Julson Tchio: Advanced Surface Modification and Characterisation of Low-CO₂ Steel Slag Cement

Advanced Surface Modification and Characterisation of Low-CO₂ Steel Slag Cement

By Julson Tchio

Overview

From Industrial Waste to Tomorrow’s Buildings
Transforming Steel Slag into Sustainable Construction Materials

Every day, massive steel plants across Finland—SSAB, Outokumpu, and others—produce the steel that becomes our cars, buildings, and bridges. But they also create mountains of slag, a rocky by-product that looks almost volcanic after it cools. For decades, this material has been treated as waste, while Finland continues to import thousands of tons of cement annually, along with its embedded emissions.

This research addresses a clear paradox: that “waste” slag could replace what is currently being imported.

Why This Matters

Cement production is responsible for 8% of global CO₂ emissions—more than all trucks worldwide. The process has remained largely unchanged for 200 years: heating limestone to 1,450°C in energy-intensive kilns, followed by additional emissions from the chemical reaction itself.

As global infrastructure expands, the environmental cost increases. The construction industry must transform—and the materials to do so already exist.

Research Focus

Steel slag contains the same key elements as cement, such as calcium, silicon, and aluminum. The energy-intensive transformation has already taken place during steel production.

This research focuses on identifying how to activate slag so it can function as a binding material—creating strength and durability comparable to cement, but with significantly lower environmental impact.

The work is conducted between the University of Oulu’s Fibre and Particle Engineering research unit and the University of Sheffield’s SMASH group, focusing on transforming industrial by-products into high-performance construction materials.

Scientific Challenge

Hardened cement is a highly complex material. At the microscopic level, it consists of evolving networks of crystals, gels, pores, and interfaces.

Replacing Portland cement with steel slag introduces entirely new variables: different chemistry, crystal structures, reaction rates, and long-term performance characteristics. This research aims to understand, map, measure, predict, and optimize these factors.

Using X-ray tomography at Sheffield, 3D models of cement internal structure are created to study pore networks, crack formation, and structural evolution over time. Different slag types—such as Blast Furnace Slag and Electric Arc Furnace slag—are tested with various activation methods and compared to Portland cement across multiple performance indicators, including strength, durability, and environmental resistance.

Impact

The research focuses on alkali-activated materials, supplementary cementitious materials (SCMs), and geopolymers—alternative binders that can significantly reduce the carbon footprint of construction.

Key findings show that certain slag formulations can achieve comparable or superior strength to Portland cement, demonstrate promising long-term durability, and reduce carbon emissions by 50–80% depending on formulation.

Every ton of Portland cement replaced eliminates approximately 0.9 tons of CO₂ emissions. At scale, replacing even 30% of global cement could reduce total global emissions by 2–3%.

Support & Collaboration

Research of this scale requires significant resources. Advanced methods such as X-ray tomography, chemical analysis, and international collaboration are costly but essential.

The Walter Åström Foundation’s travel grant enabled hands-on collaboration with leading experts at the University of Sheffield, access to world-class equipment, participation in international conferences, and the development of long-term research partnerships.

Additional support from the EU Marie Skłodowska-Curie Action I4WORLD program has enabled sustained and ambitious research beyond short-term experimental work.

The research is supervised by Prof. Juho Yliniemi (University of Oulu), Prof. Brant Walkley (University of Sheffield), and Dr. Elijah Adesanya (University of Oulu), whose guidance has been instrumental in shaping the work.

Outlook

This research reflects a broader shift toward circular economy thinking: transforming industrial by-products into valuable materials.

Finland is uniquely positioned to lead this transition, with a strong steel industry, advanced research infrastructure, and a commitment to sustainability.

The vision is clear:
The concrete of tomorrow can be built from yesterday’s waste—durable, scalable, and significantly more sustainable.