They found that after fifty years, the concrete was still increasing in strength. They had enough samples to continue the study and extended the study to another fifty years. For a closed beam, the rigidity is determined by the tensile strength of the shell and the incompressibility of the filler. I would expect that either the EG or cementitious filler would be similar.

If using EG, having a closed form and the ability to pull a vacuum on it would be an effective way to reduce voids. For 6 years, I worked for a medical device company and we had a series of epoxy composite products. We mixed the epoxy and poured into molds in a vacuum chamber. The molds were then pulled from the chamber to cure. Our products were CT scanned for uniformity and this method was effective at preventing voids.Going the other way, pressurizing the mold while curing after a pour will also compress the voids. The best approach would be a combination of the vacuum followed by pressurization.

 

[pontiac428]

For dampening, just throw it in a lake. Sand may help with damping.

Thanks for that. I have been fighting to resist the jerks and eye twitches caused by my internalized ire for abuse of the language.