Which material is best for sinking into concrete sidewalk for outdoor use

[melissaa 0]

Hi, I would like to know if PETG is the best material to sink into a concrete sidewalk. The material will be exposed to all of the elements and will be in direct sunlight for most of the day. Also, how long will the material last in these conditions? If this is not the right option, which material will be the best?

[gr5 1,998]

I don't know about UV rays and PETG.  However...

 

I have had no trouble with PLA outdoors in sunlight and rain.  I have a knob that has been outside for about 8 years and still looks like new (near Boston).  Heat is a more serious issue.  It will get soft like clay at about 52C (about 130F).  You can probably reach those temps in direct sunlight.  If it's just for decoration - in other words if a slightly melted plastic has no where to go then maybe its fine?  Although I guess it could stick to people's shoes.  Probably not though.  You can definitely get over 130F in a hot car in the summer and that will indeed make a PLA part slump if it's sitting on the front seat.

 

Anyway, PETG can go a bit hotter (150F I think? I forget) which is good enough for many locations in the world.  Not good enough for UAE or death valley but probably good enough for Georgia.  Probably.

 

First remember this isn't air temp, this is the temp in direct sunlight on the ground.  Also remember that it may bet soft at that temperature but if it isn't under a strong bending load then it is no worse than walking on cold clay (think clay tennis courts).  One inch below the surface of the ground should be fine as well as it won't get that hot down there.

 

If you think it will get above 150F, the next material that has nice texture, look, and colors would be ABS which you can pour boiling water into a cup made from ABS and it's fine.  It doesn't get soft until 99C.  So as long as you don't dip it into a pot of continuously boiling water, you can pour boiling (100C) water into it and the water will cool below 99C in the first second..

 

 

[melissaa 0]

Thank you so much for responding. PLA is the only material I have ever worked with, but maybe ABS would be better because of the heat factor. The filament will be used to decorate a sundial made of pavers. I would not want there to be any chance that the material would be soft to the point of being embedded with little pebbles, dug out, or terribly scratched. I had not thought of it not having anywhere to go. That's a good point. I was worried about how the material and the concrete would expand and contract in the elements, but it doesn't sound like that will be an issue. Thanks again. 

[Smithy 1,135]

I recommend ASA instead of ABS for outdoor usage because ASA is more UV resistent than ABS.

For example a white ABS part will become slightly yellow with the time.

[melissaa 0]

Thank so much for the suggestion. I looked it up and it is supposed to be good for UV resistance and water resistance. It sounds ideal for this project.

[gr5 1,998]

A sundial!!  I hope you use one of those sundial calculators that can be set to your longitude and lattitude for accuracy.

 

I made a sundial at an elementary school where a kid is the gnomon.  They stand on the current month and stick their hand up and the shadow falls on the hour.  Quite accurate.

 

[gr5 1,998]

Here is one such example: https://learningstructures.wordpress.com/2010/05/03/the-human-gnomon-project/

 

If you google "human gnomon sundial" in an image search there are so many different cool ideas.

 

 

[gr5 1,998]

Wow.  Expansion.  Didn't think of that.  I guess I'd to an experiment with a paver or a few and some 3d printed plastic and heat up the pavers with a hair dryer or something to around 120F and then let it cool to outdoor temps and repeat a few times.

 

If the pavers have slots for the markings you could maybe skip the 3d printing and melt something right into the slots in the pavers?  I don't know if that would work.

 

You may have some trouble gettings ASA to stick well.  If so come back to the forum and ask about it.  You just have to know the tricks of how to deal with each problem you run across.

[GregValiant 980]

OK @gr5, You made me look up gnomon and I'll buy that.  But your claim that kids can stand in one place long enough to cast a shadow is a bit hard to chew.

 

What goes around comes around though.  Both of my boys are chasing kids of their own.  The wife and I laugh and laugh and pass out more candy.  Then we go home while we can still see the sundial.

[melissaa 0]

Wow, a whole team of mathematicians is needed to develop the whole thing. Atleast, we have a start on the materials.