2011 Volume 65 Issue 1 Pages 282-289
Carbonation is known as a deleterious phenomenon for concrete structures. On the other hand, however, it can have some positive consequences to concrete. It results in increases in surface hardness and strength of concrete so that the surface zone of carbonated concrete acts as a protective layer against penetration of harmful species. Furthermore, carbonation has been revisited recently because it is a fundamental function of self-healing in concrete. Such a positive effect of carbonation on properties of concrete is accompanied by changes in porosity and pore size distribution of the surface zone of concrete. In this study, in order to investigate changes in permeability due to carbonation at early ages, the electrical conductivity test and the SEM-BSE image analysis were carried out for cement pastes and concretes that were exposed to an accelerated carbonation condition. The pastes specimens were subjected to the carbonation environment immediately after demolding. The concrete specimens were stressed until the tensile stress/strength ratio of 50％ at 7days. Then, those damaged specimens were cured under the accelerated condition. When they were exposed to the accelerated carbonation at early ages, loss of water was reduced. Degrees of hydration of cement in the carbonated specimens were comparable to those in specimens cured continuously in water. Electrical conductivities of the cement pastes and the damaged concrete were also comparable to those cured in water. Dense surface zone formed by carbonation prevents water from evaporating even in a relatively dry condition. This led to further hydration so that the porosity was decreased and the induced microcracks were healed.
