Hydration of water- and alkali-activated white Portland cement pastes and blends with low-calcium pulverized fuel ash

Pastes of white Portland cement (wPc) and wPc-pulverized fuel ash (pfa) blends were studied up to 13 years. The reaction of wPc with water was initially retarded in the presence of pfa particles but accelerated at intermediate ages. Reaction with KOH solution was rapid with or without pfa. A universal compositional relationship exists for the C-A-S-H in blends of Pc with aluminosilicate-rich SCMs. The average length of aluminosilicate anions increased with age and increasing Al/Ca and Si/Ca; greater lengthening in the blends was due to additional Al3+ at bridging sites. The morphology of outer product C-A-S-H was always foil-like with KOH solution, regardless of chemical composition, but with water it had fibrillar morphology at high Ca/(Si+Al) ratios and foil-like morphology started to appear at Ca/(Si+Al) ≈1.2-1.3, which from the literature appears to coincide with changes in the pore solution. Foil-like morphology cannot be associated with entirely T-based structure

Using X-ray fluorescence to assess the chemical composition and resistivity of simulated cementitious pore solutions

Ionic transport in concrete can be described using the formation factor, which is the ratio of the resistivity of the concrete and the pore solution resistivity. The pore solution resistivity may be assumed, directly measured, or computed from the pore solution composition. This paper describes an experimental investigation aimed at determining the feasibility of using X-ray fluorescence (XRF) to obtain the alkali concentrations of the pore solution which enable the calculation of pore solution resistivity. In order to do this, simulated pore solutions containing known amounts of sodium and potassium were prepared and analyzed using XRF. XRF was performed on two sample types: (1) the simulated solutions and (2) beads where the water from the solution is evaporated and the remaining material is fused using a fluxing agent. The compositions obtained experimentally from XRF are compared to known compositions to demonstrate the accuracy of the technique. In addition, the measured simulated pore solution resistivity was compared to the simulated pore solution resistivity calculated from XRF measurements. The results indicate that the composition had an average error of 0.50% while the estimated simulated pore solution resistivity had an average error of 10.95%. The results of this study indicate that XRF has the potential to be an alternative to the time consuming methods currently used to measure the composition of the pore solution