MECHANISM OF EXPANSION IN HARDENED CEMENT PASTES WITH HARD-BURNT FREELIME

The expansion characteristics of hard-burnt free lime in cement pastes were determined by measurements of free linear length changes in vari ous periods. Hydration of lime in water and in alkali solutions was in vestigated to evaluate the influence of OH- ions on the migration of C a2+ ions from lime, the supersaturation of solutions for Ca(OH)(2) and the size as well as the dispersion of distribution of Ca(OH)2 crystal s formed. Based on the experimental results, an expansion mechanism of hydrating lime in cement pastes was proposed. It is found that OH- io n in pore solutions may force Ca(OH)(2) to form in situ and promote th e development of expansive forces. The expansion of hydrating lime is caused by the crystallization of Ca(OH)2 crystals formed in situ.