Pore solution measurements

Paste samples were cast with a water to binder ratio of 0.46 or 0.6; the higher w/b samples were prepared to allow the collection of pore solution from paste samples after several months. The paste and concrete samples were cast in polypropylene containers with the volume of 200 ml (approximate diameter 55 mm and height 80 mm) after mixing and stored at different temperatures (20 and 40 °C). The pore solutions of the paste and concrete samples were extracted using a compression-testing machine at room temperature. The force used was variable for different paste samples from 300 to 900 kN, and from 1400 to 2200 kN for concrete samples.

The extracted pore solution was immediately filtered after extraction using a 0.2 µm nylon microfilter. In order to measure pH, almost 2 ml of the solution was put in a small plastic container and voltage and temperature were measured after 2 min of equilibration time with a pH electrode (BlueLine 14 pH, SI Analytics)) connected to a Lab 850 pH meter and at the laboratory temperature of ≈ 25 °C. The mV readings were calibrated against potassium hydroxide solutions as detailed in [30, 31]. The pH values are reported at laboratory temperature (25 °C). At high Na or Li concentrations, too low pH readings result due to the so-called alkali error [31], which was corrected based on reference measurements carried out with KOH, NaOH, and LiOH solutions: The pH value was corrected by + 0.2 for 200 mmol/L and by + 0.3 for 300 mol/L of Na and by + 0.35 for 200 mmol/L Li and by + 0.7 for 400 mol/L of Li, comparable to the differences reported in [31].

The remaining solution was immediately diluted 3 or 10 times using ultra-pure water, and stored in the fridge until measuring using Inductively Coupled Plasma Optical Emission Spectrometry (ICP–OES (Shimadzu ICPE–9000)), or Ion Chromatography (IC, Thermo Scientific Intergrion HPIC or Dionex DP ICS-3000 ion chromatograph).