Carbonation transport through concrete

The influence of temperature and humidity affect the corrosion rate through their influence on the electrochemical reactions at the steel/concrete interface and through their influence on ion transport between anodes and cathodes. Although the mechanisms are not fully understood, it appears that the concrete resistivity (or conductivity) is strongly related to the corrosion rate at moderate or low temperature [35-38]. Variation in resistivity due to variation of humidity (at constant temperature) caused an inversely proportional variation of corrosion rate in carbonated mortar and concrete with low amounts of chloride or without chloride. Variation of temperature (at constant humidity) caused a similarly varying corrosion rate. 

In hardened cement-based composites the transportation of liquids and gases through pore and microcrack systems plays a very important role in many processes, such as hydration of Portland cement, pozzolane effects of microfillers, carbonation, corrosion of cement paste and reinforcement due to reaction with external agents, shrinkage and creep, etc. These processes are partly described in respective Sections 4.1, 4.3, 6.5 and 11.5. Only basic information is reiterated below concerning the flow of liquids and gases through concretes and mortars. 

A migrating inhibitor with no pretensions of volatility is MFP or monofluorophosphate. This relies on capillary action other transport mechanisms to get the material down to the steel through the concrete cover. A recent paper showed that it could be quite successful in carbonated concrete Raharinaivo and Malric (1998). Calcium nitrite has also been offered in a formulation for patch repairs or overlays with the intention that the nitrite will diffuse out of the patch and protect the steel. 

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