Concrete Boat Cements Its Way To High Speeds

November 11, 2022 by Ryan Flowers 12 Comments

Steel is scarce. Wood is not an option. And you need a boat now. These wartime circumstances drove innovation in all kinds of crazy directions, and one somewhat less crazy direction — concrete boats. As [Peter Sripol] demonstrates in the video below the break, making an RC concrete boat isn’t hard. Making a fast one on the other hand is. But that didn’t stop him from trying, and we think the effort deserves a look.

Starting with a basic displacement style hull, [Peter] and his cohorts experimented with a simple RC boat that worked, but could only move at slow speeds. They turned things up a notch or two and instead modeled their concrete boat after an RC speedboat hull that they had on hand.

The construction methods left a lot to be desired though, and they even tried various wire meshes as rebar, but they proved too heavy. Eventually though, they got a working hull, and had some fun with it. Rather than try to make the hull watertight with a rudder and propeller, they opted for a ducted fan and an airboat style rudder to make what they call the “world’s fastest concrete boat”.

Whether it’s the fastest or not is unconfirmed, but it is fast and actually gets on step fairly nicely. We applaud the exploration of alternative materials and the experimentation with different build methods. If building things with concrete floats your boat, then be sure to check out this concrete pinhole camera.

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A Good, Hard Look At Pre-Stressed Concrete

September 29, 2020 by Kristina Panos 43 Comments

From the looks of the average driveway or sidewalk, it may seem as though concrete is just destined to crack. But if concrete is so prone to cracking, how are we able to use it in so many high-stress applications like bridges and skyscrapers? This question came about while I was researching 3D-printed thermite for an article. Thermite is often used in welding railroad tracks, and I linked a video of fresh tracks being welded that had concrete ties. I knew I had to find out how concrete could be made to withstand the pressure of freight trains.

On its own, concrete is brittle and has no give to it at all. But that doesn’t mean it isn’t strong. Although concrete has good compression strength, the tensile strength is quite poor. Around the late 1800s, someone thought to fortify spans of concrete with steel reinforcing bars, better known as rebar. Steel can stretch, adding steel bars gives the concrete some tensile strength to go along with its compressive strength. Rebar also allows for thinner slabs and other members.

Rebar Only Goes So Far

Parking blocks are meant to be replaced occasionally. Image via Checkers Safety

Rebar or mesh-enforced concrete is good for things like parking lot blocks and roads, but it still fails before it ought to. In fact, it usually has to crack before the rebar can chip in any of its tensile strength.

In high-stress concrete applications like bridges and skyscrapers, it’s terrifically important to avoid deflection — that’s when a concrete member flexes and bends under load. Deflection can cause the modern glass skins to pop off of skyscrapers, among other problems.

A solid, rigid bridge is much nicer to walk, drive, and bicycle on than a bridge that sways in the breeze. But how do you do make a rigid bridge? One solution is to apply stresses to the concrete before it ever bears the load of cars and trucks or a steady schedule of freight trains.

Pre-stressed concrete is like rebar-enforced concrete, but with the added power of tension baked in. By adding stress to the concrete before it goes into service, deflection will be reduced or perhaps eliminated altogether. With the addition of tensile strength, more of the concrete’s own strength is able to come into play.

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Hackaday Podcast 038: Cyberdecks Taking Over, Resin 3D-Printing Vs FDM, Silicone Injection Molding, And The Pickle Fork Fiasco

October 4, 2019 by Mike Szczys 4 Comments

Hackaday Editors Tom Nardi and Mike Szczys comb through their favorite hacks from the past week. We loved Donald Papp’s article on considerations before making the leap from FDM 3D Printers to a resin-based process, and we solidify our thoughts on curing cement in low-gravity. Tom’s working on a Cyberdeck build, and he also found an ancient episode of an earlier and much different version of the Hackaday podcast. We’re impressed with a mostly 3D-printed useless machine, a thermal-insert press that’s also 3D-printed, and the Raspberry-Pi based Sidekick clone that popped up this week. A DIY wire-bending robot is an incredible build, as is the gorgeous wire-routing in a mechanical keyboard, and the filigree work on this playing card press. Plus you need to spend some time getting lost in this one hydrogen-line telescope project.

Take a look at the links below if you want to follow along, and as always tell us what you think about this episode in the comments!

Take a look at the links below if you want to follow along, and as always, tell us what you think about this episode in the comments!

Direct download (60 MB or so.)

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Off-World Cement Tested For The First Time

September 30, 2019 by Tom Nardi 54 Comments

If the current Administration of the United States has their way, humans will return to the surface of the Moon far sooner than many had expected. But even if NASA can’t meet the aggressive timeline they’ve been given by the White House, it seems inevitable that there will be fresh boot prints on the lunar surface within the coming decades. Between commercial operators and international competition, we’re seeing the dawn of a New Space Race, with the ultimate goal being the long-term habitation of our nearest celestial neighbor.

Schmitt's dusty suit while retrieving samples from the Moon — An Apollo astronaut covered in lunar dust

But even with modern technology, it won’t be easy, and it certainly won’t be cheap. While commercial companies such as SpaceX have significantly reduced the cost of delivering payloads to the Moon, we’ll still need every advantage to ensure the economical viability of a lunar outpost. One approach is in situ resource utilization, where instead of transporting everything from Earth, locally sourced materials are used wherever possible. This technique would not only be useful on the Moon, but many believe it will be absolutely necessary if we’re to have any chance of sending a human mission to Mars.

One of the most interesting applications of this concept is the creation of a building material from the lunar regolith. Roughly analogous to soil here on Earth, regolith is a powdery substance made up of grains of rock and micrometeoroid fragments, and contains silicon, calcium, and iron. Mixed with water, or in some proposals sulfur, it’s believed the resulting concrete-like material could be used in much the same way it is here on Earth. Building dwellings in-place with this “lunarcrete” would be faster, cheaper, and easier than building a comparable structure on Earth and transporting it to the lunar surface.

Now, thanks to recent research performed aboard the International Space Station, we have a much better idea of what to expect when those first batches of locally-sourced concrete are mixed up on the Moon or Mars. Of course, like most things related to spaceflight, the reality has proved to be a bit more complex than expected.

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How To Build A Small Metal Furnace At Home

May 4, 2019 by Lewin Day 14 Comments

Casting is a great way to make your own custom metal parts. However, casting requires some manner of furnace capable of generating high enough temperatures to melt the metal in question. Few of us have these just lying around, but never fear. It’s possible to build a basic gas-powered furnace at home, with commonly available materials (Youtube link, embedded below).

This furnace is the work of [Ahmed Ghr], and is as simple a build as they come. The idea is to produce a mold in which to cast concrete to create the furnace. A steel bucket is cut up and used as the outside of the mold, with a pipe inserted in the base to act as a feeder for air and gas. A plastic bucket is then inserted within the steel bucket and held in place with spacers, to create the inner combustion cavity. Concrete is poured in and allowed to set. Once finished, the steel bucket is cut away, and a fire is built over the furnace to melt away the plastic inside. Similar techniques are used to produce the lid, and the furnace is completed.

It’s a build that is executed with the most basic of tools, and should serve as a capable furnace for lower melting point metals at the very least. We’ve seen a lot of cement projects lately, as it turns out. Video after the break.

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Cement Shelves Double As USB Hub

April 20, 2019 by Lewin Day 13 Comments

Some of us are able to get by in life with somewhere between 0 and 1 USB ports. We typically refer to these people as “Mac users”. For the rest of us, too much is never enough, and we find ourselves seeking out expansion cards and hubs and all manner of perverse adapters and dongles. [JackmanWorks] was a man who found himself in need of more connectivity, so he built this beautiful shelf with an integrated 12-port hub.

Material choice is key here, with this build looking resplendent in mahogany and cement. As the core of the build, the USB hub is first disassembled and sealed up to prevent damage from the cement. Hot glue is used to protect the PCB, while electrical tape helps cover the individual ports. The cement is then poured into a form which creates the overarching structure for the shelf, with the USB hub being cast in place. With the cement cured, mahogany boards are then cut and waxed, before installation into the structure. These form the individual shelves which hold phones, hard drives and other USB accessories.

The shelf was designed so that the entire structure is supported through the bottom shelf, which then sits on top of the desktop computer case. It’s an attractive piece, and the weight of the cement construction makes it pleasantly stable in use. It’s rare, but we do occasionally see shelf hacks around these parts. Video after the break.

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Replicating A Victorian Era Console

April 26, 2017 by Adam Fabio 27 Comments

[Dt99jay] lives in a historic Victorian-era district in the UK. Most homes in the area have ornate exterior window dressings with stone consoles holding up heavy stone hood molding.

The window hood molding turned out to be wood — most likely the result of damage repaired after the blitzkrieg bombings of WWII. The 1940’s era work is now rotting away, so it was time for a repair. When the hood was pulled away from the window, disaster struck. One console completely crumbled, while the other lost large chunks of material. The They weren’t solid stone after all, but replacements most likely molded with Coade stone.

There are no ready replacements for consoles like this. [dt99jay] couldn’t just swap them out for modern looking replacements, so he set about replicating the consoles. The remaining console was much too delicate to remove from the building, so [dt99jay] glued the missing pieces back on. He then filled any missing parts and carefully scraped way all the loose paint. Then came the difficult part — making a mold while the console was still mounted on the house.

Room Temperature Vulcanizing (RTV) silicone rubber was carefully applied to the console. The RTV is thick enough to stay on while it dries. After several thick layers of RTV, the console was covered. [Dt99jay] then covered the mold with plaster of Paris bandages to support it. The finished mold was carefully removed from the house, and [dt99jay] filled all the low spots and air bubbles with RTV.

New castings were made using a mixture of cement and playground sand. Once painted, the results matched perfectly. The historic conservation committee was pleased, and the window was once again structurally sound.