Cement, Energy and Environment

I would impair the workabil ity of concrete mix and affect concrete quality if there is delay in pouring concrete. What the user actually means by setting time is hardening time. Very often, the sales people mistake setting time for hardening time. Some consumers want rapid hardening cement. Myth-3: "Rapid hardening cement is good, as construction work can Nowadays, 53-grade cement 1s very popular among builders because it develops strength very fast and construction time is reduced. Is it desirable to supply rapid hardening cement to the consumers? Rapid hardening cement is rich in lime and evolves very high heat of hydration when mixed with water thereby causing micro cracks in the concrete structure. The durability of concrete is affected due to these micro– cracks and life of concrete is reduced. Secondly the precious limestone reserves of earth are depleted fast in making high early strength cement. High lime cement emits more C0 2 into the atmosphere and. consumes more energy during manufacturing . Many developed countries have imposed environmental tax for emitting greenhouse gas li ke C0 2 into the atmosphere. Apart from the guilt of polluting the atmosphere, the producers of such cement would also have to bear the environmental tax burden in these countries. Actually the cement producers should encourage consumers to use blended cement instead of OPC for normal building construqtion , which would help to conserve scarce limestone reserves, evolve less heat during hydration thereby improve concrete durability and reduce C0 2 emission during manufacturing. Rapid hardening OPC cement should be used only for special applications. Myth-4: "Very Fine cement gives good strength and surface finish" Some consumers want fine-ground cement thinking that fine cement would give good strength and good surface finish for concrete. Some producers grind the cement very fine to improve early- strength of cement though later-strength development may not be appreciable if the clinker quality is bad. They cover up the weakness of poor quality ' . • ~ ,. #> ~· . . .... • • I' • ..41 . ; clinker by grinding the cement finer. The other producers are also compelled to grind the cement finer because of the competition . The customer is misguided into buying this cement because his choice is for high early– strength cement. The concrete is supposed to gain strength slowly for many years for better durability. After quickly attaining near-full strength in short time, fine-ground cement would be prone to deterioration only, in later times. Considerable energy is wasted in grinding the cement finer to achieve no significant benefit. Myth-5: "Some brands give more cement in bags than others" Bags of some cement brands look big as though having more volume of cement. This makes the customer to think that he gets more cement from these brands. It is another deception. Bags of all cement brands weigh 15