Stability of superplasticizer and shrinkage-reducing admixtures in high basic media

The present study explores the stability of different superplasticizer (polycarboxylate, vinyl copolymers, melamine and naphthalene derivatives) and shrinkage-reducing (polyproplyene glycol derivatives) admixtures in water and several alkaline media: NaOH (pH = 11.7 and 13.6), Ca(OH)(2) (pH = 12.4) and waterglass (pH = 13.0) solutions. The pH of the solutions was measured at different times and the structural changes taking place in the admixtures were studied using FTIR, FT-Raman and UV-VIS techniques. All the admixtures, except the naphthalene and polypropylenglycol derivatives in the NaOH pH = 13.6 solution and the naphthalene derivative in waterglass (Na2O.nSiO(2).mH(2)O + NaOH), are unstable at pH > 13.0. The other admixtures all undergo structural changes in highly basic media that explain the loss of their fluidifying properties under these conditions.