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Products: Is it acceptable to use Ordinary Portland Cement [OPC]?

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    • CommentAuthorMike George
    • CommentTimeApr 10th 2008 edited
     
    I've asked Keith if we can have a poll on this but in the meantime I would be interested to read views on this.

    No sitting on the fence please, Answers are:

    Always
    Sometimes
    Never
  2.  
    Sometimes - if you need pre-stressed spans. Otherwise no, in my book.
  3.  
    Sometimes. I doubt we could manage without it entirely in an industrial society. Surely the energy consumption in manufacturing cement should be seen in the context of the usefulness of the product. without OPC, I should imagine our infrastructure would be in ruins within a decade.

    I'd like to see more use of less energy hungry alternatives where possible. For example, compressed earth blocks or hemp lime blocks instead of concrete blocks in buildings, and less energy intensive types of cement. Failing that, more sparing use of OPC, for example in foundations which often seem over the top to me.
  4.  
    Just poured 18m2 into a footing
    so I guess always
    I'd love a alternative to be in common use , but I feel at the mercy of designers,engineers and building controls
    Anybody know much about mirco piles as a OPC free footing ,
    Until I can find customer happy to pay for the preferred alternatives , theres no choice
    • CommentAuthorjon
    • CommentTimeApr 10th 2008
     
    Often the least expensive solution to a set of design requirements is also the lowest annualised carbon cost. So sometimes it is acceptable and is occasionally preferable carbon-wise to all other solutions.

    OPC is a high energy product with some high value characteristics. If we need high value characteristic materials for a building but do not wish to use OPC (or steel, aluminium or other high energy products) the solution may be to change the design requirements rather than to look for ways not to use the materials that are best suited to that design.

    Micro piles are usually OPC James unless Mirco is a tradename or you mean the small screw steel type.
  6.  
    Building regs allow a concrete strip foundation rather than trench fill. Then start building straight out of the ground. I used some spare sawn up concrete paving slabs in an extension done last year. Cuts the volume of concrete down. My old house didn't have any foundations worth speaking of. I think they just chucked some big slabs of stone in a hole and started laying the bricks.
  7.  
    Jon
    I ment the small screw steel ones you mentioned, i know nothing about them, but they seem a good alternative to
    trench fill/traditional footings
    Strip foundations a good idea, to reduce trench fill , but on deeper work it a bit tricky
    the footing mentioned above was 1.8m deep , 800 deep trench fill , block up to dpc
    and the brickies still moaning that I didnt fill it higher

    cheers Jim
    • CommentAuthorjon
    • CommentTimeApr 10th 2008
     
    They can be used in some types of soil. However, bear in mind that a steel screw in micropile will have a higher embodied carbon content than an OPC micropile

    Also bear in mind that the NHBC guidelines are quite specific about the uses and minimum depths: The regs are safety driven whereas the NHBC is more insurance driven meaning strips can sometimes only be used in cases where no insurance is required.

    A low embodied alternative for low level housing units, if you can be bothered, is to dig in small segments down to good bearing strata, use the maximum stress allowable at that level. bring up the (lightly OPC'd) hole up to ground level and then use PC units as your 'foundations' off which to spring everything else: Works out at about 1/3 the CO2 content typically (I have used it as an option in some level 5 proposals).

    jon
    • CommentAuthorchipedwood
    • CommentTimeApr 10th 2008
     
    Just reasoning my vote:

    I say it is always acceptable to use it.

    It's a very good material but I do think that it should be used more carefully than it is.

    Like in this flat, a concrete floor was put in upstairs replacing a wooden one when it became rotten. That I consider stupid and should't have been done.
    • CommentAuthorbiffvernon
    • CommentTimeApr 10th 2008
     
    Always use it for airport runways, multistory carparks, motorway bridges, nuclear power stations, er, hang on, we won't need any of those things.
    • CommentAuthorTheDoctor
    • CommentTimeApr 11th 2008
     
    With the current population density, it is an essential material.

    Effective public transport RELIES on population density.

    Density RELIES on an element of high rise to maintain green spaces in the population centres

    there are also huge economies of scale in materials, energy consumption etc in population density.

    spreading everyone out to their hypothetical 1 acre per person of the UK land mass would be a disaster

    OPC is a part of that density solution, although its use could be limited and more carefully considered
    • CommentAuthortipper
    • CommentTimeMay 10th 2008
     
    OPC is essential but an alternative material that has the same strength and flexability would be good. I heard that for every ton of concrete made a ton of co2 is produced. Tell me if i am wrong!
  13.  
    I have heard that statistic too. It would be interesting to have a comparable figure for lime don't you think?
  14.  
    Sometimes, especially for wind turbine bases.
    • CommentAuthorbiffvernon
    • CommentTimeMay 12th 2008 edited
     
    Wind turbine bases and tidal barage works.

    (That is such a small proportion of current usage it appoximates to 'never' for the purposes of my vote at the top of this thread.)
    • CommentAuthorDr T
    • CommentTimeMay 25th 2008
     
    The use of OPC is an acceptable medium but only when alternatives are not suitable. One should always weigh the production carbon footprint against the life-span of the poduct.
  17.  
    Yes, but what is the carbon footprint? OPC reabsorbs CO2 from when it commences setting, as does lime, and I don't think this is included in any calculations,at least not in any I've seen. It is heated to a higher temperature than lime, so uses more fuel to make (Biff pulled me up about this on another thread,when I asserted that the carbon footprint for lime and opc were about the same, and he was right) but apparently it can be fired at a lower temperature than it usually is. So I don''t know what that's about.
    for myself, I do use it sometimes, in small quantities.
    • CommentAuthorbiffvernon
    • CommentTimeMay 25th 2008 edited
     
    Posted By: paul.dixon27 OPC reabsorbs CO2 from when it commences setting, as does lime,
    No, very little of the CO2 is reabsorbed by OPC as it sets, while all of the CO2 is reabsorbed when lime sets. The reaction calcium carbonate to calcium oxide to calcium hydroxide to calcium carbonate is known as the 'lime cycle' and has no net production of CO2 once the cycle is complete (other than from the fuel used, of course, which as we have seen is less in lime making than OPC making). When cement sets there is very little reabsorption of CO2 from the atmosphere as it is the silicates from the baked clays that do most of the action.
  19.  
    Biff, would you hazard a guess as to the amount of CO2 produced in the energy per tonne of lime? I am still intersted in how much less energy is used than OPC
  20.  
    OPC has a chemical set but doesn't stop absorbing CO2 when it solidifies. Being less porous, It takes longer than lime to absorb it but the same 'lime cycle' is going on.
    • CommentAuthorbiffvernon
    • CommentTimeMay 26th 2008
     
    Yes some CO2 continues to be absorbed but not much - order of magnitude different to lime. Most of the calcium forms silicates not carbonates.
    • CommentAuthorRachel
    • CommentTimeMay 26th 2008
     
    Nope... by the way, regarding footings, recent tests carried out by amazonails for a planning dept showed that rammed earth tyres are actually stronger than concrete! A tad more laborious, but think of co2 savings...
    Re concrete CAT records show that 40% or the worlds energy goes on making concrete and I heard it is around 7% with lime, altho lime is continously carbonating over years and years.. go go lime...
  23.  
    Thanks Rachel, thats very interesting, considering the amount of concrete used relative to lime. Perhaps the energy used in production per unit/mass is closer than many suspect?

    Don't get me wrong, I have nothing against lime. But I would like to know just how green it is in production . If concrete is such a bad boy I would like to know just how bad
    • CommentAuthorbiffvernon
    • CommentTimeMay 26th 2008
     
    Mike, I had a tour round Singleton Birch's limeworks a little while ago. If you can't find the data you want on their website: http://www.singletonbirch.co.uk/ get in touch with them. They have a very helpful techie department.
  25.  
    Posted By: RachelRe concrete CAT records show that 40% or the worlds energy goes on making concrete


    Nonesense.

    From http://www.buildinggreen.com/auth/article.cfm?fileName=020201b.xml

    "In the United States, producing the roughly 80 million tons of cement used in 1992 required about .5 quadrillion Btus or quads (1 quad = 10 15 Btus). This is roughly .6% of total U.S. energy use"

    You're off by almost two orders of magnitude. Perhaps you're thinking CO2 emissions? 36% of total CO2 emission come from industrial processes of which cement is a large contributor - but it comes out closer to 10% of the world total. So you're still off by a factor of four.

    Paul in Montreal.
    • CommentAuthorMike George
    • CommentTimeMay 26th 2008 edited
     
    Posted By: biffvernonMike, I had a tour round Singleton Birch's limeworks a little while ago. If you can't find the data you want on their website:http://www.singletonbirch.co.uk/" rel="nofollow" >http://www.singletonbirch.co.uk/get in touch with them. They have a very helpful techie department.


    I was hoping that those who say OPC should never be used would be able to come up with some figures which justify their stance - perhaps the figures do not make happy reading? Are you in denial? :bigsmile:
  27.  
    Looking at the singleton birch site, I cannot find figures for how much energy is used in production. Apparently, they are the UK's biggest producer of lime, which got me thinking more. What proportions of Cement/Lime are sourced locally? and what would be the implications of a major increase in lime use? Does most come from abroad? Would it need to?
    •  
      CommentAuthorted
    • CommentTimeMay 26th 2008
     
    •  
      CommentAuthorted
    • CommentTimeMay 26th 2008
     
    Oh, and if you're really short of reading matter for this Bank Holiday then there is this lot as well:

    http://www.wbcsdcement.org/research.asp

    If you are short of free time then Reports 6 and 8 are the main ones.
    • CommentAuthorMike George
    • CommentTimeMay 26th 2008 edited
     
    Thanks Ted, the BFF article indicates lime as producing around half the CO2 emissions of cement. But also says

    'some hydraulic limes are capable of reabsorbing nearly all of the CO2 released in their formulation, but this figure does not account for the C02 released in the kiln which can be on a par with cement'

    Not really clear that!

    It makes no comment of energy used in transportation.

    The other reports do not appear to draw comparisons with lime, though I have only scanned the two you note.

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