Measuring the membrane potential across cement-based materials

Cement-based materials tend to self-establish an electric field when expose d to an ionic concentration gradient. This is of importance in several area s of cement technology particularly where the prediction of ion transport i s required, such as in service life prediction of concrete structures and c ement-based solidification of hazardous waste. Measurement of the membrane potential across a specimen is the most direct method of quantifying the fi eld. The outcome of research directed at developing a sound method of measu ring membrane potentials is reported. Theory important to measure and inter pret membrane potentials is presented. The main variables involved in measu ring membrane potential are then considered, including specimen configurati on, electrolytes and reference electrodes. The greatest obstacle to accurat e membrane potential determination is the presence of junction potentials i n the test set up. Methods of minimizing and estimating junction potentials are presented. An example is presented involving measuring the potential a cross 10-mm-thick OPC mortar specimens housed between 0.5 M NaCl and simula ted pore solutions, using calomel electrodes and KNO3 salt bridges. The tot al junction potential involved was calculated to be around 2.2 mV. The corr ected membrane potential started at around -23 mV on first exposure, increa sing to a value of around +30 mV by 38 days.