Factors Affecting Strength of Clays in the Temperature Range 110° to 800°C

Using a carefully established procedure for the preparation of test bars and for the measurement of the modulus of rupture, the effect of firing temperature on the transverse strength of a Georgia kaolin, Kentucky ball clay, and Missouri fire clay was determined. The kaolin showed the greatest temperature vs. strength sensitivity (-19% to +50% of the dry strength); it therefore was used in a study of the effect of aging, electrodialysis, and ion exchange on strength-temperature relationships. Kaolin treated with H₂O₂ and HC1, and electrodialyzed kaolin with NaCl and CaCl₂, was weaker than the untreated clay after being fired at temperatures below 650°C. but was as much as 131% stronger at 800° firings.