Behaviour of cementitious matrices subjected to the combined action of chloride ions and carbonation

Abstract

Carbonation and chloride action are the two leading causes of degradation in reinforced concrete structures.
Despite the combined action of these two mechanisms being a reality, there is little research on the effect of
this combination in cementitious matrices. Furthermore, the incorporation of fly ash in cementitious matrices
has been frequently used in order to make the matrix more resistant to the action of chlorides. On the other
hand, it is known that Ca(OH)2 existing in the matrix is consumed by the pozzolanic reactions, which makes
easier the carbonation front advance. Therefore, this paper presents a study of the behavior of cementitious
matrices, with and without fly ash, subjected to the combined action of chlorides and carbonation. Two different
kinds of mortars were produced: reference (only cement CEM I 42.5R) and fly ash mortar (40% replacement
of cement). After curing, the specimens were subjected to three different wetting-drying cycles,
considering NaCl solutions and CO2 atmospheres. Afterwards, chloride profiles and carbonation front were
measured. Results show that carbonation has a direct influence on chloride penetration, decreasing it for cement
mortars with 0% fly ash and increasing it for mortars with 40% cement replacement by fly ash. Moreover,
the evolution of carbonation is also influenced by chloride presence, which decreases under the combined
action.
Keywords: Chloride; Carbonation; Mortar; Fly ash; Wetting-drying cycles.