Corrosion protection of steel embedded in cement-stabilised rammed earth

Cement-stabilised rammed earth (CSRE) reinforced with steel is a modern adaptation of an ancient construction technique, permitting the use of a wider range of structural forms and applications than those used traditionally. However, corrosion behaviour of embedded steel in CSRE is not yet understood, casting doubt on the longevity of these structural solutions. In this paper, we assess the ability of a range of CSRE mixes stabilised with 10% cement to protect embedded steel using electrochemical measurements, considering also material alkalinity, carbonation resistance and capillary absorption. Results demonstrated that the pH of the CSRE mixes was sufficiently alkaline to provide the appropriate environment for passivation of steel reinforcement. Corrosion initiation via water-borne aggressors was also found to be unlikely as CSRE sorption rates were comparatively low, so that the initiation phase for corrosion progression was predominantly controlled by carbonation; carbonation would most likely have reached the reinforcement within approximately 5-15 years (50 mm cover) or 30-75 years (150 mm cover), likely depassivating the reinforcement within the design life span. We demonstrated that a corrosion potential of 200 mV SCE indicates conditions of negligible corrosion of steel in CSRE. As behaviour varied little between the four tested soil mixes (of varying granularity), it is reasonable to expect that findings presented here also apply to other soil mixes stabilised with 10% cement.