Hermit
Active member
This thread was much more interesting when it was about the sunk boat in Brixham.
Gaff schooner sunk in Brixham
- Thread starter Gary Fox
- Start date
Stemar
Well-known member
Thanks for that. I always thought concrete was mostly CaCO4. If it's unstable in seawater, what do they do when building bridge pillars?
AntarcticPilot
Well-known member
Geologists have a different view of "unstable" to most folk. But Alcatraz was abandoned because salt water eroded the concrete.
D
Deleted member 36384
Guest
Not being flippant, they add stabilizers to the slurry, plus other additives to enhance the properties. There are also many types of cement powders. For example, in the oilfield we have Class A, B, C, D, E, F, G, H and Poznix, Pozmix 140 cements. A catalogue of additives shows over 100 different additives that control fluid loss when the cement sets, plus accelerators and retarders for use in saltwater. The retarder stops the slurry setting fast in saltwater and achieving poor strength. Alcatraz slurry design would have been unsophisticated by today’s standards. I believe the civil engineering slurry designs use different designations for the bulk powders and chemicals.
JumbleDuck
Well-known member
You've intrigued me enough to have a look. It appears that set cement doesn't actually contain any calcium carbonate. From Hydration:
Hardened paste consists of the following:
Ettringite (hydrous calcium aluminium sulfate - JD): 15 to 20%
Calcium silicate hydrates, CSH : 50 to 60%
Calcium hydroxide (lime): 20 to 25%
Voids : 5 to 6% (in the form of capillary voids and entrapped and entrained air)
Ettringite (hydrous calcium aluminium sulfate - JD): 15 to 20%
Calcium silicate hydrates, CSH : 50 to 60%
Calcium hydroxide (lime): 20 to 25%
Voids : 5 to 6% (in the form of capillary voids and entrapped and entrained air)
Mudisox
Well-known member
I have found thread drift on this site but this surely wins the prize. 
D
Deleted member 36384
Guest
I have found thread drift on this site but this surely wins the prize.
It certainly does, writing about thread drift, when everyone else is writing about cement boats and salvage implications.
Mark-1
Well-known member
I have found thread drift on this site but this surely wins the prize.
TBH going from a sunk concrete boat to how concrete behaves in salt water is pretty much on topic.
Wansworth
Well-known member
I have to lay a concrete path.....
AntarcticPilot
Well-known member
I think that the point is that although Chalk or limestone is a major ingredient in making concrete, the result is not Calcite or Aragonite, but a mixture of low-temperature silicates, and so is quite different from the skeletons of reef-forming organisms. As you say, additives are used to stabilize it in various environments, but even so, in the long run, concrete is unstable and will deteriorate - even though it may take a very long time by human standards; after all, Roman concrete is still going strong in many places! But the use of concrete is strongly deprecated in sensitive environments, and where it has been used, the goal is to remove it. One of my projects was to create a geographic database of field equipment around the BAS base at Rothera in Antarctica, and anything made of concrete was included with the goal of removing it as soon as its original purpose was fulfilled.
dgadee
Well-known member
I have found thread drift on this site but this surely wins the prize.
Hardly. Sunk boats, abandoned boats. Where's the drift there?
trevbouy
Active member
Back on topic.
Well gents we have another ! Not a sinking but an abandonment.
I saw this in the harbour two years ago but thought it was still fishing but apperently not.
The MV Accumulate has been seized, put up for auction but I suspect it will be left for the harbour authorities to dispose of.
Well gents we have another ! Not a sinking but an abandonment.
I saw this in the harbour two years ago but thought it was still fishing but apperently not.
The MV Accumulate has been seized, put up for auction but I suspect it will be left for the harbour authorities to dispose of.
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trevbouy
Active member
I also looked at Sea Beast today. She has been tied up from many points, not least the masts held from keeling over. You can see the ropes in the middle of the pics plus the bollards they are moored to.
There is also an automatic bilge pump plugged into the shore supply cabinet. (The thin yellow cable bottom right)
There is also an automatic bilge pump plugged into the shore supply cabinet. (The thin yellow cable bottom right)
Rappey
Well-known member
The boat is not cast from concrete though. It's usually sulphate resisting cement which is a lot more resistant to aggressive environments and mixed with very fine washed sand at a 1:1 ratio, making it impervious to water. Liming can occur producing osmosis type bubbles under the paint but it's due to the sand not being clean enough
Surely if it leeched it's contents the paint would blister like mad.
From visiting Alcatraz I was under the impression it was the steel rusting blowing off the concrete.
Surely if it leeched it's contents the paint would blister like mad.
From visiting Alcatraz I was under the impression it was the steel rusting blowing off the concrete.
Rappey
Well-known member
Next time your there can you do a walk through ? ?
penfold
Well-known member
pvb
Well-known member
Interesting!
Gary Fox
N/A
Thanks. What a shambles.
Gary Fox
N/A
Yes and if he finds my head torch, it's ok, I've bought another since then.
dgadee
Well-known member
And you 'liked' the thread drift criticism in post #281! Shame on you, Mr Fox.