Sorption and diffusion studies with low molecular weight organic compounds in cementitious systems

Abstract

The uptake of methanol, ethanol, formaldehyde, acetaldehyde, formic acid and acetic acid by cement paste was determined in hydrating cement after 1 h, 28 d and 390 d hydration. The sorption values determined for formate and acetate were critically assessed by investigating through- and out-diffusion of these compounds in fully hydrated cement paste and their uptake by individual cement phases. Diffusion studies included inverse modelling of four data sets for each compound and an uncertainty analysis based on a Latin hypercube sampling procedure. Solid–liquid distribution ratios determined from the hydration experiments are on the order of 10−4 m3 kg−1 in the case of alcohols and aldehydes indicating non-specific (very weak) bonding onto the surface of the cement phases, e.g. through hydrogen bonding. Hydration and diffusion studies reveal slightly higher distribution ratios and reversible uptake by cement paste and cement phases in the case of acetate indicating specific adsorption (electrostatic interaction) onto partially positively charged surface sites of the cement phases. Selective binding of a small fraction of formate is evidenced from both sorption and out-diffusion experiments suggesting the presence of sorption sites capable of strongly bonding the anion, presumably by SO42−/HCOO− replacement in the ettringite structure.