5. Conclusions
A series of alkyl-ethylene oxide polymers (AEOPs) synthesized with controlled variations of their main structural elements was investigated by a wide range of techniques to determine their effect on the drying behavior of well-hydrated white cement pastes. The following conclusions have been reached:
1) AEOPs can subtly change the shape of water vapor sorption isotherms, displacing the kink in the desorption branch from around 35% RH (for DEG) and 40% RH (for the plain paste) up to about 75% RH in the extreme case. Displacement of the kink to higher RH roughly correlates with a greater degree of shrinkage reduction, with an optimum at about 70% RH. This mechanism might be explained by the increase of critical vapor pressure due to the presence of better hydrophilic-lipophilic balance AEOPs in mesopores connecting to necking pores causing cavitation. This apparent optimal kink position corresponds with the use of the two most effective shrinkage-reducing AEOP molecules, C4-EO-2 and C8-EO-20, both of which gave only about half the drying shrinkage of the control paste. These molecules apparently have the best balance between the hydrophobic alkyl group and the hydrophilic poly-EO chain.
