Although the equations governing the individual basic physical processes involved in freezing and thawing of concrete are known, a mathematical model for this complex phenomenon is unavailable. Its formulation is attempted in the present study. Desorption and absorption isotherms for concrete below O°C are constructed on the basis of isotherms for concrete above O°C, using pore size distribution functions. Water movement during freezing or thawing is described as a double diffusion process, involving both macroscopic diffusion through concrete and local diffusion of water into or out of air-entrained bubbles. Heat conduction is formulated taking into account the latent heat of freezing. Pore pressures are used in a two-phase material model, which makes it possible to predict the stress in the solid structure of concrete caused simultaneously by freezing and applied loads. This in principle reduces the freeze-thaw durability problem to the calculation of stresses and strains. However, development of the model to full application would require various new types of tests for calibration of the model, as well as development of a finite element code to solve the governing differential equations. Such a mathematical model could be used to assess the effect of cross-section size and shape, the effect of cooling rate, the delays due to diffusion of water and of heat, the effect of superimposed stresses due to applied loads, the role of pore size distribution, the role of permeability, and other factors which cannot be evaluated at present in a rational manner.

The scarcity of good aggregate in Japan led to an investigation of the use of a corrosion inhibitor for reinforced concrete. Corrosion current measured on small test specimens soaked in limewater for one day with an impressed voltage of + 400 mV with respect to the saturated calomel electrode shows that the introduction of calcium nitrite diminishes the corrosion of reinforcing steel in the presence of admixed sodium chloride. Long-term tests on larger specimens partially immersed in saturated sodium chloride solution indicate that admixed calcium nitrite can prevent the open circuit potential of reinforcing steel from entering the active region. Calcium nitrite was found to enhance the strength of concrete. Calcium nitrite complies with the requirements of ASTM Specification for Chemical Admixtures for Concrete (C 494-71). The use of a calcium-based admixture is expected to sidestep the issue of alkali-aggregate reactions and subsequent deterioration of concrete.

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Reinforcing steel in portland cement concrete is subject to accelerated corrosion in the presence of chloride ions. A corrosion-inhibiting admixture based on calcium nitrite has been shown to confer protection (that is, to inhibit corrosion) if the chloride to nitrite weight ratio (Cl−/NO2−) does not exceed 1.5. Visual observations made on rebars in limewater solutions containing chloride and nitrite ions, current and potential measurements on concrete cylinders with embedded reinforcing bars (rebars), and potential measurements on simulated concrete bridge decks were in substantial agreement.