Mike Stanzel & Oliver Sohn, Chryso North America, present a multilayered approach to maximising blended cement performance for use in concrete.
The landscape of cement manufacturing is evolving, driven by the need for more sustainable and lower embodied carbon construction materials. The introduction of blended cements, incorporating supplementary cementitious materials (SCMs), including finely ground limestone, has presented challenges for many cement producers. These challenges include reduced strength, leading to increased Blaine specific surface area (BSSA) and lower production rates, and subsequent field performance issues, such as higher water demand, reduced bleeding rates, plastic shrinkage cracking, and changes in set-times. These factors have led to some reluctance in certain markets to fully adopt these new materials.
While advanced grinding additives have helped regain some of the lost performance and production capacity, a more comprehensive approach is necessary to fully recover the desired performance and production levels of traditional ordinary portland cement (OPC). One must address the four critical levers essential for optimising blended cements to match traditional OPC expectations: proper clinker formation, mill optimisation, effective additive selection, and optimising quality targets.
By addressing all four key areas, cement producers can overcome the challenges associated with blended cements and achieve the performance and sustainability goals required in today's construction environment. Only by satisfying all four levers can the desired performance be achieved and sustained, ensuring that blended cements can meet modern needs without compromising on quality or efficiency.
Clinker formation
Clinker is the primary intermediate product in cement manufacturing, and its quality directly impacts the potential performance on the final cement. Producing high-quality clinker consistently is a significant step to reducing emissions through supplementary material use, while meeting construction demands in the field. This involves careful control of:
- Chemical composition: particularly alite content, aluminate content, liquid phase to ensure good combinability, and a proper alkali-sulfur balance to avoid inhibiting C3S formation and cycling of the system.
- Raw milling parameters: particularly kiln feed uniformity and sufficient target fineness to avoid free-lime and belite clustering.
- Burning and cooling conditions: ensuring oxidising conditions, proper burner alignment, rapid heating and cooling, and proper clinker density.
All of this not only impacts cement performance, but also clinker grindability, which is key to optimising combined particle size distributions of inter-ground blended cements.
While grinding additives can help address quality and process issues, they are most effective when the clinker quality is high to begin with. Quite simply, the better the clinker, the better the synergy with additives, the better the cement, and the happier the contractor out in the field.
Mill optimisation
Mill maintenance and optimisation is a critical area that often does not receive enough attention and budget allotment. Over the past two years, Chryso has conducted in excess of 350 mill audits globally, and identified several recurring issues. While chemical additives have proven to work even when a process is sub-optimal, minor operational adjustments and proper maintenance can result in significant improvements to both cement quality and mill output.
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