Cement Energy and Environment

today's concrete relates to the timing, duration, and type of curing , and the balance between curing time and speed of construction. Still another issue is the knowledge gap among many practitioners with regard to the properties of individual concrete ingredients, how the various ingredients interact in the concrete mixture, and how to arrive at the optimum mixture for the type of application and level of exposure to adverse environments. An effective technology transfer plan is needed to convey to practitioners state-of-the art information and the latest research findings on materials and concrete properties_. Current testing methods for concrete and its ingredients are another challenging issue. Some of these methods are simple but time-consuming and tend to slow the pace of construction . New or improved tests for determining the properties of Technologies from other fields, such as medicine or the military that can be nonintrusive should be considered . Courtesy: Civil Engineering & Construction Review, Vol.24, January 2011, P10. MORE UNCOMBINED CLINKER This article first appeared in International Cement Review in March 2011 and is reprinted with kind permission of Tradeship Publications Ltd, United Kingdom. Email: info@CemNet.com Website: www.CemNet.com Dr. Clark completes the account of the mystery of uncombined clinker on a Middle Eastern cement factory and reveals that similar problems are being l!ncountered elsewhere. Knowledge and understanding of cement kiln chemistry is vital to explain or find solutions to these problems. Knowledge and understanding that is provided by the CemNet Cement Kiln Chemistry course. Dr. Clark, ICR Research Regular readers will recall the peculiar case of the uncombined clinker from the June 2010 issue of International Cement Review. The Technical Forum moderator had been contacted by an old colleague, who was a technical manager for a major Middle Eastern cement company. The technical manager's problem was that his current company had switched the firing of its kilns from natural gas to coal and was now encountering the problem of high free-lime clinker whenever the lime saturation factor rose above 93.5 per cent. When the kilns were fired with natural gas there was no problem combining the clinker when the lime saturation factor was 96 per cent or above. What could be the possible cause of this high free– lime clinker problem? The moderator went through a process of elimination on the likely causes, including whether the ash content of the coal was being correctly adjusted for, whether the chemistry of the clinker had changed significantly a11d whether there was now that was preventing the clinker from being combined and affecting the stoichiometric balance between alkalis and sulphate. The technical manager was able to confirm that alkalis had fallen and sulphate had risen , meaning that the stoichiometric bal~mce had improved if anything. Alkalis in clinker were low enough to produce low-alkali cement. None of these cou ld be the cause of the difficulty in combining the clinker. The moderator then thought that just because the alkalis and sulphate were in balance in the clinker did not necessarily mean that they were in balance in the hot meal. What were the levels in the hot meal? Bingo! The alkalis were concentrating up in the hot meal by the expected 2- 3 times, while the sulphate was present in concentrations some 20 times that found in the clinker. This must mean that some sulphate was present as calcium sulphate in the hot meal, which could then break down in the burning zone to produce free lime, sulphur dioxide and oxygen: CaS0 4 +-+ CaO + S02l + 1/2021 In this breakdown the free lime would be formed so late in the process that there was insufficient time for combination with c 2s to form c 3s. leaving the clinker containing high levels of uncombined, free lime. 4