[Tanada]

Quality concrete mixed from the right materials is such a durable product that it is worth the extra cost to ship in the aggregates rather then use lessor materials and have a product prone to failure at first stress. Look at the earthquake resistance of reinforced concrete structures vs. brick and block construction.

True for purely masonry structures, however when I was observing the construction of the new dorm at BGSU as I drove past for an appointment I noticed the masons were including mesh reinforcing between at least some courses and tying the reinforcing mesh into the wood frame structural members. Funny what you can see when stuck at a stop light waiting for university students to get out of the crosswalk already instead of dawdling along.

I imagine if you were using manufactured sandstone blocks putting layers of wire mesh between courses would go some way toward earthquake survivability though I have no idea how far an improvement it actually is. Code: Reinforced Masonry

Link 2

[Newfie]

One of the very few exports left to SOME Caribbean islands is sand and some rock. The Montserrat earthquake removed all economic activity, but gave the island an excess of sand, which they are exporting.

Maria’s torrential rains washed lots of ash down some rivers, which is being excavated and exported. So I guess some volcanic ash works as a good concrete mix.

[vtsnowedin]

One of the very few exports left to SOME Caribbean islands is sand and some rock. The Montserrat earthquake removed all economic activity, but gave the island an excess of sand, which they are exporting.

Maria’s torrential rains washed lots of ash down some rivers, which is being excavated and exported. So I guess some volcanic ash works as a good concrete mix.

Fly ash and I presume the volcanic ash works in place of it is now a standard admixture in concrete replacing a portion of the Portland cement and improving both work-ability while placing it and early and ultimate strength.

[Tanada]

One of the very few exports left to SOME Caribbean islands is sand and some rock. The Montserrat earthquake removed all economic activity, but gave the island an excess of sand, which they are exporting.

Maria’s torrential rains washed lots of ash down some rivers, which is being excavated and exported. So I guess some volcanic ash works as a good concrete mix.

Roman Empire concrete was a mixture of mortar aggregate and volcanic ash. It is a hydraulic cement that will harden even under water and incredibly tough with many examples still here 2000+/- years later.

The Portland cement invented in England in the 19th century is inferior in some ways but if you add volcanic ask you can get an improved modern product.

[Subjectivist]

Why sand shortage is a big problem

Saudi Arabia has lots of sand. That should be useful for a part of the world with a penchant for constructing ever taller buildings and ever more chic resorts on reclaimed land fanning out into the Arabian Gulf.

Unfortunately, it is the wrong sort of sand.

The Rub al Khali desert, whose undulating dunes inspired both Lawrence of Arabia and Wilfred Thesiger, is composed of grains too small, too round and too smooth to be much use for construction; you might so well make bricks out of icing sugar.

Hence the irony of Gulf countries importing sand from Australia and the popularity of dredging up marine sand to create artificial islands, among other uses.

Sand shortages, and the resultant environmental toll, have long been predicted.

Vietnam, a country where pristine palm-fringed beaches offer welcome rest and recuperation, has said it will fall short this year.

Consultancy Kearney highlighted a shortage of global sand – again, the “right” type of sand – as one of its top calls last year.

Still, the pandemic might just prove a respite. Several projects, from infrastructure to home building, have been mothballed.

Others look anachronistic: take Hong Kong’s third runway, planned at a time when there were more planes in the sky than on the ground.

Unfortunately for marine life and sand bulls, the absence of cheap sand substitutes allied to humankind’s love of follies suggests that any reprieve will be temporary.

https://www.afr.com/companies/infrastru ... 809-p55k05

[sparky]

.
All cement harden under water , cool and wet promote the growth of the latice cristals
to test the quality of cement batches samples cubes are made and kept in bath of water at 15 Dg C for 21 days
then they are tested for crushing and shearing
in construction site if it's too hot , wet hessian cloth is put on the concrete and watered regularly
when building very large structure , like dams or great building foundation care is taken not to pile up too much concrete at once
the hardening is an exothermic reaction and the middle of the pile could overheat , weakening the structure

the worst for cement is dry and salty

[Tanada]

.
All cement harden under water , cool and wet promote the growth of the latice cristals
to test the quality of cement batches samples cubes are made and kept in bath of water at 15 Dg C for 21 days
then they are tested for crushing and shearing
in construction site if it's too hot , wet hessian cloth is put on the concrete and watered regularly
when building very large structure , like dams or great building foundation care is taken not to pile up too much concrete at once
the hardening is an exothermic reaction and the middle of the pile could overheat , weakening the structure

the worst for cement is dry and salty

Having worked on a few construction projects in Michigan in my younger days I can tell you that is NOT how cement was/is tested there. The cement batch being used for the project would have a sample scooped out into a standard plastic form cylinder of about 1 liter volume with the date written on the outside of the form in marker or grease pencil. The form was then set aside and allowed to dry in ambient air for however long it took the state testing agency to request the sample for review. About half the time the state never got around to picking up the cylinders so they were left in a storage area against future request. If the cement/concrete contractor had a good reputation the state usually wouldn't bother doing the test unless some fault developed at a later date.

[vtsnowedin]

Well in my 44 years of inspecting construction work in New Hampshire as a certified testing technician I can say they don't do it that way. . Any placement involving a full load or more of concrete has a sample or samples taken by the ASTM approved method which are tested for temperature, slump, air content, and unit weight. Then cylinder molds are carefully filled and consolidated by rodding then stored in a cooler or water chest while they set up and become strong enough for transport (at least a day) then they are taken to the state DOT lab where they are stored in a moist room kept at 100 percent humidity until they are 28 days old . Then they are placed in a press and crushed to failure to determine the compressive strength of the sample. Extra cylinders are usually taken for 3 or 7 day tests to determine if the concrete has reached 80 percent of design strength (to allow early form stripping). It is not unusual for a bridge project to have over 500 test cylinders made and broken over the course of the project. I have not had a cylinder fail in decades as quality control practices are now so tight it is unlikely but no slacking off of testing has been allowed.
Concrete placements are indeed kept moist with burlap , plastic and even complete sprinkler systems for decks and even such superficial things as a sidewalk will get sprayed with a curing compound that seals the moisture inside the concrete. Back in the thirties mega projects like Hoover Dam had water pipes placed inside the concrete so the circulating water in them could draw the heat out of the curing concrete allowing faster construction.

[sparky]

.
The tests I describe were performed at a large cement manufacturing plant from the raw grind coming out off the clinker ball mills

I still have nightmare of the clay addition weigh scale feeder getting gummy on wet days
the other additives were fly ashes and iron ore which were not a particular problem

[vtsnowedin]

.
The tests I describe were performed at a large cement manufacturing plant from the raw grind coming out off the clinker ball mills

I still have nightmare of the clay addition weigh scale feeder getting gummy on wet days
the other additives were fly ashes and iron ore which were not a particular problem

That would be the quality control process of the cement production itself. I was testing the finished mix of cement plus fly ash, sand and stone, water and admixtures for air entrainment etc. It is pretty common today to get concrete with seven percent entrained air weighing 150 pounds per cubic foot having a 28 day compressive strength of over 6000psi. In fact in some cases I think they go to far resulting in a strong but brittle concrete more prone to cracking in service.

[sparky]

.Thanks to the answers on this point
the basic idea remain than the strength of wet concrete is not impeded ,
getting concrete to set solidly under sea water might be an issue

[vtsnowedin]

.Thanks to the answers on this point
the basic idea remain than the strength of wet concrete is not impeded ,
getting concrete to set solidly under sea water might be an issue

Actually no. I placement under sea water would be done so only the very first concrete placed would be exposed to the water and the rest pumped below it filling the form or cofferdam floating the first placed upward as the later volume was pumped below it through a pump hose or tremie. They stick the pump hose right down to the bottom and start pumping so a bubble of concrete grows around the hose end and as long as they don't pull the hose out of the bubble you get a solid mass of concrete that only the very top surface has ever been exposed to the surrounding water. Kind of like blowing bubbles with bubble gum only instead of your breath making the bubble bigger it is the following concrete.