The normal purpose of this examination is to assist in cement quality control by evaluation of the clinker and raw feed composition, particularly in certain size fractions, and to determine the general characteristics of the burning process, including the rate of heating, maximum temperature, time at high temperature, cooling rate, and other features. Microscopical examination is particularly helpful with samples representing before and after equipment or materials changes. Powder mounts, polished sections, and thin sections are routinely examined.
Cement and clinker samples are treated with a potassium hydroxide-sugar solution to concentate the silicates to facilitate their observation in transmitted light. If applicable, a 28-day mortar-cube strength will be predicted using a modified Ono table and equation (1995).
Because of the close correlation between raw feed characteristics and clinker microstructure, the feed is also studied in thin section (20 to 25 microns thick) or grain mount, emphasizing the >45-micron siliceous particles, >125-micron limestone grains, and the acetic-acid insoluble residue which may contain dolomite, slag, fly ash, and minerals. Grain counts of raw feed mineralogy to establish C125, Q45 and AK, according to F. L. Smidth's burnability equation are determined.
For raw feed, clinker or cement examination 300-gram samples of each are recommended. The clinker sample should be taken just downstream from the cooler to restrict the number of kiln variations that might be recorded in the clinker and thus simplify the interpretation. In oil-well cements particular attention is given to silicate crystal characteristics, agglomerations, and free lime in the 100- to 200-mesh fraction.
A report illustrated with color photomicrographs will be prepared covering the principal findings and conclusions. A color audio-video tape can be supplied in place of photomicrographs; the tape is particularly helpful in presenting the microscopical findings to those not familiar with microscopy and to illustrate the variations in the samples. Petrographic examinations of quarry ledge rocks (crushed to 5.0 mm) and other individual raw feed components are highly recommended.
Turnaround time is approximately two to three weeks, depending on the number of samples and workload.