Control of Crystal Polymorphism of CaCo3 Generated in Cracks of Cementitious Material by Change of Temperature and pH by
Generally, crack is inherent in
reinforced concrete structures and leads to serious damage in service period.
In there, recurrences of such damages will lead to the enlargement of the
cracks, thereby allowing other deteriorating elements such as CO2 and Cl- to further penetrate the
concrete, and this can have serious consequences for the concrete structure. On
the other hand, in an environment where there is supply of water, concrete
structures display “self-healing,” in which some of cracks close up naturally, and
this phenomenon is closely associated with the hydrates that are newly
generated in the areas of crack formation. In this study, author aimed to the
kind of CaCO3
generated by self-healing
phenomenon. CaCO3 is
crystal polymorphism and it’s reported that crystal form can be controlled by
the relationship of temperature and pH. Generally, CaCO3 consist of the three kinds such as
calcite, vaterite and aragonite for crystal formation. A vaterite is also
generated most densely among these, and self-healing can be expected. Therefore,
an experiment is made for the purpose of establishing the condition to generate
a vaterite. The supplied a saturated Ca(OH)2
solution with CO2 nano-bubble is used for the
effective self-healing. Conditions of the temperature and pH are managed by 20-60°C
and 8.5-12 pH. As a result, it was confirmed that the self-healing conditions
of saturated Ca(OH)2 solution,
which supplied CO2 nano-bubbles,
displayed the most effective self-healing performance in the surface and
internal sections of the cracks.
