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Is this a homework or Class Question?

Kind Regards....

It's heavy.

Its hard to work by hand.

It breaks into smaller pieces when hit with a heavy object.

The dust doesn't taste nice.

It doesn't float.

Did I mention it is heavy.

It doesn't taste all that bad, i have had worse. Plus it works as a time release acid neutralizer for acid indigestion. Also it is a good at partially neutralizing Acid spills. Exposure can be a little hard on the skin, but no worse than conc. sulf acid or NaOH. It is a source of calcium, magnesium and silica, good for strong bones. It is a major source of green house gases, so i guess that is a demerit if you live near the ocean on a bay, or more equitorial of about 40 degrees (it might be a benefit if you live inland a little bit and north/south of 40 degrees). It is a good weed control measure. probably many other things too. Is this a homework question or a take home exam.

Demerits of concrete as an engineering material!

Consider concrete in tension. (It's no good!)

Consider it's failure symptoms. (Sudden and catastrophic failure)

Consider the manufacture of the raw cement. (Energy hungry process)

Cement dust is hazardous. (So drilling/cutting etc require protective equipment.)

Once it's set it cannot be re-shaped. (See separate threads about the refrigeration plant with a leaking pipe somewhere under concrete slab, garage floors with sinking slabs, houses with water oozing up through the carpet and the list goes on...)

Formwork is usually required. (Cost of manufacture and disposal.)

Once set, internal re-inforcement, pipes, conduit etc cannot be inspected or corrected.

It doesn't like some environments and "decays" in some instances.

And as was said before "It's heavy" (Meaning that all other portions of the engineering process have to accomodate the forces involved.)

It often cracks (Even when correctly designed and poured) which can allow moisture or contaminants through.

It's not homogeneous. (This leads to all sorts of problems relating to thermal expansion, attaching things to it and so on.)

(And this is from an EE, wait till the Mechanical and structural guys get into it.)

Hello JustanEng,

Comments to your "Demerits of concrete as an engineering material!"

Consider concrete in tension. (It's no good!)

It is very good when reinforced with steel reinforcement.

Consider it's failure symptoms. (Sudden and catastrophic failure)

Properly reinforced concrete does not result in sudden or catastrophic failure.

Consider the manufacture of the raw cement. (Energy hungry process)

I don't know anything about that, perhaps you are right.

Cement dust is hazardous. (So drilling/cutting etc require protective equipment.)

Okay, that is true.

Once it's set it cannot be re-shaped. (See separate threads about the refrigeration plant with a leaking pipe somewhere under concrete slab, garage floors with sinking slabs, houses with water oozing up through the carpet and the list goes on...)

O.K.

Once set, internal re-reinforcement, pipes, conduit etc cannot be inspected or corrected.

Agreed!

It often cracks (Even when correctly designed and poured) which can allow moisture or contaminants through.

Agreed.

It's not homogeneous. (This leads to all sorts of problems relating to thermal expansion, attaching things to it and so on.)

You are absolutely right. It is not homogeneous. And it is not isotropic. It may lead to some problems, but they are easily rectified by taking normal engineering design precautions. The material is not perfect by any stretch of the imagination, but it is still the best we have!

I was feeling all lethargic about this post till an EE put pen to paper. Then, shaken by the lack of knowledge that EE demonstrated, thought about firing off a rocket. Saw the excellent measured response from BA/AEL (in french BA is Béton Armé which is reinforced concrete, can this be a coincidence, and even BA(a)EL is Béton Armé aux États Limites, surely more than a coincidence) and thought what a better response might be.

Some additional comments to those already posted (mine in italics):

Consider concrete in tension. (It's no good!)

It is very good when reinforced with steel reinforcement. Or Glass fibres or steel double headed nails or when using one of the new concretes being developed along with ceramics which allow tension.

Consider it's failure symptoms. (Sudden and catastrophic failure)

Properly reinforced concrete does not result in sudden or catastrophic failure. Generally there is a plastic phase of distortion (reinforcement extends allowing concrete to crack thereby giving signs of failure prior to full failure) which is also associated with a plastic analysis of the framing system (if a member fails then it will generally hinge at the failure point and redistribute the load through the system).

Consider the manufacture of the raw cement. (Energy hungry process)

I don't know anything about that, perhaps you are right. Everything is energy hungry but we can work to reduce this. Including transport.

Cement dust is hazardous. (So drilling/cutting etc require protective equipment.)

Okay, that is true. Even drilling and welding are hazardous. Normal precautions need to be taken.

Once it's set it cannot be re-shaped. (See separate threads about the refrigeration plant with a leaking pipe somewhere under concrete slab, garage floors with sinking slabs, houses with water oozing up through the carpet and the list goes on...)

O.K. Once a building is in place it is expensive to do extensive repairs. Designing it properly in the first place, taking into account the building process, is how it is supposed to happen.

Once set, internal re-reinforcement, pipes, conduit etc cannot be inspected or corrected.

Agreed! Properly designed and installed pipes should not need inspection. Again, this is where the design process has had shortcuts occur due to time, money or inexperience.

It often cracks (Even when correctly designed and poured) which can allow moisture or contaminants through.

Agreed. Not agreed. The crackwidth can be determined based on the level of reinforcement. It can be designed to 0.1mm crackwidth which is achievable and done for underground archive areas. Caltite or other products are available with repair kits and lifetime guarantees. Normal competent contractors can pour with very few errors. Do not cut corners - all will be well. I have worked on some of the best concrete finishes and it is quality control and good design of the pouring process which are essential.

It's not homogeneous. (This leads to all sorts of problems relating to thermal expansion, attaching things to it and so on.)

You are absolutely right. It is not homogeneous. And it is not isotropic. It may lead to some problems, but they are easily rectified by taking normal engineering design precautions. The material is not perfect by any stretch of the imagination, but it is still the best we have! There are very few homogenous engineering materials: timber, GRP, rolled steel, extruded metals, plastics. Concrete is only one. The rate of thermal expansion of steel and concrete is relatively the same (about 8 to 12 x 10^-6 microstrains/°C compared with steel 11 x 10^-6) and few real problems are encountered when correct design is done.

I actually went to a 'concrete museum' (Ok I know I'm sad) which showed the development of various reinforced and pre stressed concretes.

Some one had actually made a working bow (as in bow and arrow) out of concrete just to prove how versatile prestressesd concrete is
They also made a concrete canoe
...pretty mad but cool in an engineering way.

Del

Where is this Concrete Museum, I'd love to see it some day!

I think it was at or near the Weal and Downland Museum... maybe it was a temporary exhibition.

Just did a search for 'concrete museum' which came up with here which maybe right as I know it was somewhere in that region of the South Downs.

I see you are in the USA, so it's a bit out of your way!

Del

Ouch!!!

Guys/gals if you think that I don't know of the merits of RE-INFORCED concrete (As distinct from concrete alone.) then it's a sorry world.

The fact that concrete needs re-inforcement to become so widely used is evidence that concrete (As the original question asks) as an engineering material has significant de-merits.

Those de-merits can be overcome (and obviously are) by the judicious use of design and testing that have been developed over the centuries of its use within a system that utilises the merits (like good performance in compression) combined with the merits of other materials (Especially regarding tension conditions.).

The originator then asks specifically to focus on the demerits. I simply answered with facts relevant to concrete. (Not re-inforced concrete, not pre-stressed concrete, not lightweight concrete, not any other modification.)

If the question had been about the merits/demerits of concrete building systems then my answer would have been substantially different.

Hopefully this response does not sound "self defensive", but rather focusing back to the original question and request as posted.