Alkali-O₂ oxidized lignin: A bio-based concrete plasticizer

Commercial wheat straw soda lignin was used to develop an alkali-O₂ oxidation method to produce a ready-to-use solution for concrete plasticizing (cement dispersing). Lignin characterization was done directly from the solution. Depending on conditions, oxidation primarily induced either condensation or degradation of lignin. Thus, both the negative charge and the molar mass of the lignin were controlled by the oxidation parameters, and especially by pH. The oxidized lignins were evaluated for their plasticizing performance in cement pastes, mortar, and concrete. Also, their effect on cement hydration was followed and several other properties of fresh andmatured concrete were tested. A commercial lignosulfonate and petroleum-based superplasticizers were used as reference products.The results indicated that alkali-O₂ oxidation at moderately high lignin dry solids is a promising methodto produce a novel bio-based concrete plasticizer. The oxidized lignins were superior to the lignosulfonate and showed good performance in comparison to the superplasticizers.