Effect of citric acid-modified chitosan on the hydration and microstructure of Portland cement paste

Abstract

In this study, citric acid-modified chitosan (CAMC) is prepared by an acylation reaction to regulate the exothermic process occurring in cement hydration. The thermodynamic process of cement hydration is characterized by isothermal calorimetry. The effects of various CAMC contents of 0%, 0.2%, 0.4%, and 0.6% on the hydration process were systematically studied by X-ray diffraction (XRD), inductively coupled plasma emission spectroscopy (ICP–OES), and proton nuclear magnetic resonance (¹H-NMR). The results show that the adsorption effect delays the dissolution of alite (C₃S). The content of CAMC is shown to have a significant effect on the formation time and amount of ettringite (AFt), and the competitive adsorption relationship increases the concentration of Ca²⁺. The increases in Ca²⁺ and SO₄^2- concentrations resulted in an increase in the AFt amount. With prolongation of the hydration, the capillary pores of the cement paste are transformed into gel pores, and the cement slurry exhibits a self-drying phenomenon.

Highlights

• Designed and prepared citric acid modified chitosan.

• Adsorption delays the dissolution of C ₃ S and the formation of hydrated products.

• Competitive adsorption increases calcium ion concentration.

• CAMC delays the formation of AFt and increases the amount of AFt formation.

Keywords:

• CAMC
• ion concentration
• competitive adsorption
• pore size
• hydration degree

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The authors greatly acknowledge the National Science Fund for Distinguished Young Scholars, China (51925903). General Program of National Natural Science Foundation of China (51878155). National Postdoctoral Program for Innovative Talents (BX2021065). China Railway Science and Technology Research and Development Program “Research on Key Technologies of Key Stations in Beijing-Tianjin-Hebei Region” (P2018G049).