Environmental and health benefits of lime

Environmental and health benefits of lime.

Reduces carbon dioxide (CO2) emissions

  • Increasing levels of CO2 in the atmosphere is the main cause of climate change. Below is an explanation of why lime produces lower CO2 emissions than cement.
  • Like cement, lime gives off CO2 during manufacture, but re-absorbs it when setting. Because of this we can say that the use of lime in construction is close to carbon neutral (in the same way that biofuels are – because plants absorb the CO2 given off when the fuel is burnt). This is of course not absolutely correct, as CO2 is given off not only from the lime, but also from the fuels used to burn it and transport it. But it’s much closer to carbon neutral than cement.
  • Cement itself actually releases less CO2 on burning than lime, but as it is burnt at higher temperatures, it takes the lead again when the fuel used is taken into consideration. It also re-absorbs some CO2, but very little compared with lime
  • Burning CaCO3 produces CaO + CO2
  • Slaking: CaO + H2O produces Ca(OH)2
  • Carbonation (setting): Ca(OH)2 + CO2 produces CaCO3 + H2O
  • Any given weight of lime will absorb around its own weight of CO2 from the atmosphere; here we are talking about non-hydraulic lime of course. The more hydraulic the lime, the less carbonation takes place; with extremely eminently hydraulic lime there is almost no carbonation required for the lime to set.

Reduction of emissions of pollutants

  • Lime is burnt at 900°C compared to 1200°C for cement. This means fuel savings and lower pollution levels.
  • even without considering the fact that lime absorbs atmospheric CO2 to set, emissions in the actual manufacture of lime are 20% less than for cement. The cement industry is responsible for around 15% of global CO2 emissions (which will increase dramatically as countries like China and India develop and begin to encase themselves in concrete like we have), and around 6% of CO2 emssions in the UK.
  • Lime is less dense than cement – saves on fuel for distribution (and therefore reduces emissions of pollutants).
  • Unlike lime, cement production releases heavy metals into the atmosphere.

Local, small-scale production

  • Limestone deposits are widespread.
  • Best fuel for kilns is wood – also a widespread, natural resource (wood burns at lower temperatures, and slowly; faster, higher temps could close pores in quicklime, making it less reactive when it comes to later stages in the lime cycle – slaking and carbonation).
  • Lime kilns used to be found in most villages. now cement production is centralised in large factories with national and international distribution networks. This has occurred not just because of the speed at which structures can be thrown up using cement, but also because of the economies of scale that this type of production brings. But because those small lime kilns don’t exist now, it’s going to be difficult to re-invigorate the lime industry in the places it used to be, and where limestones can be found. Can you imagine the planning difficulties of opening new lime quarries / kilns in the Chilterns or Cumbria? And the locals may not be too enthusiastic either. It’s the same with wind turbines. People understand the need to cut CO2 emissions, but don’t want anything that helps on their doorstep. We have to challenge ‘nimbyism’ and encourage small-scale, local industries and energy generation if we really want to fight climate change, whether they are on our own doorsteps or not.
  • Local production can reduce transport distances.
  • Lime is very compatible with other local, natural, breathable materials such as earth, straw and stone, as they tend to be porous, so that lime adheres to them well and helps retain their natural breathability and flexibility; and so the use of lime allows a range of other natural materials to be used too, so that in theory, for a new build, you could source only environmentally-friendly, biodegradable materials for your home. Cement is incompatible with natural, breathable materials and so using cement removes this option.

Recycling

  • Lime mortar can be removed from bricks when buildings are demolished and the bricks can be re-used. Bricks with cement mortar are only good for hard core.
  • Around 3 billion bricks are fired annually in the UK; think of the fossil fuel use and associated CO2 and pollution emissions that causes. These bricks could last for centuries, but because of the nature of modern buildings (eg supermarkets) they last only for decades, and then end up as hard core.

Health benefits

  • Cement can have up to 5% silica content, in the form of silicon dioxide, which can cause lung scarring (silicosis).
  • Chromate (a trace impurity in all cements) can cause dermatitis and stomach cancer.
  • Cement additives such as industrial slag and pulverised fuel ash can be radioactive.
  • (Limewash): WHO report – decorators using conventional paints are 40% more likely than average to get lung cancer, and 20% more likely to get other cancers, due to VOCs from solvent-based paints.
  • Modern houses are hermetically sealed with non-breathing materials like cement, impervious paints and plastics, instead of breathable materials like lime, wood, earth, natural paints etc. Consequently, one in six children now have asthma, yet it was virtually unheard of 60 years ago. (Increases in traffic, and chemicals in cleaners, furniture, building materials and plastics have also played a part).
  • Portland cement contains hexivalent chromium, and there is a warning on the bag that this ‘can cause allergic reactions’. This is a bit of an understatement, as it’s carcinogenic, which is bad news for people who are constantly working with it, or sweep up cement dust.
  • Sick building syndrome (which means of course that you get sick not the building) – associated with fumes from petrochemical-based paints and other synthetic materials, especially if combined with poor ventilation.
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