Examination and interpretation of Portland cement clinkers by microscopy as an aid to process control

Abstract

Microscopy has proven to be a relevant method in the elucidation of problems that occur during Portland cement clinker manufacture. In addition to describing the basic Portland cement clinker manufacturing processes, the thesis sets out the laboratory methods for sample preparation and microscopic examination. The raw materials and cement clinkers were examined using a variety of microscope techniques and the features observed described. Microscopy of Portland cement clinker has only been used in South Africa to a limited extent and this was the first systematic investigation to characterise both the raw materials and the resultant Portland cement clinker by microscopy means. The advantage to the manufacturing industry is that the quality of the end product can be improved. The quality of the cement clinker is determined by various factors such as the raw feed composition, fineness and homogeneity, and the kiln burning and cooling conditions. Microscopic examination was carried out to analyse the kiln feed, to evaluate powder mounts of cement clinker according to the Ono method and to interpret the microstructures observed in polished sections. The quality of the cement clinker can be improved in many instances if attention is paid to details of the microscopic examination and appropriate action taken to change the manufacturing process based on the results of the examination. Two case studies are discussed to demonstrate the practical application of cement clinker microscopy. In the one study, the quality of cement clinker can be improved by carefully controlling the fineness of the kiln feed. In the other study, microscopy assisted in the selection of alternative raw materials for cement clinker manufacture. The case studies have shown that theoretical knowledge gained in the study of South African cement clinkers and numerous overseas samples has been used in a practical environment to improve the quality and consistency of cement clinker. Cement clinker microscopy has a major role to play in the quality control of the cement manufacturing process. Cost savings can also be affected through cl inker microscopy. For it to be used to optimal benefit, microscopic examination should take place on a regular basis, i.e. daily or on a shift basis.