Effect of potassium humate as humic substances from river sediments on the rheology, the hydration and the strength development of a cement paste

Abstract

Dredged river sediments may contain various types of organic matter that can affect the properties of a cement matrix, with the most representative part of such organic matter consisting of humic substances (HS). This work seeks to investigate the effects of humic substances on the rheology, the hydration and the strength development of a cement paste with different curing times, ranging from 1 to 90 days. Results show that adding organic matter to the cement paste offers greater workability by decreasing the yield stress. This addition also serves to retard the hydration of cement particles. Setting times increase to beyond one week when raising the amount of humic substances in the mixture, while the released heat ultimately reaches values comparable to those of the reference cement paste. Therefore, the addition of organic matter negatively affects strength development of the paste, especially at an early age; no resistance at 1-day has been noticed for HS content greater than 1%. Nevertheless, there was no significant reduction in the compressive strength up to 20% for HS content less than 1% at 90-day. In parallel, a study on pastes containing calcium lignosulfonate (water reducer) is carried out and the same effects are observed.