Early age reaction of slag in composite cement: Impact of sulphates and calcite

Sam Adu-Amankwah*, Leon Black, Liu Xianfeng, Pengkun Hou, Maciej Zajac

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Ground granulated blast furnace slag (GGBS) is an important supplementary cementitious material (SCM) for producing low carbon and durable concrete. There are however questions around the early age reactivity of GGBS and the factors that influence this. To elucidate the fundamental mechanisms controlling the early age reactivity and particularly the influence of anionic species, simplified systems comprising GGBS and calcium hydroxide were examined in the presence of limestone, anhydrite, or both at 4:1 SCM-to-activator ratio. Limestone and GGBS were considered as SCMs, but calcium hydroxide and anhydrite were considered as activators. Multiple techniques, including isothermal calorimetry, thermogravimetry, X-ray diffraction, electron microscopy, mass balance calculation and mercury intrusion porosimetry were used to study hydration and microstructure. The results show that GGBS hydration commences immediately in the alkaline media provided by calcium hydroxide. Sulphates and limestone influence hydration through reactions with aluminates to form ettringite and carboaluminates, but prevalence of macro-capillary pores in sulphate containing binders sustains diffusion-controlled hydration. Consequently, optimization of the alumina to sulphate and carbonate ratios is essential for exploiting the pore solution and space filling effects in composite cements.
Original languageEnglish
Pages (from-to)100085
Early online date14 Sept 2023
Publication statusE-pub ahead of print - 14 Sept 2023


Dive into the research topics of 'Early age reaction of slag in composite cement: Impact of sulphates and calcite'. Together they form a unique fingerprint.

Cite this