Page 40: of Marine Technology Magazine (November 2024)

LANDER LAB #12

Figure 1

A ferrocement anchor is heavy enough to do the job, and cheap enough to not strain the budget.

HOW TO MAKE

FERROCEMENT

ANCHORS

By Kevin Hardy, Global Ocean Design LLC, MTR columnist

Expendable anchors should be dense, cheap, biodegradable, cement, a material that that is mixed with water to create a slurry readily available and scalable. that hardens and binds the other ingredients, called aggregates,

Iron barbells weights are dense, speci? c gravity of 8, are bio- such as sand, gravel, or crushed stone together. An unforeseen degradable, iron is a key nutrient in primary productivity, but shortage of bar bell weights for an upcoming lander deployment not so cheap, about $2/pound. They are readily available and made a new aggregate material seem reasonable: steel stampings.

can be stacked, making them scalable. Necessity being the mother of invention, we hit pretty fast on

Concrete is cheap, environmentally neutral, but with a low a new idea: Concrete doesn’t have the density we prefer, but speci? c gravity of about 2.7. When submerged in seawa- what if we substitute iron stampings for gravel in the mix, while ter, buoyant force subtracts 1 from the 2.7, making the water keeping the sand and Portland cement as the binder. We’ll use weight of the anchors only 63% of their air weight. To bump rebar to tie a chain to, and a 5-gallon plastic bucket as our mold. the water weight up to 100% of the original target weight, the We checked and found scrap iron stampings are available air weight has to be increased 37%. That’s a lot of extra mass to from a number of sheet metal shops around town. We were have to deal with on the deck of a ship or hanging over the side. happy to ? nd the scrap value is only 3-5 cents a pound. We

In Lander Lab 1 (January/February 2022) we mentioned a also found that stainless steel stampings were segregated from hybrid solution, the “Ferrocement Anchor.” Since then, I’ve the common steel because they were worth 6-8 cents a pound. shared this approach with colleagues in the Landerean com- Stainless steel is non-magnetic, which may be a useful proper- munity, here and abroad. ty to have. Ferrocement anchors breakdown faster than com-

Concrete is a composite material made of three things: Portland mon concrete. We’re talking a couple of years. Seawater seeps

Figure 3 Figure 2 Figure 4

Steel stampings replace gravel in The rebar is inserted into the last link Mortar mix is Portland cement and sand. Ferro- ferrocement anchors. of the chain and ? xed by baling wire to cement replaces the gravel with steel stampings.

hold the pieces together.

40 November/December 2024

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