As a hypothetical assume you need to construct, assemble and/or purchase and bury a cubic meter sized time capsule in a spot somewhere in the mid-Atlantic region of the US. The items in the capsule will need to be recovered 1000 years hence dry and intact so the capsule needs to be sealed and secure in earth that is occasionally subject being waterlogged and freezing and thawing.
You will bury it 2 meters deep in the ground. $1000 is all the money you have to do this. You have one month to make this happen. Assume you will have digging access to the site 1000 years hence.
Reinforced concrete. Stainless steel mesh and rebar reinforcement, The contents would be in a heavy polypropylene container, then the whole thing coated with hard pitch. There’s no door, it has to be broken into 1000 years from now.
Yeah, some sort of inner polymer capsule (I was going to suggest epoxy GRP) encased in concrete, encased in something else waterproof - soldered lead sheeting maybe.
Make an inner box of copper or lead sheet and solder it closed after packing the contents. Maybe polypropylene - it can be hot air welded for a total seal. Then encase in concrete - maybe use stainless steel rod for rebar. In the last 10 years metal “micro-rebar”, carbon fiber, and other polymer fiber reinforcement fillers have been developed that could be mixed into the concrete.
You probably want to consider what you enemies are are. Over 1000 years you need to plan for unexpected long term ones.
Clearly number one is water. Over 100 years water can do untold damage, and can find a way past many apparently impermeable barriers. Other chemical attack probably comes next. This is where you do need to be careful. Oxygen should be excluded, and you need to be sure that nothing in your containment design can break down or leach anything that can itself cause damage. 1000 yeras is a long time. Processes that are essentially imperceptible over decades can have a devastating effect when given that sort of time.
Beware of polymer materials that include plasticisers or other potentially unstable components. Pure polyethylene is probably a good component in a barrier system. But it is permeable to oxygen, so you will want additional barriers. Since it is going to be buried you are not worried about UV degradation. However over 1000 years it isn’t impossible that microbial attack could become an issue. You want to ensure that even a polyethylene container is itself kept dry.
Concrete is good to embed it all in. Clearly steel rebar is out. Even many stainless steels could be a worry over 1000 years. Without the ability to recreate the chromium oxide barrier, SS isn’t nearly as corrosion resistant as you may hope. A fibre reinforced concrete may actually be a better bet. Fibreglass might be a good choice.
Off the top of my head:
Brazed copper airtight inner box. Outside that polyethylene box, hot air welded. Outside that, soldered lead box. I like the idea of pitch. Coat that in pitch. Put it all inside a concrete cube reinforced with fibreglass.
Yeah…and the contents should be considered such that they don’t self-destruct due to entrapped moisture, acid, or not be made of materials that degrade spontaneously.
Also, pitch is NOT such a great material for encapsulation. It was tried in the 1920’s to encapsulate radio components and now is found cracked and possibly a source of corrosion.
Fiberglass is a good idea, and will save money. He’s only got $1000, a metal interior box is going to chew up a lot of money. I’m not a pitch expert, but I believe some variety will hold up considerably longer than 1000 years.
Rebar in concrete is IMO totally not needed in this case. As a matter of fact, its just a metal that will eventually corrode/oxidize, expand, and be the CAUSE of the concrete cracking.
Or in other words it is NOT needed and will ONLY add to the problem
You’ll want to design your inner container so you can pressurize it with ~2 atm of dry nitrogen instead of leaving it full of air. Oxygen is antithetical to long-term chemical stability. Ideally you’d subject the materials to several “washings” with dry nitrogen over a span of months before sealing the inner container in the outer container.
As **billfish678 **said, rebar is all about giving concrete more tensile strength. This isn’t a concern in a one meter object subject only to compression & mild shear.
I’d also be leery of adding fibrous stuff hoping to improve the concrete’s toughness. e.g. polyethylene meshwork, carbon fibers, etc. It’d be easy to include something with an as yet unknown structural half life of 500 years which ends up cracking the concrete or dissolving to nothingness leaving a network of micro voids to facilitate water intrusion.
My question for the OP is how he intends for the people 1000 years hence to know the darn thing is down there and it’s time for them to dig it up? It does no good to create a truly impervious time capsule that’s still undiscovered and hence unrecovered when the Sun finally boils the earth’s crust to vapor.
Given the tight budget and timeframe, I’d look at something ready-made for the container. Something like a plastic or concrete cistern, dry well, septic tank, fuel storage tank or burial vault. All are designed to be underground, but some of them are not sealed. So you’d need to plug up the holes and you still might want to coat the container with pitch, as suggested above.
Note the use of you in both sentences. He obviously has a time machine that will not permit him to carry everything he thinks he will need at his destination.
I’d use one of those big concrete round sections that they make manholes access from. Have it delivered and slid into a big, predug hole, standing on it’s end. Fill to create a concrete floor a foot thick, then scare up something to top it with. Make sure you dig the hole deep enough to be still have 8’ of soil on top!
Either the depth it is buried at needs to be ALWAYS frozen (probably the best actually) or the depth it is buried at needs to NEVER be frozen (probably more likely given the local).
Freeze/thaw cycles are what tears things up long term.
A 1000 gallon septic tank will cost you around $1,000, but that’s about 4 m[sup]3[/sup] … so say $500 for a 1 m[sup]3[/sup] special made for 1000 year burial.
If it won’t be disturbed, $20 for a shovel and a few days digging. $200 for Argon and flood the container just before you seal it. I think you’re fine with a few weeks in your pocket.
Concrete would be good if the container was subject to back hoe hits … but if a back hoe hits it, they’ll be digging it up anyway and the cause is lost … bury it in a National Park at night.
