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Lignopolymer Superplasticizers for Low-CO 2 Cements

2017; American Chemical Society; Volume: 5; Issue: 5 Linguagem: Inglês

10.1021/acssuschemeng.7b00021

2168-0485

Chetali Gupta, Elizabeth Nadelman, Newell R. Washburn, Kimberly E. Kurtis,

Recycling and utilization of industrial and municipal waste in materials production

Grafting hydrophilic polyacrylamide from a kraft lignin core results in a lignopolymer that effectively plasticizes portland cement paste. Here, the potential of this sustainably sourced lignopolymer is examined for improving the workability of portland cement blended with two natural, finely divided mineral materials (kaolin clay and clinoptilolite zeolite), which can be potentially used in combination with portland cement as a means to reduce the cement clinker content and the concomitant embodied energy and greenhouse gas emissions in concrete. Both mineral materials are known to affect cement hydration reactions but can significantly reduce workability when blended with portland cement, presenting a challenge for their practical large scale use.1,2 The plastic behavior of mineral-cement combinations dosed with polyacrylamide-grafted kraft lignin was compared to the behavior of those with a lignosulfonate developed for plasticizing portland cement and a commercial polycarboxylate ether (PCE). Compared to the other admixtures, the lignopolymer was found to adsorb strongly to both kaolin and clinoptilolite and resulted in the lowest yield stresses in pastes containing 25% mineral material and 75% Type I/II portland cement at both high (5 mg/mL, 0.25 wt %) and low (0.5 mg/mL, 0.025 wt %) admixture content, but no significant retardation was observed in calorimetry measurements of hydration kinetics. In contrast, the PCE had a low affinity for both mineral admixtures at higher concentrations compared to that of both lignin superplasticizers, and the resulting tests of slump spread and viscosity were similar for these two minerals. Lignosulfonates had affinity for the mineral phases similar to that of the other superplasticizers but were ineffective at improving workability, pointing to the need for steric interactions in plasticizing mineral materials used in combination with cement. These results indicate that lignopolymers could be an effective superplasticizer for a broad range of high surface area minerals to be used in combination with portland cement.