I need to make a mooring.

[Scott T-Bird]

So I got currious and did some digging... found this interesting article.

Cement & Concrete FAQ - Portland Cement Association

Your basic cement and concrete questions answered by qualified experts.

www.cement.org

It does state that iron corrosion is a major issue but it also says that if done right...


Concrete and the Passive Layer
Although steel’s natural tendency is to undergo corrosion reactions, the alkaline environment of concrete (pH of 12 to 13) provides steel with corrosion protection. At the high pH, a thin oxide layer forms on the steel and prevents metal atoms from dissolving. This passive film does not actually stop corrosion; it reduces the corrosion rate to an insignificant level. For steel in concrete, the passive corrosion rate is typically 0.1 µm per year. Without the passive film, the steel would corrode at rates at least 1,000 times higher (ACI222 2001).

Ohhhhh .... that was written by PCA. Now I understand! Just ignore all of the physical and practical evidence! Go with the obscure chemist's explanation! All you have to do is make perfect concrete! It's not the fault of concrete that nobody can get it exactly right! Can't those ignorant contractors and engineers ever do anything right?!?

 

[rgranger]

Sure, steel rebar that is encased in concrete that is well-protected from moisture will not corrode for a long time. It's misleading to state that concrete inhibits rust in embedded rebar. Clearly, based on the billions of dollars spent on renovation and the catastrophic failure of concrete when neglected it is a travesty to even suggest that rebar does not corrode when embedded in concrete. Spalled concrete all across this nation is the leading cause for the degradation of infrastructure. Concrete doesn't spall until the corroded steel embedded within loosens the concrete. Carbonation - the process by which the degradation of concrete leads to the corrosion of rebar.

The article clearly says that it is the pH of concrete that inhibits the rusting. It is not missleading to say concrete inhibits rust formation.

And why are we talking about bridges? A bridge should last a 100 years ... we are talking about a homemade mooring....something that should be dived on annualy and inspected.

The article also indicates that much of the iron-bridge failures we are seeing are due to the types of salts used to de-ice the bridges in winter months but I did not read that carefully enough....

 

[Scott T-Bird]

The article clearly says that it is the pH of concrete that inhibits the rusting. It is not missleading to say concrete inhibits rust formation.

It is misleading to suggest that the pH is protecting steel when the overwhelming reaction is carbonation that leads to the corrosion of steel. The practical evidence is overwhelming. Sure, the pH works as a lab experiment ...

The reinforcement is protected by the alkaline condition caused by the hydrated cement paste. This is neutralized by the carbonation allowing the corrosion in the presence of oxygen and moisture.

I'll make an analogy ... Say after a swimmer dies from hypothermia after being in really cold water for 2 hours. You would say ... he didn't die from hypothermia because his core body temperature protected him for at least 5 minutes after he fell in the water!

Sorry .... I'm like a dog with a bone over this!

Aside from that, for reasons stated, a concrete block in this circumstance is just a poor choice. Probably the worst choice. He wants to make something light enough to manhandle himself ... recipe for disaster! There isn't a cheap solution unless he wants to try a manufactured anchor and set it for a permanent anchor. That would be far better, as poor a choice that would be, than dropping a 300 pound concrete block that's going to skate across the bottom.

 

[nothingventured]

We have used Iron Rebar in Concrete for years.
The Rebar never corrodes inside the cured Cement.

For this reason


Back on topic..

1) Mould your mooring block with pyramid shape [less drag and tipping]
2) Bend and wire connect Standard Rebar about 2 layers separated by 3-6 inches-[ 2" off bottom of block going upward for next layer]
3) Weight of Block should be sized per Boat size and buoyancy per above comments.
4) Install large Stainless Eye bolt from top thru bottom of Pyramid

Jim...

PS: Just Read above post. Building bridges that take Vibrational loads is much different
Static loads found in a Grand Hotel built in the 1920 had ZERO Rebar corrosion on it Structural Columns... Case Closed

Yes I thought of using the pyramid shape, and using concrete or mortar only for the glue to hold bits of iron or granite. ignoring the concrete exists in it, I still wonder what weight I should go for. I don't have a crane to lift it in so I am tempted to do several smaller ones that are struck together.

 

[PaulK]

Perhaps the best idea would be to ask around and see what other people are using there for boats in your size range. What works for them should work for you. It also avoids having to re-invent the wheel through a process of trial and error that might cost you your boat as well as all the time and effort involved in making and setting mickey-mouse "anchors" .

 

[Scott T-Bird]

Yes I thought of using the pyramid shape, and using concrete or mortar only for the glue to hold bits of iron or granite. ignoring the concrete exists in it, I still wonder what weight I should go for. I don't have a crane to lift it in so I am tempted to do several smaller ones that are struck together.

Structural concrete has bits of iron and rock in it, it doesn't change the fact that it still weighs 150 pcf on land. Your 300 pound block is still going to weigh 175 pounds in the water. Your pyramid shape will probably do you no good on the bottom. It's not going to facilitate holding. Why would you want less drag ... you want more drag. If the pyramid is sitting on hard sand or rock, it is still going to skate like a hockey puck on ice.

The best advice, as PaulK says, is do not re-invent an anchor. Find out what is holding down the boats in your area and do that.

 

[rpell1@msn.com]

Here in Sheepshead Bay, Brooklyn, NY, mooring space is a premium. The Coastguard set a minimum for this mooring field and it seems to work very well
. Two 150 lb. mushroom anchors with 35' of 1/2" chain on each, spread at 20' apart. Depth at high tide is 17' maximum. This is for boats up to 34'. All rigs must be inspected every 3 years. Over this, the minimum goes to 250 lbs., but the chain remains the same. Over the past 30 years, there have been, maybe, 10 boats that dragged their anchors. Have you spoken to any moored boat owners about what they are using?