Researchers from Empa's Concrete/Construction Chemistry and Mechanical Systems Engineering Laboratories have found a way to make self-compacting high-performance concrete (SCHPC) fire resistant, so buildings made of it are safer, while keeping the proportion of polymer fibers low enough that the concrete remains self-compacting.

The Problem: When concrete is exposed to fire it chips and flakes – a process known as spalling. The phenomenon is caused when water trapped within the concrete element vaporizes due to the high temperature. As more water vapor is produced the pressure within the concrete structure increases. Chips split away from ceilings, walls, and supporting pillars, reducing their loadbearing capacity and increasing the risk of collapse in a burning building.

The Solution: Researchers manufactured a series of thin-walled concrete slabs which were pre-stressed with cables made of carbon fiber reinforced polymer. The concrete from which the slabs were made also contained 2kg of PP fiber per cubic meter of mixture. In some slabs the scientists also added a small quantity of super absorbing polymer (SAP), a synthetic material which is capable of absorbing many times its own weight in water. They then exposed the concrete slabs to fire, reaching temperatures of up to 1000°C. After 90 minutes it became clear that while the SAP-containing concrete slabs showed some minor cracking, spalling occurred only in the SAP-free slabs.

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