Summary
The point at which the rate of hydration of the alite phase in clinker, which is very slow in the beginning, starts to accelerate and the cement paste begins to turn solid can be determined with a copper-lead electrode. This point is clearly indicated by the distinct increase of potential difference when the surface of copper oxidizes to cuprous oxide as air penetrates to the capillary space. Air dissolved in the mixing water does not cause oxidation, nor does entrained air present under practical working conditions. Because of the total absence of the disturbing influence of the aggregate, this method of determining the setting time of mortar or concrete is more accurate than the commonly used mechanical methods and it also yields results which better correspond to the actual situation. The reaction vessel need not be of any specific shape, and therefore direct placement of the electrode, for instance, in a unit mould is possible. In principle, this method is also applicable to hydraulic bonding agents other than Portland cements.
