Reactions involved in carbonation hardening of Portland cement: effect of curing temperature

Abstract

CO₂ curing of fresh concrete is one of the solutions allowing direct carbon sequestration within the construction industry. Additionally, it enhances the early mechanical performance when comparing to traditional hydration curing. Temperature of carbonation curing has pronounced impact on both reactions involved in hardening of Portland cement: carbonation and hydration. Both reactions are accelerated with rising temperature, while the formed products and resulting microstructure are altered. Higher curing temperature promotes the precipitation of silica gel and C-S-H phase with reduced Ca/Si ratio. Furthermore, alumina and sulfate distributions among the reaction products are different. Temperature of carbonation curing has a distinct impact on the cement paste hydration after carbonation curing. The high curing temperature results in a densification of the matrix which limits further reaction progress, compared to the samples cured at lower temperatures. During the post hydration, calcium deficient system changes into C-S-H phase with higher Ca/Si and eventually portlandite.

Keywords:

• Reaction mechanisms
• kinetics
• phase assemblage
• carbonation curing
• CO₂ sequestration
• calcium carbonate

Acknowledgments

The support of the ANC laboratory regarding the experimental work is greatly appreciated. The fruitful discussions with Tim Schade, Jannes Koenig, Jan Skocek, and Martina Dietermann are acknowledged.

Authors’ contributions

Maciej Zajac: Conceptualization, supervision, project administration, methodology, investigation, formal analysis, visualization, writing – original draft, writing – review and editing. Harald Hilbig: Supervision, investigation, formal analysis, visualization, writing – original draft. Frank Bullerjahn: Investigation. Mohsen Ben Haha: Supervision, writing – original draft.

Additional information

Funding

This work has been carried out within the project “K4 – Kohlendioxidreduktion durch kalkarme Klinker und Karbonatisierungshärtung” (01LJ2007). The project is funded by the German Federal Ministry of Education and Research (BMBF).