Abstract
Concrete possesses an intrinsic chloride binding capacity. Chloride ions from the environment bind with the hydrated cementitious phases in the form of bound chlorides. The contribution of chemically bound chlorides toward increasing the service life of concrete structures is vital as they help in slowing down the chloride diffusion in the concrete thereby delaying reinforcement depassivation. The authors attempt to increase the chloride binding capacity of concrete by adding a small amount of Mg–Al–NO2layered double hydroxides (LDHs) with the objective to delay reinforcement corrosion and by this to considerably extend the service life of concrete structures situated in harsh environments. This study presents numerical and experimental analysis of the action of LDH in concrete. Formation factor is used to determine the effective chloride diffusion coefficient. In addition, the chloride binding isotherms together with Poisson–Nernst–Planck equations are used to model the chloride ingress. A comparable chloride binding is observed for concrete with and without Mg–Al–NO2, depicting only a slight chloride uptake by Mg–Al–NO2. Further investigations are conducted to understand this behavior by studying the stability and chloride entrapping capacity Mg–Al–NO2in concrete.
Highlights
Concrete structures are prone to reinforcement corrosion induced damage due to chloride ingress.[1,2] Chloride ingress occurs in infrastructures exposed to the marine environment, or due to the action of deicing salts in structures along roadways.[3]
We investigated the use of layered double hydroxides (LDHs) for additional chloride capture in concrete
Deviations in predictions especially in the first few millimeters along the penetration path can be attributed to many factors: first, the occurrence of skin effect[49,50,51] causes a sharp chloride peak in the first few millimeters; second, the model is sensitive to the variability in the chloride binding isotherm and the fact that formation factor was measured at 28 d age, whereas the chloride profiles were measured after 46 days of exposure time
Summary
Concrete structures are prone to reinforcement corrosion induced damage due to chloride ingress.[1,2] Chloride ingress occurs in infrastructures exposed to the marine environment (offshore or costal structures), or due to the action of deicing salts in structures along roadways.[3]. One of the recently developed nanocontainers of Mg–Al–NO2 layered double hydroxides (LDHs) are used as chloride binding additives inside concrete. Concrete mixed with LDH could show improved chloride binding capability and controlled corrosion inhibitor release. This property has been termed as “selfprotection” of reinforced concrete in the LORCENIS project. Chloride transport was modeled in water-saturated concrete using the Nernst–Planck equation and combines information from FF c and chloride binding isotherms.[31] The transport of charged ions through the pore network gives rise to a potential field which is accounted via the Poisson’s equation.[32] The resulting coupled system of equations was solved using the finite element method[33] for a 1D domain. The article highlights the stability of LDH in cementitious environments to explain the reduced chloride uptake by Mg–Al–NO2 in the cementitious matrix
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