Effects of lignosulfonate on synthesis products of the pozzolanic reaction

Soil organic matters may inhibit the pozzolanic reaction, and thus influence the strength development of soil-employed construction materials. To understand their interaction, the effect of lignosulfonate, here used as model soil organic matter, on the pozzolanic reaction was investigated through batch experiments. Lignosulfonate inhibited the pozzolanic reaction, suppressing calcium silicate hydrate (C-S-H) formation. The suppression did not take place in a continuous way with the addition of lignosulfonate but was triggered at a certain dosage of lignosulfonate. We propose that the inhibition was primarily due to formation of Si-(Ca)-lignosulfonate complex. Such interaction may illustrate the inhibition of the pozzolanic reaction by organic matters in soils at alkaline activation. Below the threshold, lignosulfonate allowed C-S-H formation though modified its structure, which also suggested the possibility of soil organic matters to influence the strength development of construction materials in coexistence of C-S-H formation.