Retardation of Portland Cement Hydration with Photosynthetic Algal Biomass

In this work, the effects of raw algal biomass on the hydration kinetics of portland cement are reported. Specifically, direct addition of 0.3%, 0.5%, 1.0%, and 3.0% photosynthetic Chlorella algal biomass to cement paste substantially delayed cement hydration, as indicated by 16.5%, 29.4%, 82.4%, and 812% delays in the main peak of heat evolution measured by isothermal calorimetry. Retardation was confirmed via FTIR to be mechanistically caused by the existence of -COOH and -OH functional groups in raw algae. We substantiated the observation that elimination of -COOH and -OH functional groups in the algae through heat treatment coincided with the disappearance in the retardation effect, while enhancement of these functional groups through H2O2 treatment induced further retardation. In addition, the effects of untreated and treated algae on the morphology, mineralogy, and compressive strength of cement pastes containing 0.5% Chlorella were found to be negligible. An addition of 0.5% algal biomass is estimated to cost approximately USD $1.6-2.6/m(3) of concrete, suggesting that raw algae could be used as a renewable, cost-competitive, CO2-storing set-retarding admixture for portland cement-based materials.

Automated summary

The study found that adding different proportions of raw algal biomass significantly delays cement hydration, with the retardation effect further influenced by the manipulation of functional groups in the algae through treatment. The effects of algae on the morphology, mineralogy, and compressive strength of cement pastes can be considered negligible. Overall, raw algae could serve as a renewable, cost-competitive, CO2-storing set-retarding admixture for cement-based materials.