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 CO 2 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.

Effect of coupled deterioration by chloride and carbonation on chloride ions transport in concrete

“…In the second stage, the specimens were prepared according to [14]: the lateral and bottom faces were painted with paraffin (type 1) or epoxy resin (type 2), the unique free face was used to allow a unidirectional flux during the exposure time. In the third stage, the specimens were wrapped with plastic film and put in an oven (40 ºC), for 20 days, to distribute the internal humidity.…”

“…She believes that this behaviour is related to carbonation depth reached. The lack of standardisation about the various parameters involved in the experimental work such as type of test, temperature, humidity and concentration of NaCl and CO 2 makes it difficult to compare these results [14].…”

The Efficiency of Fly Ash Concrete in the Context of the Combined Action between Chlorides and Carbonation

“…The chemical composition of FA was determined using x-ray fluorescence spectroscopy. In addition, Scanning Electron Microscopy was used to observe FA morphology (Figure 1), revealing that it is mainly composed by cenosphere particles (Malheiro et al, 2018). These FA were obtained from the burning of South African and Colombian coal in Portuguese thermoelectric power plants.…”