Cement And Global Warming
Recent news in papers gave out Agricultural Minister's statement that since farming is not economical; the farmers should do some other work also. "We have adequate foreign exchange and if required, we would import food from outside for our people" was his additional remark in it. Next day, foreign news was that due to environmental pollution, crop in USA is reducing by about $500 Million t every year for the last few years. (the cost of Indian import will be high therefore.) For the last few years, we are seeing that cities like Mumbai, Pune, Patna, Kolkata etc are getting heavy rains in monsoon and therefore lot of people suffer in the Nature's fury.
Cities or towns are concentrations of population. They thus create pockets of large heat islands in the districts. This extra heat provides fuel to the storms that may be passing through especially during monsoon/summer. Since tall building jut up into the atmosphere over the towns/cities, they cause wind drag. This creates a sort of boiling action of upward-moving air than increasing rainfall. Vehicles and industry (in cities) emit tiny particles (aerosols) suspended in the air. They tend to move at higher level over towns/cities. Though aerosols have been thought to suppress rainfall, researchers at Princeton University have found that they may increase rainfall during storms. They have observed that during the extreme thunderstorm that hit Baltimore in 2004, about 30% more rainfall fell in cities/towns as compared to countryside.
The Sun provides heat and light to its planets. Earth is populated and since UV portion of the rays are harmful to the skin and eyes of the life on earth, the sunrays could play havoc with the life there. The Nature has therefore provided a barrier at the top of the stratosphere in the form of Ozone layer. This layer is created by the reaction of UV rays on the oxygen molecules in the atmosphere. The reaction creates Ozone and it offers a filter to the sunrays. The layer only permits the sunrays without UV portion through it and thereby likely damage to the life on the Earth is prevented. Therefore, this is known as 'Good Ozone Layer'. This layer is within 35 to 50 Kms above the sea level. Man has started industries for his requirements around 200 years ago. The Chlorofluorocarbons (CFC for short) in the Industrial effluents rise in the atmosphere, reach the stratosphere edge where it meets the 'Good Ozone Layer'. The Halide atoms in the chemical react with the Ozone molecules and break them into oxygen atoms and molecules. Ten Halide molecules can destroy or break up to one million Ozone molecules before becoming ineffective. This tears the Ozone layer and creates holes in it. These holes permit the harmful UV portion of the Sun rays to reach ground level. About 10% of ozone (in the atmosphere) is located below 35 km above the sea level. At its own slow natural rate UV portion does repair/patch up the Ozone layer holes at the top. 30 Million Sq Km hole observed in 2000 was measured to be 15 Million Sq Km in 2002 on the North Pole. The CFCs are mainly used in refrigerators, cold storages as solvents and in chemical sprays (aerosols). New technologies are needed in these cases to prevent destruction of the protective Ozone layer at the top of stratosphere. Replacing these chemicals with Hydrochlorofluorocarbons (HCFC) has been suggested as immediate temporary measure, since the life of halide atoms in HCFC molecules is very short in the atmosphere as compared with that of CFC currently in use.
The breathing-outs by the living entities in localities give out Carbon-Dioxide to the environment and pollute the same. In a year, a person emits about 170 kgs of Carbon-Dioxide pollution in the atmosphere by his breathing. This emitted Carbon-Dioxide can be consumed by the trees as it is required by them during the sunlight to growing. In presence of sunlight, the plant converts Carbon-Dioxide and water into glucose which is their food. It has been noticed that one Hectare of rain forest (with trees at about 3 Meters intervals) can consume about 340 tons of Carbon-Dioxide per year (and atmosphere gets rid of Carbon-Dioxide to that extent). This is the primary reason why forest must cover at least 33% of the surface area of any country. Currently due to heavy deforestation, this is reduced to even below 22% in most countries and population is rising to increase the pollutant gas in the atmosphere.
The exhaust of oil driven vehicles contain lot of Nitrogen oxides (NO2), Sulphur Dioxide (SO2) in addition to Carbon-Dioxide (CO2) and other gases whereas industrial effluents contain many Volatile Organic Compounds (or VOC for short). Both of these emissions together in presence of sunlight react with the oxygen in their track and a smog containing ozone is created at the surface level. This smog can move anywhere due to wind action. Presence of this smog prevents the plants from using Carbon-Dioxide from the atmosphere restricting their growth appreciably. Fresh concrete is understood to be absorbing some quantity of Carbon-Dioxide from atmosphere at the setting. This, in addition to maintaining Carbon-Dioxide pollution in the atmosphere, prevents its consumption by the plant life and retards its growth. The reduction of food production in USA in the last few years appears to be the result of this pollution. United Nations has warned India about the likelihood of reduction of 18% crop production, in current year due to the same reason.
Because of the holes in the Good Layer at the top, certain UV rays do penetrate and reach the earth surface. They react with the oxygen at that level and create Ozone layer. This, with the smog creates breathing difficulties to the life in addition to retarding plant growth. Therefore, this is known as Bad Ozone Layer'.
When Carbon-Dioxide pollution spreads in the atmosphere, it becomes a layer at appreciably low height above the surface. When the sunrays reach earth surface and heat it up, the rays are expected to reflect in the stratosphere with their reduced load of heat. But due to the Carbon-Dioxide layer, the reflected sunrays get trapped in lower atmosphere only and Green-House effect is created. Earth does not get cooled in the evenings and average temperature of earth rises. This is the well-known phenomenon of Global Warming. Seasons change drastically creating difficulty for respiratory system of living entities. The polar ice caps melt. Icebergs start moving to the equator. The ocean level rises; quite a large acreage of coastal land gets under sea. Some islands in Pacific Ocean have already been sunk and Mauritius is in danger of going under. The polar bears, unable to find thick icy ground, are dying in large numbers. According to UNO, 40% of species are likely to be extinct soon unless Carbon-Dioxide and other polluting gases (together known as Green-House-Gases) are removed from the atmosphere quickly. In mid-2005 GHG has been estimated to be to the tune of 200 Gigatons!
In view of above, it has become urgent that along with reduction of vehicular and industrial effluents, Carbon-Dioxide in the atmosphere must be reduced for safety of life on our earth. Cement concrete construction is found to be one of the important constituents of the polluting processes in this regard. While manufacturing cement (even by dry process) one ton of coal/carbon is required to be burnt for producing 10 tons of cement in rotary kiln. (Wet process needs 3.5 tons of coal/carbon to be burnt for manufacturing 10 tons of cement). Three tons of coal/carbon burnt release seven tons of Carbon-Dioxide gas in the atmosphere.
During the year 2006 as per information, India has used 200 million tons of cement for construction of new as well as repairs of existing structures. Thus on the average 17 million tons of cement has been consumed per month. Cement gives out during its complete hydration around 140 calories of heat per gm. Out of this 90 calories are released in atmosphere (during hydration and gaining designed strength) in first month itself. Thus 3 calories are given out per gm of cement used every day. During 2006, in this way cement has released in the atmosphere (in India) on the average of 51 Trillion Calories of heat; daily. Cement used in previous months would have been giving out heat at a lesser rate in addition. This is the direct contribution to the Global Warming by cement consumption.
Assuming all the cement manufactured during 2006 was by dry process alone, 20 million tons of coal was consumed. This coal would have generated 73.3 million tons of Carbon-Dioxide gas to pollute the atmosphere. As per CGD Washington report, India is annually emitting about 638 Million Tons of Carbon Dioxide (as the third largest emitter in the world). Thus Cement manufacturing contributes more than 11% of the emission. It needs prompt tackling.
Most towns/cities contain concrete structures which absorb heat during the day and reflect it back to the atmosphere during the cooler nights. This makes the towns/cities 4 to 8 degrees Fahrenheit hotter than the surrounding lands. This ensures that stronger winds and heavier rains come to the cities as compared to the surrounding land.
Rate of consumption of cement is considered to be a parameter to measure the developmental stage of a country. India is only a developing country and hence other (developed) countries must be producing and using lot more quantity of cement. How much Carbon-Dioxide gas for green-house effect and heat for Global Warming they must be adding will surely be a mind boggling figure. Civil engineers being aware about environmental pollution better, it is their responsibility to control the pollution because of own activities.
Therefore cement, as a premier material for development, needs to be drastically reduced from manufacturing and use in whole of the world to control pollution by Green-House gas effect and Global Warming. Don't we agree to replace cement with some other better (less polluting) building material soonest?
Why not consider reviving the 'freshly ground slaked lime masonry' system abandoned during early 20th century in India? Construction of bridges on Gangacanals near Roorkee constructed in lime masonry long back are still in usable condition (without undue maintenance) is a good guiding example for our engineers to follow. This technology is still available with us and as a protector of Nature by tradition, Bhaarateey engineers must come forward and make the authorities discourage use of cement with immediate effect in our projects and encourage freshly ground lime masonry in lieu, to save lives on Earth. To reduce the use of cement with immediate effect, we may undertake use of porous concrete, replacement of appreciable quantity of cement (in concrete) by materials like fly ash, Ground Granulated Blast Furnace Slag (GGBFS) or some other pozzolanic material.
It is known that lime masonry cannot be used for constructing structures more than 3-4 stories high. But then we should restrict our construction within this height to avoid use of cement. Moreover, tall structures are found to be susceptible to more severe damage in earthquakes and whole world is currently considered to be falling under one of the five seismic zones of varying severities. As Bhaarateey people, we are accustomed by tradition; to align all our activities in line with nature at all times to get its continued protection to the life on earth. In case other countries like US are not ready to follow suit immediately, let them. We must urgently start to follow this track ourselves. Since we are inherently JAGADGURU, it is our responsibility to guide the world to follow Right Path by our example. We must import our (other industrial products) requirements from other countries which will be polluting the nature the least. This will persuade others to follow the path. Since our path is friendly to Nature and therefore in the interest of lives on earth, nay, the earth as a living planet, it is essential that all follow this path with immediate effect.
- Literature on "Global Warming" being published on internet since last few years
- "Concrete Technology" text book on concrete by Prof M S Shetty
- "Cements and Concrete Mixtures for Sustainability" by Mehta, P. Kumar published in Oct-Dec 2007 issue of ACCE (I) Bulletin.