It is well known that under certain circumstances sodium chloride and calcium chloride can be found dissolved in the liquid phase of concrete. There have been a number of reports stating that these salts can produce reductions in concrete alkalinity. Furthermore it has been suggested that the magnitude of the ph reductions is sufficient to enhance the influence of chlorides, one of the primary agents causing corrosion of concrete reinforcement. In this report the influence of nacl, kcl and cacl2 additions on the ph of saturated ca(oh)2 solution, 0.04m koh and cement-water extracts has been investigated experimentally and the results compared with calculated ph changes based on ionic equilibria and the theory of more concentrated electrolyte solutions. It was concluded that even when the liquid phase of concrete contained high salt concentrations the maximum ph reduction arising from this effect was only 0.5 ph unit and generally ph decreases were substantially less than this. This level of ph reduction is not likely to have a significant influence on the effectiveness of concrete as a protective cover for the steel reinforcement. (Author/publisher)
Samenvatting