Influence of Hydrated Lime on the Chloride-Induced Reinforcement Corrosion in Eco-Efficient Concretes Made with High-Volume Fly Ash

Abstract

The main objective of this study was to analyze the influence that the addition of finely ground hydrated lime has on chloride-induced reinforcement corrosion in eco-efficient concrete made with 50% cement replacement by fly ash. Six tests were carried out: mercury intrusion porosimetry, chloride migration, accelerated chloride penetration, electrical resistivity, and corrosion rate. The results show that the addition of 10–20% of lime to fly ash concrete did not affect its resistance to chloride penetration. However, the cementitious matrix density is increased by the pozzolanic reaction between the fly ash and added lime. As a result, the porosity and the electrical resistivity improved (of the order of 10% and 40%, respectively), giving rise to a lower corrosion rate (iCORR) of the rebars and, therefore, an increase in durability. In fact, after subjecting specimens to wetting–drying cycles in a 0.5 M sodium chloride solution for 630 days, corrosion is considered negligible in fly ash concrete with 10% or 20% lime (iCORR less than 0.2 µA/cm2), while in fly ash concrete without lime, corrosion was low (iCORR of the order of 0.3 µA/cm2) and in the reference concrete made with Portland cement, only the corrosion was high (iCORR between 2 and 3 µA/cm2).

Machine Learning Method to Explore the Correlation between Fly Ash Content and Chloride Resistance

“…Consequently, increasing the fly ash admixture and the inclusion of Al 2 O 3 effectively enhance the chloride binding capacity of fly ash concrete and slow down the degradation caused by material corrosion. The surface hydration products (C 3 A, C 4 AF, C-S-H) bind to free chloride [ 60 ], effectively controlling the reduction of free chloride content in fly ash concrete systems [ 61 , 62 ].…”

“…Consequently, increasing the fly ash admixture and the inclusion of Al 2 O 3 effectively enhance the chloride binding capacity of fly ash concrete and slow down the degradation caused by material corrosion. The surface hydration products (C 3 A, C 4 AF, C-S-H) bind to free chloride [60], effectively controlling the reduction of free chloride content in fly ash concrete systems [61,62]. The reason why the chloride resistance of fly ash concrete becomes more prominent in later stages is due to the presence of dense spherical vitreous microspheres on the surface of fly ash particles.…”

The impact of calcium hydroxide addition on HVFA mortar and concrete properties

“…Thus, the addition of external calcium hydroxide could be necessary [19]. Produced from the calcination of calcium carbonate and converted into calcium hydroxide by the slaking process, calcium hydroxide is a strong alkaline often used as an additive for fly ash mixes [20][21][22][23]. It can also be used in the form of lime water [24][25][26].…”