Joint project "Low energy concrete"

Globally, the building sector consumes around 40% of the energy and usually the largest share is represented by operation. Continuous improvements of energy-efficiency in building have reduced the share of operation energy to increase the relevance of embodied energy in materials. The 2000W Society standard for sustainable buildings considers that new buildings allocate 70% of their energy for the building construction and 30% for its operation. In Switzerland, concrete is still the most widely used material in construction and a reduction of its grey energy and carbon emissions is an urgent task that needs to be tackled to facilitate the energy turnaround.

The joint project aimed to reduce the impact from the use of construction materials, and in particular from concrete structures. Further reductions of cement emissions are possible through the increase of the clinker substitution; however, this is limited due to the loss of mechanical strength and high risk of rebar corrosion. As a consequence, the projects aimed at reducing clinker content at material level without losing the early strength, while at the same time developing structural solutions that replace steel with non-ferrous materials.

At material level, a new ternary-blend cement has been developed with a clinker reduction of up to 65% without losing the early strength capacity. At structural level, new concrete solutions with non-metallic reinforcement where tested and developed, in order to avoid durability issues. Results showed that high cement substitution with supplementary cementitious materials (SCM) is able to cut the emission up to 50%, while at structural level 80% of carbon saving is possible due to the optimisation of material and structural hybridisation.

Relevance for research

The project achieved valuable results from a research prospective. In particular, it demonstrated that a high substitution of clinker in concrete is possible without losing early strength. The low pH of the new concrete mixture does not necessarily affect the carbonation-induced corrosion of traditional steel-reinforced structures. High resistance to corrosion under regular environmental conditions was measured, while a higher risk is expected in very humid conditions. New radically innovative concrete structures are able to reduce both embodied energy and carbon emissions over the whole life cycle of a building and future dematerialisation can lead to additional carbon emission saving.

Relevance for practice

The targeted concrete technologies lead to significant energy saving for the energy turnaround if the solutions are implemented. The influence of stakeholders will play a fundamental role for a fast transition. At material level, the low clinker cement can be produced by using the same infrastructures and facilities already adopted by cement manufacturing companies for conventional cement. Thus, no change of cement infrastructure is required. Additional supporting data for designers and contractors can be provided by ongoing durability tests on real-case steel reinforced concrete structures. This data will be crucial in demonstrating the safety of the new concrete structures and contribute to removing the barriers that typically exist in a sector as conservative as construction.

Concrete Solutions

The joint project consists of five research projects

Formulation, use and durability of concrete with low clinker cements

• Prof. Robert J. Flatt, Institut für Baustoffe, ETH Zürich; Prof. Bernhard Elsener, Prof. Karen Scrivener, Dr. Marta Palacios

Next generation UHPFRC for a sustainable built environment

• Dr. Emmanuel Denarié, Laboratoire de maintenance, construction et sécurité des ouvrages, EPF Lausanne; Prof. Eugen Brühwiler, EPF Lausanne

Beech wood concrete hybrid structures

• Prof. Andrea Frangi, Institut für Baustatik und Konstruktion, ETH Zürich; Prof. Ingo Burgert

Low-clinker, high-performance concrete elements pre-stressed with carbon-fiber reinforced polymer reinforcement (LCHPC)

• Prof. Pietro Lura, Abteilung Analytische Chemie, EMPA Dübendorf; Dr. Giovanni Pietro Terrasi

Getting more out of Structures through Monitoring and Simulation

• Prof. Eleni Chatzi, Institut für Baustatik und Konstruktion, ETH Zürich; Prof. Eugen Brühwiler, EPF Lausanne