Theoretical and Experimental Models to Evaluate the Possibility of Corrosion Resistant Concrete for Coastal Offshore Structures

Abstract

This study built theoretical and practical models to evaluate the corrosion resistance of concrete for coastal offshore structures in Vietnam. A mathematical model was developed in the form of a system of nonlinear partial differential equations characterizing the diffusion “free calcium hydroxide” in a solid of a concrete structure. The model describes the process of non-stationary mass conductivity observed in the “concrete structure—marine environment” system under non-uniform arbitrary initial conditions, as well as combined boundary conditions of the second and third kind, taking into account the nonlinear nature of the coefficients of mass conductivity k and mass transfer β. It was shown that the solution of the boundary value problem of non-stationary mass conductivity allows us to conclude about the duration of the service life of a concrete structure, which will be determined by the processes occurring at the interface: in concrete—mass conductivity, depending on the structural and mechanical characteristics of hydraulic structures, and in the liquid phase—mass transfer, determined by the conditions of interaction at the interface of the indicated phases.

An Engineering Method of Analyzing the Dynamics of Mass Transfer during Concrete Corrosion Processes in Offshore Structures

“…The boundary problem of mass conductivity in a two-layer plate is addressed and solved in [ 11 , 12 , 35 ]. The general statement of the nonstationary mass conductivity problem for an unlimited model plate can be formulated as follows: for an enclosing structure: …”

“…When analyzing the data extracted from the sources [ 11 , 12 ], a researcher should pay attention to the composition of the chemical components of seawater in the nearshore area. The concentration of ions is 2.5–3.02 kg/m 3 in seawater with a salt content of 33–35 kg/m 3 , which is explained by the dissolution of sulfate compounds of Ca, Na, K, and Mg, same as in fresh water, but in much larger amounts and with a predominance of sodium and magnesium salts.…”

“…The mechanism of sulfate corrosion is characterized by diffusion (mass conductivity) of free calcium hydroxide (Ca 2+ ions) from the volume of the concrete matrix through the “concrete–soil” interface, followed by mass conductivity through the soil layer to the “soil–liquid” interface, and mass transfer into the marine medium [ 3 , 6 , 11 , 12 ].…”

“…The mechanism of chloride corrosion is much more complicated [ 3 , 11 , 12 ]. Diffusion of chloride ions results from mass conductivity through the product layer.…”

“…Both soluble compounds like CaCl 2 and insoluble compounds like Mg(OH) 2 are formed in the soil layer. CaCl 2 ions are carried into the aquatic medium, while Mg(OH) 2 triggers pore colmatation [ 3 , 11 , 12 ]. Mass transport of active components in furtherance of the above corrosion mechanisms can be determined with differential equations of nonstationary mass conductivity (diffusion in a solid body) [ 20 , 21 , 22 , 23 ].…”