Effect of Air Entraining Agents on the Long Term Drying Shrinkage of Glazed Hollow Beads Thermal Insulation Mortar

Abstract:

The drying shrinkage of glazed hollow beads thermal insulation mortar after two years was measured by vertical length comparator, and influences of air entraining agents of different contents (0%, 006%, 012%, 018%, 024%, by mass) on the long term drying shrinkage were investigated, water loss was measured by weighting method and pore structure was characterized by nitrogen adsorption/desorption method, the correlation among them was researched. The results show that drying shrinkage process includes three steps according to curing time extension: the acceleration period (before 7d), the deceleration period (7365d) and the metastable period (after 365d). There is no change in the development trend of drying shrinkage of mortar with addition of air entraining agents. In three steps in the curing time, the drying shrinkage at the last two stage is greatly restrained. The drying shrinkage of mortar in the first stage increases quickly owing to the fast dehydration, but its development in the last two stages is due to pore volume of mortar with radius less than 500nm, especially the increase of pore volume fraction of the pore radius within the size range of 73nm to 123nm. Effect of air entraining agents is proportional to its use level, there is no more effect with too large content of air entraining agents on drying shrinkage owing to lack of air entraining effect.