Influence of aging conditions upon the properties of calcined clay and its performance as supplementary cementitious material

The investigation aimed at determining a possible impact of various aging conditions on calcined clays and their performance as supplementary cementitious material (SCM). Two calcined clays were exposed to six different aging conditions. Chemo-mineralogical and physical parameters were measured to reveal possible changes. Aging of calcined clays at high relative humidity or in 3% CO2 atmosphere resulted in a higher specific surface area and an increased water demand. This was in part due to the formation of calcite and gypsum. The latter promoted the development of heat of hydration. The aging of calcined clays itself had negligible influence on fresh mortar properties and no clear effect on strength of mortar made with these SCM. Nonetheless, most flexural and compressive strength values of mixes containing 20% aged calcined clay were higher than the reference mixes made with cement only.