Benefits of an Epoxy Portland Mix for repair

[darr]

Hello,

I am hoping there is a materials engineer that can answer this question for me.

We manufacture a material for the construction and repair of Ferro based boats, a synthetic mortar mix that is currently designed to work with Polyester resin.

I understand the chemical composition of our material pretty well for a non materials engineer.

What I cannot understand and would like explained to me is the benefits of using a 2 part Epoxy resin with Portland cement to create a patching material.

What chemical reactions if any occur?

How does the addition of the portland affect the creation of the linked chains in the epoxy structure?

Isn't it basically the same as thickening epoxy with talc?

[Herman]

For as far as I know, the epoxy will not interlink with the cement, so it will just be a filler.

I guess you are better off using chalk, last time I got it offered it costed 5 euros per ton, but I had to pick it up in a dump truck.

Talc (Microdol for instance) is also a valid option, and cheap. Even fine sand or quartz can be used. (search for a sand supplier which supplies filter companies.)

The advantage I see with epoxy is the better adhesion.

[mcollins07]

I have some interest in the interaction of the Portland cement and polymers also. I have not looked into this very much and would be very interested in what others might have to say about these mixtures. From what I’ve been reading on the net, the Portland cement system and the organic polymer systems (either polyester or epoxy) don’t seem to mix very well.

The Portland cement is a mixture of Ca0, Al2O3, SiO2 and perhaps a few other minerals. The proper mixture of these will react with water to create the cement. A small amount of water is consumed by the reaction. And the CaO makes the system alkaline.

The polyester is hydrophobic, it does not mix well with water. Although the ester monomer is typically catalyzed with a peroxide, I think the CaO (strong alkaline) can also contribute initiating polymerization of this monomer. The amount of water present during polymerization also affects the rate and extent of this reaction. I think mixing these chemical systems complicates the system and make predicting the rate and extent of polymerization extremely difficult. The material properties of the mixed polyester is not likely to have properties as desirable as a simple polyester from a more predictable (simpler) system.

The epoxy is a hydrocarbon monomer with polymerization initiated by some type of peroxide also. Again the polymer is still hydrophobic, but the reaction is not significantly effected by the presence of water. People talk about an amine blush regarding epoxy, an amine by product coming to the surface. An amine is alkaline, so a naive chemical view is that an alkaline by product suggests that an alkaline environment will not promote the reaction. Also, epoxy is generally a better glue and stronger polymer than polyester.

If you take the view that the inorganic cement plays a role as filler, then the epoxy should make a better glue to glue all the components together. The epoxy’s polymerization reaction is probably less effected by the presence of the alkali and water. The results are probably easier to reproducible with the epoxy system and don’t age as significantly. By aging I’m referring to the chemical reactions that occur after the material in initially made. So, epoxy is probably a better choice to attempt a complex organic/inorganic polymerization system. Epoxy is a better choice because it is less affected by the presence of the cement, and has better bonding properties.

I question can you really get any better material by carrying out the organic polymerization and the inorganic polymerization (cement) simultaneously, and together, than by simply adding concrete particles as a filler. Or in the case where desiring the bonding properties of the cement, to first apply the cement and then encapsulate the cement in epoxy after the cement is well cured.

[mcollins07]

A third option occurred to me, which I think might be most desirable in repairing ferro-cement boats. I’ve heard that the old concrete and new concrete don’t bond well. Reports on how to build ferro-cement boats say it is important to build the entire hull in one lay-up.

So, in order to gain the bonding properties of the epoxy and still maintain the economy of the cement, put a layer of epoxy in the repair site and while the epoxy is still wet, apply the cement for the bulk of he repair volume.

Anyone tried this? What problems do you see?

[darr]

Hello Mcollins07,

To my knowledge they are not using water in the mix, which I think would be a disaster to start with.

Would the use of Portland as a thickener not make the epoxy more brittle?

I would prefer to see a flexible material to be used as a patch to minimize the possibilty of a break in the bond between the concrete and the patch when the hull flexes.

I know that basic epoxy is supposed to be more flexible than basic polyester resin.

However in tests that we are running, we are finding the portland epoxy mix to be very brittle, and prone to breaking with repeated impacts.

We also find that it does not deform very well, and always results in a catastrophic break when we put it in the flex test.

I would be interested in exploring the modification or redesign of our base product for use with epoxy, if I can understand then find what I need to modify it with to have the same toughness, flexibility and ease of use of our current proven polyester based product.

[Herman]

You could also investigate the possibilities of waterbased epoxy systems, or waterbased polyester systems. These are readily available in Europe, do not know the situation in USA.

[mcollins07]

Darr,
Viewing it as a simple binary system of filler and epoxy, if you increase the ratio of epoxy you should get properties more similar to the epoxy polymer. So using a greater amount of epoxy relative to the amount cement, one would be expected to get better results. And although varying the ratio should be done, in order to characterize the system, this might be only very slightly better results.

I suspect a more productive route is changing the properties of the filler. One can significantly change the properties of a cement/aggregate particles. The amount of cement relative to the aggregate (sand), the size of the sand particles, and the size of the resulting filler particle will all have an influence on the resulting material.

Are you currently mixing cement from the bag into the mixture, or do you make a cement/sand mixture and then crush it up? What is the ratio of the cement to sand? What is the starting size or mesh of the sand? The size of the particles after crushing and sifting ?

You probably want to go for a higher aggregate to cement ratio, and larger aggregates, and larger resulting particles size of filler in order to get more flexibility, but you would have to try it to be sure. The results that your epoxy system is weaker than the polyester system surprises me. Which reminds me that the details of the particular system are very important and the test are always more authoritative than simple theory.

If the epoxy is reacting with the cement to become more brittle, most likely it is because of the CaO in the cement. If you measure the alkalinity of the cement prior to mixing with epoxy, you should find a correlation between alkalinity and brittleness.

Also, by casting the cement/sand letting it cure and then breaking it up to an appropriate particle size, you would reduce the alkalinity. Because the CaO is reacting with the Al2O3and SiO2 and is not available to react with the epoxy in a subsequent step.

[Herman]

Very basic question:

What is the advantage of cement in epoxy? Bonding to old cement?

[goodwilltoall]

Dave Carnell has had experience using lime and portland cement. It probably is just a filler and does not bind moleculry, but did seem to make it stronger in abrasion. Do a search for Dave Carnell + epoxy.

[darr]

No, we do not use the mixture, I have had a couple of clients suggest it.

We already make a product that can be used for repair as well as plastering an entire ferro armature hull which does not contain any sand, cement or water.

We have Fer-A-Lite hulls that have been inspected after more than two decades of immersion with no signs of deterioration or moisture penetration.

I am trying to just gain a better understanding of this epoxy/cement concept that everyone keeps talking about.

Our base product contains various polyester based fibers and sub components that blend with the polyester resin to achieve the unique properties needed for a completly synthetic mortar, with superior adhesion, flexibility, impact resistance and moisture resistance.

Epoxy does not blend with the polyester based sub components, which tells me I would need to come up with a completely different formulation to gain the same benefits from an epoxy based product that we currently get with the polyester based product.