1.0 Introduction“Only you can find a ship in the middle of the Canadian Rocky Mountains!,” said my wife while we enjoyed our vacation. Resting at the bottom of Lake Patricia, nestled in the remote mountain town of Jasper, Canada, lay the remains of project Habbakuk. The adventurous idea to create a giant aircraft carrier from ice. Started during World War II, the desperation of war asked for creative solutions. At first, ice seemed like a ridiculous building material, except for one factor. Ice comes free. At least, that was the initial premise. Further research revealed ways to enhance ice, including the development of Pykrete, a unique ice composite. Project Habbakuk gave birth to one of the most unique material composites we know: Pykrete.Figure 1-1: Project Habbakuk https://youtu.be/CB0wE--NJ3E2.0 Why This MattersProject Habbakuk represents more than a crazy wartime project. It became a serious study in pursuing alternative building materials. The results from Habbakuk inform and influence our future hunt for better structures. Consider the future of industrial development. We focus on ecologically friendly construction. How to reduce the carbon footprint, while increasing performance? Although I don’t have an answer to this question, I start by studying the past. And from the distant to recent history, several trends seemed obvious:- Technology is often restricted by the materials available. Better materials mean better ships.- Current advancements in structural materials focus on composites. Blending two different materials to form a superior combination. Examples include:- Fiberglass and epoxy resin for yacht construction- Concrete: a composite of cement, aggregate, and sand- We need composite materials made from sustainable sources- We need composite materials that are economically recyclable. Modern composites deliver impressive performance, but they require very intensive processing to source the materials. And we can’t recycle them. Concrete buildings, fiberglass boats. Neither easily separate into their components. I occasionally see efforts to develop a recycling process, but it always involves large energy input or chemically intensive process. Our modern world builds thousands of composite products, made with no way to recycle them. Nothing proved economically affordable. The best approach so far: grind it up and hope someone finds a use for the rubble.Figure 2-1: Testing Site: Frozen Lake in Jasper Considering this problem of sustainable composites, now look at Pykrete. It was a new composite material, based on a combination of saw dust and frozen water. To build it, you only need wood and water, both eminently sustainable sources. And to recycle the composite, just stop cooling it. The water naturally melts, leaving a pile of wood pulp to decompose. By all the requirements of current material research, Pykrete gets high marks. But we don’t have Pykrete ships. What went wrong? What can we learn from Pykrete to guide us in future materials research?3.0 PykreteProject Habbakuk originally intended to use simple blocks of ice. Maybe even icebergs, cut loose and fitted with propulsion. But initial tests quickly revealed a host of problems with this, including rapid melting of the ice. Enter Geoffrey Pyke, who developed the idea to blend ice and wood chips together. After some experimentation, they hit on the right mixture.“. . . a 14-percent solution had the consistency of wet cement and the strength of concrete when frozen. Pulp worked better than sawdust because the ragged fibres of the pulp created a better interlocking bond than the clean cuts in sawdust.”As strong as concrete. Sounds promising, right? In fact, Lord Louis Mountbatten, one of the principal champions of the project, demonstrated the strength of Pykrete by proving it bulletproof. At a conference of high ranking leaders, he shot a revolver at a block of plain ice, which shattered. No surprise. He then shot at a block of Pykrete, and the bullet ricocheted of the block, passing through the pant leg of a nearby officer. Pykrete had the potential to be more than a mere toy.Not only stronger, Pykrete also took longer to melt. The Discovery show Mythbusters demonstrated this admirably by comparing the melting time of a traditional block of ice vs Pykrete. (Figure 3‑1) After 3 hours, the regular ice block had nearly melted. The Pykrete block showed little degradation. https://www.youtube.com/watch?v=UMKis4FPykwFigure 3‑1: Pykrete Melting Comparison Pykrete still required active refrigeration to use it as a building material. But it showed great promise, and the developers hoped this cheap and easy building material justified the effort of refrigeration.3.1 Pykrete Composite DevelopmentOne of my favorite examples for Pykrete came years later, when the Discovery show Mythbusters made an ice boat, using a modified version of Pykrete using newspapers instead of saw dust. (Figure 3‑2) This TV entertainment unknowingly researched enhancement of Pykrete as a composite material.https://youtu.be/eCszy7mQye8Figure 3‑2: Mythbusters Pykrete Boat Most composite materials consist of two basic parts:- A strong fiber of some type.- A matrix (the glue) which starts as a liquid and then transforms into a solid, either as a phase change or chemical change.The original version of Pykrete started with wood chips. And then they discovered wood pulp works better. The smaller fibers allow more surface area, for a better bond between the wood fibers and the ice matrix. The next step up, use continuous fibers, woven together. The longer fiber length creates more contact area between fibers. This allows better stress transfer from one fiber, through the matrix of ice, to the next wooden fiber. Paper forms from creating wood pulp and pressing it together. When the Mythbusters used newspapers for their Pykrete, they progressed closed to using continuous fibers. This is the evolution of creating a better composite material.Modern composites followed the same development cycle. Many of the improvements came from creating better fibers for better stress transfer. This shows the hidden insight from Pykrete. If you immediately think “ice”, you have the wrong idea. That biases us and focuses on the weak matrix. Think of Pykrete as a cutting edge composite material, and we see that it closely follows the development of other industrial composites. In fact, one report by Mr. Pyke showed mechanical properties that surpassed concrete. (Table 3‑1)Table 3‑1: Comparative Properties of Pykrete Mechanical PropertiesIceConcretePykreteCrushing Strength 3.44717.2407.584Tensile Strength 1.1031.7244.826Density 9102500980In terms of pure science, Pykrete had the potential of a modern industrial building material.4.0 The Problem of CreepPykrete wasn’t perfect. New building materials depend on more than pure strength. Pykrete faced a major problem with creep. Apply a steady pressure to a Pykrete block, and it slowly (over several weeks) shifts, driven by the pressure. Under a steady load, Pykrete had trouble holding its shape. Creep happens with other materials as well, usually when they approach their melting temperature. And the construction of project Habbakuk hovered very close to the melting point of Pykrete. The researchers found two possible solutions to prevent creep.“Although pykrete was mechanically strong, like pure ice it would slowly deform under constant pressure, and since the bergship would be hollow, its walls could creep inwards unless they were reinforced by some kind of internal skeleton.” . . . “With spruce pulp, creep would stop after an initial period of sagging over a few weeks, but only if the pykrete temperature was kept below 5°F (-15°C).” 5.0 What Went WrongThe science was sound. We had a few challenges, but these were surmountable. What went wrong? First, the scale of the project became too large. They didn’t want a normal ship made from ice. They wanted a super carrier, with a 9 m (30 ft) thick hull completely impervious to torpedoes! The ship had a length of 610 m (2000 ft), 26x bigger than the largest passenger ship at the time. It required 20 motors just to keep the ice cold, and another 30,000 horsepower to limp along at a measly speed of 7 knots. Building an untested ship at this scale, in war time, when supplies were limited. Blatantly ridiculous! But that speaks to the design, not to the failing of Pykrete. For that, we look to the human factor. Frail, temperamental humans. The Pykrete worked fine, provided we cooled the ship to -15°C. But humans don’t like the cold. How do you keep the humans warm and the ship cold? Insulation can only do so much. This showed the first failing as a material. Your materials need to work within the limits of human tolerance. Or you need to remove the humans. That wasn’t an option at the time. The final failing of Pykrete came from the environment. They constructed a scale model of Habbakuk in Lake Patricia. (Figure 5‑1) This is how Jasper, Canada ties into the story. Nicknamed the “boathouse”, this test model did not use Pykrete, only normal ice. They studied building techniques for working with ice. But the boathouse still included a refrigeration plant, reinforcing beams, and all the major elements that would go into the full scale ship. It was a functional test. Can you build a watertight hull with frozen water?Figure 5-1: Scale Model Constructed in Jasper It leaked! Even with the refrigeration, small sections of the ice hull melted. And you only need a small hole for water to flood the ship. Even Pykrete needed strong refrigeration. This showed that, for a ship, refrigeration needed to go beyond general cooling. We required a reliable freezing temperature, held constant throughout every point of the ship. Any hot spot. Any deviation resulted in leaks. We set our best refrigeration technology against nature. And nature proved the more tenacious. This gave the second lesson from Pykrete. When designing a building material, it needs to naturally stay in a stable state for the expected temperature range. We can’t depend on active refrigeration, because nature always wins.6.0 ConclusionIn the end, project Habbakuk never made it past testing. And Pykrete required too many compromises for a practical ship design. But these extreme examples help us to better evaluate mainstream material science. The lessons learned from Pykrete apply to any modern material. This illustrates the prudent questions which narrow our search for new materials:- Composite materials show massive potential.- Any material needs to work within human tolerances.- Don’t fight against nature. Nature always wins.Pykrete didn’t work out. But now we know what to look for in the next wonder material.6.1 The End of Pykrete?I doubt Pykrete will ever see use here on Earth. But sometimes, we just need the right environment for a great building material. Mankind currently seeks methods to build research bases on other planets, using in-situ resources. Maybe we can build a Pykrete protective dome, using resources found on the planets. Places like the Moon, Mars, Europa. These planets exist well below the freezing temperature of water. Earth was too warm for Pykrete, but it might be ideal for other planets.7.0 ReferencesL. Cross, Code Name Habbakuk: A Secret Ship Made of Ice, Vancouver, CA: Heritage Publishing House, 2012.Discovery, "Mythbusters - Pie-Crete," YouTube, 27 Apr 2009. . Available: https://www.youtube.com/watch?v=UMKis4FPykw. .YouTube Creator, "Mythbusters - Newspaper Boat," YouTube, 16 Apr 2009. . Available: https://youtu.be/eCszy7mQye8. .Wikipedia Authors, "Pykrete," Wikipedia, 13 Jan 2023. . Available: https://en.wikipedia.org/wiki/Pykrete. ."Pykrete - Experimental Ice Ships in the Rockies," Combined Operations, . Available: https://www.combinedops.com/Pykrete.htm. .RealLifeLore, "The Insane Plan to Build an Aircraft Carrier Out of Ice," YouTube, 23 Mar 2019. . Available: https://www.youtube.com/watch?v=CF9af8AtxLY. .Wikipedia Authors, "Scale model of the European Moon Village concept," Wikimedia Commons, 24 Feb 2019. . Available: https://commons.wikimedia.org/wiki/File:Scale_model_of_the_European_Moon_Village_concept.jpg. .
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