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Chemical and Physical Interactions between Chlorides and Cement Hydrates
Published in Shi Caijun, Yuan Qiang, He Fuqiang, Hu Xiang, Transport and Interactions of Chlorides in Cement-Based Materials, 2019
Shi Caijun, Yuan Qiang, He Fuqiang, Hu Xiang
The stability of Friedel’s salt is of great important for chloride binding of cement-based materials; the dissolution of Friedel’s salt can release chloride ion into pore solution. Hassan (2001) investigated the stability of Friedel’s salt and found that it was highly dependent on the chloride concentration in the surrounding solution. When chloride concentration decreased, Friedel’s salt in the system could decompose into Kuzel’s salt. It was also reported (Thomas et al. 2012) that Friedel’s salt can be formed in cement paste when immersed in high concentration NaCl solution. As shown in Figure 3.5, as the chloride concentration decreased, the content of Friedel’s salt detected by XRD gradually decreased and a new compound which may be Kuzel’s salt was detected. Balonis et al. (2010) studied the effects of chloride ions on mineralogy of hydrated Portland cement systems, and proposed the schematic phase relation at 25ºC between Friedel’s salt and other AFm phases shown in Figure 3.6. It can be seen from the figure that most of composition ranges were dominated by two solid phases of SO4-AFm and Friedel’s salt. Kuzel's salt can be destabilised at very small amounts of carbonate and will only be encountered in low-carbonate environments.
The Chemistry of Concrete Biodeterioration
Published in Thomas Dyer, Biodeterioration of Concrete, 2017
AFt and AFm phases containing the formate ion have also been reported and characterized in terms of their structure [38]. Whilst solubility data for these phases is not available, it is likely that behaviour comparable to that seen for sulphuric acid is probable.
Characterization of lime-stabilized earthen mortars from historic masonry structures
Published in Claudio Modena, F. da Porto, M.R. Valluzzi, Brick and Block Masonry, 2016
M. Secco, A. Addis, G. Artioli
Both LOM_B and TOR_C samples are characterized by a mineralogical composition dominated by the silicate aggregate, while the determined calcite fraction is totally related to a partial carbona- tion of the employed aerial lime. Both samples are characterized by the occurrence of a relevant amorphous fraction, to be related both to a non-reacted fraction of paracrystalline clays intentionally added to the mix, and to the occurrence of amorphous calcium silicate hydrates (C-S-H phases, Richardson 2008). The occurrence of such phases is further confirmed by the presence of hydrated calcium aluminates (AFm phases, Matschei et al. 2007) within the analysed samples: such evidence clearly indicates a pozzolanic reaction between the calcic lime and the clay fraction employed for the manufacturing of the structural mortars.
Reliability of chloride testing results in cementitious systems containing admixed chlorides
Published in Sustainable and Resilient Infrastructure, 2023
Ahmed A. Ahmed, Naga Pavan Vaddey
Irrespective of type of cementitious system and source of chlorides (i.e., admixed or external), chlorides generally exist in either free state or remain bound to the hydration products. The amount of chlorides existing in each state is mainly dependent on the chloride binding capacity of the cementitious systems. For ordinary portland cement (OPC) systems, calcium silicate hydrate (CSH) and mono-sulfo aluminate (AFm) phases have been reported to mainly contribute towards chloride binding capacity by physical adsorption and chemical bonding mechanisms, respectively (Angst et al., 2009; Baroghel-Bouny et al., 2012; Florea & Brouwers, 2012; Glasser et al., 1999; Justnes, 1998; Larsen, 1998; Neville, 1995; Shi et al., 2017; Suryavanshi et al., 1996). The chlorides that are adsorbed on CSH can be either tightly or loosely bound depending on their location (i.e., surface vs. lattice). The chemical binding of chlorides by AFm or their analogous phases results in a class of products that are commonly referred by the term Friedel’s salt. Recent research has shown that chloride binding capacity can be significantly different for systems with admixed and external chlorides (Chang et al. 2019, Qiao et al., 2019; Trejo et al., 2019).
Chloride binding and desorption properties of the concrete containing corn stover ash
Published in Journal of Sustainable Cement-Based Materials, 2022
Mahmoud Shakouri, Christopher L. Exstrom, Guilherme D. Piccini
A previous study by the authors suggests that both acid- and water-washed CSA are reactive and promote pozzolanic reactions, leading to an increase in the strength and bulk electrical resistivity of concrete [29]. However, a knowledge gap remains regarding the influence of CSA on the durability properties of concrete. Given that most concrete structures are reinforced, the resistance and impermeability of concrete to the ingress of harmful species such as chlorides, which can lead to the corrosion of embedded reinforcing steel, is paramount. The rate and extent of ion transport in concrete is influenced by the physical properties of the concrete pore structure (i.e. pore size, pore connectivity, and tortuosity), and also the capability of cement hydrates, specifically C-S-H and AFm phases, to absorb and remove free chloride ions from the pore solution through physical and chemical binding [30–33]. Also, chloride binding products can alter the concrete pore structure (i.e. clog the pores) and reduce the chemical potential of a pore solution, which in turn can decrease the rate of chloride ingress in concrete [34]. It is widely accepted that the corrosion of embedded reinforcing steel in concrete can start when the concentration of free chlorides on the surface of reinforcing steel exceeds a critical threshold [35–37]. Thus, the capacity of a cementitious system to immobilize and bind free chlorides plays a vital role in reducing the risk of corrosion initiation and extending the service life of reinforced concrete structures.
Half-metallic ferromagnetism in cubic perovskite type NdInO3
Published in Philosophical Magazine, 2020
In fact, a, b, c, and d are the equilibrium fitted parameters and V is the volume of the unit cell. The (E-a) curves of the cubic oxide perovskite NdInO3 compound are illustrated in Figure 2 for paramagnetic (PM), ferromagnetic (FM), and anti-ferromagnetic (AFM) configurations. It is shown through Figure 2 that the ferromagnetic phase is the most favourable in energy with regard to the other PM and AFM phases, confirming that FM phase is the stable ground state of the cubic oxide perovskite NdInO3 compound. The optimised lattice parameters of the cubic oxide perovskite NdInO3 compound at the equilibrium such as, lattice constant (a0), bulk modulus (B0), its first pressure-derivative (B’), and minimum total energy (E0) are computed in all PM, FM, and AFM states and their values are reported in Table 1. Thus, the stable FM state of the cubic oxide perovskite NdInO3 compound is confirmed according to the 2×2×2 supercell calculations on FM and AFM configurations (see Figure 3).