TRANSPORTATION OF IONS THROUGH CEMENT-BASED MATERIALS .3. EXPERIMENTAL-EVIDENCE FOR THE BASIC EQUATIONS AND SOME IMPORTANT DEDUCTIONS

In parts 1 and 2 of this series it has been suggested that ion transport, through cement based materials, can properly be described only by using a combination of Nernst, Nernst-Planck and the electrical double-layer diffusion processes. In this part experimental evidence, from diffusivity measurements, for the above statement is presented. The results show that the diffusivity of Cl- is higher when CaCl2 is the diffusant than when an alkali chloride is the diffusant; it also decreases with increasing concentration of diffusant solutions. The diffusivity of R+ ions, on the other hand, increase with the concentration of alkali halide solutions. The diffusivity of Cl- is higher, by an order of magnitude, than those of R+ ions. Ca2+ co-diffuse with R+. The diffusant solutions themselves becomes highly alkaline. It has been shown that the above results are in conformity with the opening statement. The present approach also allows for an estimation of bound Cl- from diffusion data itself. It has been shown that the movements of positive and negative ions are coupled. This coupled diffusion explains the previously reported high activation energy of Cl- diffusion. It is emphasized that an expressed pore solution has a different composition from that actually in contact with the cement hydration products.