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=l2.4) and waterglass (pH=13.0) solutions. The pH of the solutions was measured at different limes 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=l3.6 solution and the naphthalene derivative in waterglass (NaO2-nSiO2-mH2O + 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.
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Palacios et al. (2004) studied this question.
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