Speaker
Description
Ternary calcium sulfoaluminate (CSA)–Portland limestone cement (PLC)–calcium sulfate binders are increasingly used for tunnel repair due to their controlled setting behaviour and rapid strength development. In these systems, calcium sulfate availability and dissolution rate govern ettringite formation and hydration kinetics, directly influencing workability, setting time and early mechanical performance.
This work investigates the role of calcium sulfate in terms of origin, mineralogy and fineness in the development of a PLC–CSA binder within an industrial framework. A low-CO₂ Portland cement was first selected to balance performance and environmental impact. Eight different calcium sulfate sources were evaluated, including gypsum and anhydrite of natural, synthetic and recycled origin.
The materials were processed through both simple blending and industrial co-grinding to assess the effect of production route and fineness on system reactivity. The resulting binders were tested in standard mortar to evaluate workability, setting time and compressive strength development. Clear differences were observed depending on sulfate type and processing method, particularly in terms of setting window and early strength evolution.
Based on the screening phase, the most suitable sulfate source was selected and produced through industrial co-grinding. The optimized binder was subsequently validated in concrete mixtures designed for tunnel applications. Mix design parameters, including the use of chemical admixtures and low water-to-binder ratios, were adjusted to meet practical requirements. Fresh properties, setting behaviour and strength development were assessed under representative application conditions.
The results confirm that appropriate selection of calcium sulfate type and control of fineness enable reliable regulation of setting and mechanical performance at both mortar and concrete scale, supporting the development of industrial repair binders.
Affiliations
Built - Buzzi Innovation Laboratory and Technology, Via Riccardo Restano 3, Vercelli, Italy, 13100, valentino.merlo@buzzi.com
| Keywords | Cement binders, calcium sulfoaluminate cement, Concrete, Workabilty, Co-grinding |
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