Corrosion inhibition in concrete arising from its acid neutralisation capacity

It has been postulated that the most important inhibitive property of concr ete affecting the level of chloride required to initiate corrosion is its a bility to resist a Local fall in pH that might otherwise sustain passive fi lm breakdown at a developing pit. In this work a novel technique termed dif ferential acid neutralisation analysis was used to characterise this proper ty. It was noted that many solid phases in hydrated cement paste have pH de pendent dissolution characteristics that may strongly influence the pore so lution chemistry during corrosion initiation. While the important contribut ion made by calcium hydroxide has been widely recognised, other reactive hy dration products contribute more than 75% of the resistance to a pH reducti on to a value of 10. The resistance to a pH reduction (acid neutralisation capacity) to a value between 10 and 11 correlates reasonably well with the available chloride threshold level data. The inhibitive nature of the concr ete environment, characterised by its acid neutralisation capacity, depends on the cementitious binder, decreasing in the order OPC > SRPC > PFA > GGB S. Care is needed to minimise adverse effects occurring at transient pH val ues on the steady state data obtained in an acid neutralisation test. Howev er the indications are that differential acid neutralisation analysis may p rove to be very effective as an analytical technique. (C) 2000 Elsevier Sci ence Ltd. All rights reserved.