Scientists Create First Fire Proof Self-Compacting Concrete

Self-compacting concrete, which does not need to be vibrated to become fully compacted, has many advantages on a job site, such as lower overall costs, faster construction times, no need for a concrete vibrator, and thinner concrete sections.  One of the major disadvantages of this type of concrete, however, is that it’s notoriously poor in regards to fire resistance.  Traditional concrete solves the fire resistance problem by adding polypropylene (PP) fiber, which allow the concrete structure to stay intact when it comes in contact with fire.

When PP is added to self-compacting concrete in the same ratio, though, it prohibits the concrete from self-compacting, thus eliminating any benefits.  Now, researchers from EMPA’s Concrete/Construction Chemistry and Mechanical Systems Engineering Laboratories, have figured out how to lower the amount of PP by pre-stressing a series of thin-walled concrete slabs with cables made out of carbon fiber reinforced polymer.  The self-compacting concrete was also mixed with a low amount of PP and a small quantity of super absorbing polymer (SAP) was added in several of the test slabs, as well.

Photo credit: Luke Bisby, The University of Edinburgh

After exposing all of the test slabs to heat of roughly 1,852 °F (1,000 °C), the researchers determined that the slabs with SAP added only resulted in minor cracking, whereas the other slabs without the SAP added chipped and flaked, also known as spalling, under the intense heat.

So why did the slabs with SAP added perform so well? In typical concrete, PP will burn when exposed to fires and, in turn, create tiny voids in the concrete, which provides space for water vapors to escape, lowering the internal pressure of the concrete.  Since self-compacting concrete cannot perform with the same amount of PP, the SAP mimicked the same properties.  During manufacturing, SAP is saturated with water and slowly shrinks after placed in concrete, creating tiny voids in the concrete.