In late fifties when we civil engineering students of Government College of Engineering Pune were taught this subject of cement concrete, it was emphasized that Concrete structures like bridges will last for over 60 years whereas residential accommodation can give satisfactory service for over 100 years! The cement concrete was quite strong and durable, even better than “finely and freshly ground lime” under use then. Even RCC was started being used by engineers with success.

 

We students were awestricken with the new found material and the technique of its use. The mix design for 1:2:4 (volume batch concrete) RCC, we used to need 15-16 one CWT (112 Lbs) bags of cement to make 100 cft of finished concrete. Sometime the cement consumption could go up to even 17 bags.

 

The mix design was introduced with a hollow box (3’ x 3’ x 3’) packed fully with coarse aggregate additionally packed with fine aggregate and in turn this interfiled with finer powder of cement. The body of concrete being aggregate the cement was only the binding agent as we could understand. 

 

Any more small voids in this box were supposed to be filled with the expanding cement gel after it reacts with the mixing water in the concrete. The resulting concrete was supposed to be even waterproof. 

 

We the engineering students were really overwhelmed by the good qualities of the cement and began enthusiastically looking forward to design cement concrete structures. By that time British and other foreigners had progressed into pre-stressed and/ or post-tensioned concretes. Indians accepted that as well as a technical gift from West. Concrete designing had become a science and wordy wars about volume batching versus weigh batching were fought in technical journals with gusto. Whatever concrete construction was executed before Second World War in India was by the British Engineers done through the Indian ‘Mestries’. They had no restriction of time or money for the projects and accordingly these constructions are standing even today as good examples. (Of course, now the British or other Western engineers have relaxed their vigil and got confused due to the large varieties of cements in the market, their output is dropped to ‘average’). Indian engineers used concrete since independence without teaching their masons and mestries the correct techniques needed to use this new material properly (since they themselves were unaware of that aspect). Cement was being used as readymade ground lime only. The engineers took it to increase the strength or durability of concrete, one needs to add cement in excess to the mixture. 

 

Once a boxed structural member was concreted, the sample of the concrete used therein was to be cast in cubes and after proper curing; the cube was to be crushed to determine the quality (compressive strength) of the concrete used in the member. Bureau of Indian Standards brought a standard for this cube test and use of concrete to give impetus to good concrete construction. After they published IS: 456 of 1978 regarding use of plain & reinforced cement concrete giving the direction to use more cement (up to 540 Kgs per CM3 of concrete) for durability consideration, use of more cement for strength as well as durability purposes became rule rather than exception. Most of the ‘experts’ included in the BIS committee on Cement Concrete Section are either representing large construction companies or cement manufacturing companies who were only interested in increasing the use of cement to earn more money. They were not necessarily interested in propagating use of some other material in construction. Isn’t it? Not only cities but even small towns became concrete jungles and no wonder the mother Earth reacted by increasing environmental temperatures everywhere. 

 

Cement factories grew in number as well as size and they manufactured special cements not only for refractory or sulphate resistance purposes but also to give higher strength in compression (instead of 33 N/mm2) of 43, 53 or even higher (at the end of 28 days curing). When the manufacturers professed that the stronger concrete is more economical, gullible people, even engineers, enthusiastically started using it in their designs. This was the time when dangers of cement concrete even with reinforcement were started appearing on horizon. Defects like, rusting of steel and carbonation of concrete, cracking of “stronger” cement concretes after a few days use, deterioration of the concrete members after a few seasons of intensive (though within designed loads) use, destruction of concrete because of alkali-aggregate reaction in certain circumstances, cracking of concrete with excessive cement quantity leading to destruction of the monolith, members failing because of inadequate concrete strength development etc. made frequent appearances. Deterioration of Vashi Bridge near Mumbai and failure of many bridges like Mandovi River Bridge in Goa as well as overhead tanks, multistoried concrete residential buildings etc compelled Indian civil engineers to wake up and study the technology and its application in India thoroughly. According to their thinking, the defects might be due to various reasons like the pour was incorrect, segregation might have taken place while pouring, placement of reinforcement might not be exactly as per design or might have been shifted to wrong places during concreting or the compaction might not have been done effectively or the curing might not have been done correctly or defect might be in erection and/or removal of form work. Moreover, even when the test cubes were cast along with the member being concreted, further progress in concreting was never held up (as obstacle to maintain progress of work) till the 28 days crushing strength of the cubes certifying the strength of the concrete became available to the site engineer. In the name of progress, the constructors gave more importance to the test cubes being cast and tested successfully than the concreting of the members themselves (to avoid any future problem arising in case the test results were not found satisfactory). This led to having individuals other than site engineers specializing in casting of test cubes. This was found to result in the cubes not really as representative a sample of the concreting of the member as desired. In addition to the use of excessive cement in concrete, this and other shortcomings in use of correct technology and procedures led to the defects in concrete that have surfaced in India over the years. 

 

From the basic principals of concrete technology one can list following essentials of strong and durable concrete by using Ordinary Portland Cement:-

 

1. Cement is only binding agent and has hardly any inherent strength as a material. It can adhere to surfaces of strong pieces as gum and give strength to the monolith body.

 

2. For convenience, pieces of stones as aggregates of various sizes are considered suitable to give a body to concrete. To have cost within limits, quantity of cement should be small and sizes of coarse aggregate pieces be as large as possible in the mixture.

 

3. The cement only binds the various aggregate pieces together to make the concrete monolith. Since cement as binder has no inherent strength, the binding layer should be as thin as possible. Moreover, cement being in very fine form has a high coefficient of thermal expansion/contraction compared to that of aggregates used and hence thinner the layer, safer it is. So cement must be used as least as practicable.

 

4. Strength of concrete has very little bearing on the quantity of cement in the concrete in the long run. Larger the (than necessary) quantity of cement, the concrete is likely to deteriorate over time faster due to temperature variations in the environment.

 

5. To make concrete stronger, less voids or gaps should be permitted in the concrete monolith. This is possible by using all the intermediate sizes of aggregate (to reduce the size of gaps) and adequate compaction of the concrete in-situ after pouring. Water should be just sufficient to make the rich chemical gel with cement. Extra water remaining if any is likely to create voids after evaporation.

 

6. In the concrete mixture only cement is a manufactured substance and hence is more susceptible to environmental damage and deterioration and hence least durable.

 

Therefore, thinnest possible gel around the aggregate pieces is all that is needed to make a durable concrete.

 

7. In short, to make strong and durable concrete what we need is well graded aggregate to fill the volume of concreting (box?), added with minimum required cement to cover the interstices with strong gel formed with little more than essential, say within 40% water as compared with cement quantity. To make it durable, prevent any voids within the monolith by adequate compaction. You can provide compaction such that the strength of the concrete is as designed.

 

The mixture must be uniform and before setting time of the cement is reached, compaction must be completed. Once concrete is cast and set, it should be cured with water at least for 7 days and then damp curing may be satisfactory.

 

8. If possible and convenient, it is suggested that concreting can be done by first filling coarse aggregate in the centering boxes and colloidal mass of sand and (water added) cement is poured to fill the voids before compaction. This will ensure that the semi-elastic gel that is produced by the colloidal mixture will be able to coat the aggregate pieces effectively with less cement at the same time giving better strength.

 

9. As far as reinforcement is concerned, the quantity of steel as designed must be placed at correct locations to resist tensile stress development in concrete. It must be ensured that the steel reinforcement bars do not shift during pouring and compaction of concrete. Adequate concrete cover must be around the reinforcement to prevent environmental carbon-di-oxide, chlorine or moisture from reaching the bars and corroding them.

 

In short, it can be seen that once the ingredients of concrete are properly selected, ensuring W/C ratio around 0.4 and adequate compaction to prevent any voids in hydrating (cement in) concrete are the only ways to ensure strong and durable concrete. If these conditions are adhered to, then adding any extra quantity of cement (per cubic meter of concrete) has no positive effect on the strength or durability of concrete. Rather more cement is likely to make the concrete less durable since thicker cement layer will have more shrinkage/ expansion than other ingredients of concrete as environmental temperature wane and wax giving rise to destruction of the monolith.

The cement is required only to surround the aggregate pieces for binding neighboring pieces. The maximum size of aggregate (MSA) will determine the quantity of cement required per CM of concrete. As the MSA decreases, the required cement quantity will increase since the surface area of the smaller aggregate pieces (to be bound together) will increase. Normally, for RCC we use 20 mm MSA. When this size increases (like for road or foundation purposes) to, say 40 mm, then naturally cement quantity will reduce by around 10%. For soil stabilization, cement is mixed in soil (comparatively coarser, even sandy) at not more than 10% by volume. As soil becomes clayey and finer, the cement content may go even up to 25%. This is natural, since surface area of particles to be covered by cement increases appreciably. The unrestrained compressive strength of this stabilized soil becomes about 6 Kgs per mm2. If properly restrained and compacted the resulting compressive strength, it can be comparable with concrete. Thus compressive strength will depend on compaction and W/C ratio only. For a cubic meter of concrete (MSA 20 mm) about 1300 litres of aggregates are required. Accordingly, for cementing purposes, 160 Kgs of cement should be sufficient. Some small additional quantity of cement may be required to cater for inadequate and/or non-uniform mixing of the concrete and to cater for the rough surfaces of the aggregate pieces being bound by the cement paste. Addition of any extra cement cannot make the concrete more durable. In case the mix is found to be non-workable for want of sufficient fines, an odd bag of pozzolanic powder may be added and/ or some plasticizer used. Since the concrete strength will be limited by that of the aggregate used, any lesser strength of the concrete can be achieved by adjusting the compaction suitably. Addition of extra quantity of cement will not do the trick of giving more strength and/or durability to the concrete, in case adequate control on W/C ratio and/or compaction of concrete could not be maintained.

 

Amongst the constituents of concrete only cement is a factory manufactured item and therefore susceptible to environmental attacks. Natural materials will always be superior and economical when compared with ‘manufactured’ replacements. Since cement has no intrinsic body and therefore strength, any quantity in excess of binding needs, is likely to make the layers between aggregate pieces thicker. Any exposed cement at the surface may get damaged due to environmental factors in addition. Amongst the constituents of the concrete cement is having the largest coefficient of shrinkage. This will ensure that the thicker cement layers will crack and loosen the aggregate pieces while facing changes of environmental temperature. This finally will result in deterioration of the monolith. Therefore, cement used in the concrete must not be in excess. Cement is factory produced, but its raw materials like lime-stone, clay etc are Natural minerals and therefore cement cannot be (and also is not) a product of identical chemical composition (even from adjacent batches). In short, every bag that one opens, needs field checks for characteristics of the cement before using the same. This makes it further costly.

 

Thus many defects in concrete may be developed after the structures are in use. This has led to development of construction chemical industry. They have developed chemicals to treat these defects. While treating the intended defects the reactive chemicals create some other side effects (defects?) in the concrete. As a result of all this the cement as a replacement of finely ground lime has become enormously costly and beyond the affordability of common man. Doubts are also cropping up if Cement is really an effective and acceptable replacement for freshly ground lime.

 

It will be apparent therefore that the New Material (cement) that was initiated (with much fanfare) to replace freshly ground lime is neither advantageous nor economical to anyone (at least in Indian environment) but to the manufacturers of Cement and construction chemicals. The structures constructed in Cement Concrete are non-durable, and cannot be made waterproof by human intervention Even Cement is not an environment-friendly material and its production as well as use add pollutants as well as heat to the atmosphere. The position in foreign countries is also not very good. The costly cement concrete structures need varieties of construction chemicals to add for getting desired results. Lot of technical consideration is needed to determine the type and quantity of the chemical to be mixed. The results are not of required durability or long lasting. The chemicals to be added are not inert and therefore dangerous to life and nature as well. Since however, the Westerners did not have any better method or construction material before cement, they may continue to insist on cement as ‘Best’ building material in use; let them. It is suggested that at this stage of development India should carry out checks on the utility of freshly ground lime against cement. Selection from the large variety of cements and additives in the market and the appropriate practices of complicated processes of designing, mixing, pouring, compacting as well as curing of concrete are confusing even to engineers and the construction is not economical to the consumer i.e. common man. Structures constructed with lime over 60 years ago appear to be still in serviceable state without undue maintenance expenditure. 

 

Cement is manufactured from mixture of lime stone and clay (both ground/crushed) in water (or dry if could be uniformly mixed). The slurry is blended to correct composition. This corrected slurry fed to rotary kiln heated by powdered coal is converted into clinkers. These clinkers ground in ball mill with addition of 2 to 3 % gypsum (for preventing flash setting). This cement is stored in cement silos for loading in bags or vehicles. The coal requirement of the rotary kiln is 350 Kgs per ton for wet process and 100 Kgs for dry process. Many factories produce cement by dry process but still some use wet process. Let us assume that on the average a ton of cement needs 150 Kgs of coal. 200 MT of cement (quantity produced and used in whole year of 2006) has used 30 million tons of coal. This would have added about 75 million tons of CO2 (Carbon-Dioxide) to the environment to increase the atmospheric temperature. Other countries in the world would have added lot more and thus earth temperature would have been raised to a very high extent. It is possible that this has been taken into account in Industry’s contribution to environmental pollution. It therefore can only be noted here as cement factory’s pollution portion. 

 

Once cement concrete is poured in formwork and starts hydrating, it evolves heat. Total heat that cement can generate during hydration is around 125 calories per gram of cement during its complete activity of hydration. This activity is a long drawn process and for our purpose we take 28 days hydration as full hydration for design purpose. A heat of hydration of 90 calories is given out by every gram of cement during that period. Let us consider that on the average 3 calories of heat is given out per day by one gram of cement. As per reports, in whole year India has consumed 200 million tons of cement during 2006 (or say, 17 million tons per month) for construction/repair of structures. Thus during the year 2006 concrete structures (only under construction/repairs) have given out 34 X 10*12 calories (or 34 trillion calories of heat) to atmosphere EVERY DAY!. More heat at a lower rate is being given out in balance period of the year in addition. This is during construction. Once the structures are in use, their exposed concrete bodies absorb heat from the sun during day and reject to the atmosphere during the evening is another aspect of heat evolution by concrete structures. India is considered to be (still) developing indicating that the use of cement is going to increase continuously as the ‘development’ progresses. Environment is getting heated to a large extent by the use of cement. Thus quite an appreciable quantity of heat is generated (for the environment) by cement consumed by all the nations; more by the developed Nations. Thus one can imagine how much heat is daily given out by the cement use to the environment so that earth temperature goes on increasing. It surely cannot be dismissed as minor aspect while considering the ‘Green- House’ effect on the earth due to human activities. 

 

It will be clear from above discussion that cement as building material has technical problems right from start and could not yet been completely rectified. Rather they appear to be increasing continuously. People using it have perforce to add some (more expenditure?) chemicals to overcome the defects. Similar to modern system, an attempt to rectify some defect creates another one in concrete structures as well. In addition, this material requires lot of energy during production process and adds heat and pollution to the environment while in use. It is thus creating havoc all over the world. Actually, Kyoto round of WTO talks during Nineties could have done better by adding ‘scrapping of this material from production (as well as use) slowly’ to its suggestions for corrective measures to reduce rising temperature of the earth. 

While discussing this aspect with my friends most of them agreed with the view that cement is surely a building material quite inferior to burnt and ground lime. However, they did insist on telling that the lime is incapable of constructing highrise buildings for which cement concrete is only available. Use of cement therefore can immediately be stopped only for buildings lower than 3 stories high. Quite a large amount of pollution can be reduced by use of this rule since only a fraction of buildings are presently highrise structures. This should be immediately implemented. 

 

If we consider the condition of man on this planet since he came, it will be apparent that getting way from Nature’s contact and desire to abjure physical labor are the two tendencies of man which are detrimental to him. Lack of physical labor has made him fall sick frequently for lack of exercising his body adequately and properly. Distance from Nature has kept him away from Nature’s ways to prevent/recover from various mental as well as physiological illnesses. When man stays in highrise buildings he is necessarily away from earth i. e. Nature and he misses all the advantages of it. Therefore, as a rule man need not operate from high rise structures at all. Therefore, he could have done nicely with burnt & ground lime as construction material and avoided manufacture and use of cement at all. All the pollution of environment as discussed above could have been avoided. Now as well disusing this material he can reduce environmental pollution. He will have to use lime as a new building material instead. In old world at least, he will have few persons familiar with it to help him in this aspect.

 

Mr Joseph Aspdin, a Leeds constructor took a patent for Portland cement {a fine powder of certain earth crust found in nature which was similar to the rock at Portland (a place in England) in color in 1824. Its use in Europe started in right earnest since they had no other (suitable) construction material prior to that time. As good traders they propagated with zeal and force this material in their colonies. The slave population had no choice to refuse it (though they had better material in ‘finely ground lime’) for masonry. During their rule British always discouraged the use of any indigenous materials or systems like Dhaka Mulmul, Handloom weaving, Ayurved and Gurukul System of learning in India and offered their imported versions instead, specifically to kill the indigenous systems and fleece the riches of the enslaved country and people. Same thing happened concerning use of lime in construction during their rule. This led to disuse of lime slowly till WWII, after which it nearly reached its extinction as a building material. As a young boy, I remember to have seen the use of ‘Ghaani’ being used for grinding lime by bullock when our house at Satara was being extended in around fifties (about 55 years ago) as an only instant.

 

It is quite likely therefore that some oldies aware about use of this material may still be around and can assist us in redeveloping it into a building material superior to Cement in all aspects. The organization of IITians that is coming up in India to develop technical education (and other aspects) Nationwide can do well to serve the World if they can revive the ‘finely ground lime’ as a building material to replace the ‘dirty’ cement. The world will be saving not only money and energy but it will be saving the environment and Nature as well for our future generations. This will really be going back to the (progressive) future!

 

Reference

 

1. Minimum Cement Content for Strength and Durability of Concrete– Technical Rationale’ by Prof M D Apte published in NBM & CW Jan 2002.

 

2. Cement concrete text book ‘Concrete Technology’ by Prof M. S. Shetty.

 

3. Indian Standards concerning Concrete Construction as brought out by BIS

 

4. Cement Manufacturers Literature and publications

 

5. Experiences of the author during his professional career

 

6. British rulers’ efforts in imposing Western culture

 

Addition from Editor

 

Gangaccanal aqueduct known as Solani Bridge near Roorkee in Uttarakhand is a fine example of lime construction (Masonary line mortar) which is more than 150 years old by now with no problems. Large number of Arch Bridges on Ganga canal (constructed along Solani bridge starting at Hardwar are constructed using Bricks masonary in lime mortar.