Nice idea, huh. Not many hits for "concrete" on this forum.

If you use ABS as the skinning and support material (for ABS reinforced concrete) you can cure the object very quickly in a kitchen steamer, and repair the infill with fresh ABS and smooth with acetone.

Whaddya y'all thinking?

I guess a good place to start is a concrete mixer.

Plan is to mix and tumble the additives in water first. That way, you can grind down very hard material (in theory, even diamond dust) to make the smallest gran size.

Then add the right amount of dry cement, finish mixing, pour or inject, and maybe rotorcast or steam to cure the piece. ABS or better if you want steam curing.

Lots of designs out here on Thingiverse, for tumblers, they should be a good starting point. I'm going to make and experiment some more.

[www.thingiverse.com]

Edited 1 time(s). Last edit at 10/27/2016 02:43AM by DragonFire.

Other HUGELY important issues are Safety and environmental safeguards.

Cement and concrete powder dust is classed as an Irritant (so are ABS fumes), affecting the eyes, also the nose, mouth and respiratory systems by breathing. Wet cement and concrete mixes can burn the skin until they are dry.

Most literature recommends gloves, safety goggles and a breathing mask to protect people. That doesn't actually protect the environment.

A more effective system for the small scale experimenter like myself is to work inside an transparent enclosure, via gloves fitted in one side. That way, the dust can't get to my eyes and respiratory system, and I won't be touching it while wet. In the long run, it is cheaper than disposable air masks and gloves, in the long run, and I also have much less cleaning to worry about from dispersed dust and powder.

I was very fortunate in having a friend that didn't want a large fish tank anymore. A cheaper solution is to build a frame, and use transparent flexible plastic to wall it with (polyethylene sheeting is very common even in the poorer parts of the world).

By fitting a vacuum cleaner and filter to the air outlet, and a filter to the air inlet, I can prevent contamination of the environment, recycle the fine dust using appropriate filtes, and also prevent contamination of the concrete mixes from outside sources.

A bit like a clean room, but on a much smaller scale and budget.

If you are experimenting with concrete Hardcore Infill, do take appropriate safety precautions. You and others around you will be healthier for doing so.

Edited 5 time(s). Last edit at 10/28/2016 07:36AM by DragonFire.

Filter and Mesh Types

If you are going to be grading and sorting very small partiles, you need appropriate filters sizes and materials. Both are important to a degree.

Filter materials

You got two basic types of material - organic and inorganic. An example of an inorganic filter is a metal mesh. You can get coarse meshes from building suppliers, if you want finer, try ebay. The USA protects it's steel industry by banning import of these, but I daresay the USA makes lots of its own in stainless steel, as do many developed countries. "Grading mesh" is what you are looking for.

Inorganic meshes are great for sorting out material, but I wouldn't use them on a breathing system. Stainless steel contains Chromium, and while it isn;'t going to contaminate a particular concrete very much, it could theoretically contaminate an individual using the same filter for years on end. The risk is very low (Chromium isn't a problem on it's one, it becomes a carcinogen, Covalent Chromium 6, when it bonds to other compounds). But why take any risk at all?

Examples of organic filters are cotton fabric (available practically everywhere), raw silk (finest but most expensive natural product), carbon fiber mesh (expensive but very hardwearing), and synthetic foam made from organic chemicals. Foam is the cheapest, and is widely used in HEPA filters. There are plenty of other fabrics you can use too, but they all contain dyes, bleaches, and fixing agents. They can be used, but they will add a little contamination to your mixes, in terms of a trace element of the dyes, bleaches etc..

Filter Types

There are different ways to rank a mesh, the most important is, what's the largest grain size that it will pass?

A superfine "silk steel" AWG49 is rated at a particle size of 3.3 microns or so. That's about the smallest I can find easily on eBay.

One other point - a filter can be damaged by material that is harder than the filter. If the material being sifted is harder than the filter material, it can damage the filter, breaking a strand, and leaving a gap for other big particles to pass through.

So treat your filters gently, and they will last.

Foam is usually rated at a particulate size too, for dust. Foam''s big advantage on wet material is that it will quickly soak up the smaller particles and the liquid, leaving the big particles on the outside. A quick squeeze to remove the liquid and smaller particles, a brush off to get the big particles off, and it's job finished. Likewise, cleaning an air filter - very quick with foam.

Do check the foam material, to make sure it isn't itself a health hazard. Talk to the supplier about who made it, in order to get the google the right data sheet for it and check.

Foam has one big advantage, it is very easy to use on damp materils to quickly seperate the wet and non-porous components of a material.

Edited 2 time(s). Last edit at 10/28/2016 07:59AM by DragonFire.