Effect of fly ash on drying shrinkage of thermal insulation mortar with glazed hollow beads

Drying shrinkage of thermal insulation mortar with glazed hollow beads was measured by a vertical length comparator, and the influences of fly ash with different contents (0, 18%, 36%, and 54% were used) on the long-term drying shrinkage were discussed. The mass loss was measured by the weighting method and the pore structure was characterized using three different methods, including the light microscopy, the mercury intrusion porosimetry (MIP), and the nitrogen adsorption/desorption (NAD) experiments, and the correlations among them were researched. The results show that drying shrinkage process of thermal insulation mortar includes three steps with increasing curing time: the acceleration period (before 7 d), the deceleration period (7-365 d), and the metastable period (after 365 d). Drying shrinkage in the first stage (7 d before) increases quickly owing to the fast water loss, and its development in the last two stages is attributed to the increment of the pore volume of mortar with the radius below 50 nm, especially the increment of the pore volume fraction of the pore radius within the size range between 7.3 nm and 12.3 nm. There is no change in the drying shrinkage development trend of mortar with fly ash addition, and three steps in the service life, but fly ash addition in the mortar restrains its value. There is a linear relationship between the drying shrinkage and fly ash content, which means that drying shrinkage reduces with fly ash addition.