Accelerated Ageing of Blast Furnace Cement-Dolomite Mortars: Phase Changes, Microstructural Evolution, and Mechanical...

Area of Science:

• Materials Science
• Construction Chemistry
• Geochemistry

Background:

• Blast furnace cement (CEM-III/B) utilizes slag, but its hydration and long-term performance in alkaline environments require further understanding.
• Dolomite's role in cementitious materials, particularly in slag-based cements under accelerated ageing, is not fully elucidated.

Purpose of the Study:

• To investigate the influence of natural dolomite on the hydration products and microstructural evolution of blast furnace cement-dolomite mortars.
• To determine the effect of dolomite on slag hydration kinetics and the resulting mechanical strength development under accelerated alkaline ageing conditions.

Main Methods:

• Mortars prepared with CEM-III/B (75% slag) and dolomite aged in 1 M NaOH at 60 °C for up to 24 months.
• Hydration products and microstructure analyzed using X-ray Diffraction (XRD), Thermogravimetric Analysis (TGA), and Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM-EDS).

Main Results:

• Dolomite presence enhanced slag hydration by promoting Ca and Si dissolution, attributed to released carbonates during dedolomitisation.
• A multi-rim structure formed around slag particles, featuring hydrotalcite-like phases and C-S(A)-H gel, with monocarbonate observed at the slag-paste interface.
• Increased mechanical strength correlated with higher hydration product content and microstructural densification via calcium carbonate formation and C-S(A)-H gel carbonation.

Conclusions:

• Dolomite acts as a chemically active component, not inert filler, in blast furnace cement mortars under alkaline ageing.
• Dolomite significantly influences slag hydration kinetics and the composition of hydration products, leading to improved long-term performance.
• The study provides insights into the synergistic effects of slag and dolomite in cementitious systems for enhanced durability.