Mechanical behavior of construction and demolition waste-based alkali activated materials exposed to fire conditions

The mechanical behavior of materials based on the alkali activation of construction and demolition waste during and after their exposure to high temperatures was studied. The studied materials were based entirely on either, waste bricks or waste ceramic tiles, while a potassium hydroxide / sodium silicate solution was used as alkali activator. The compressive deformation of the alkali activated materials was tested during exposure to 850 - 1050 °C (on-fire testing) and the residual compressive strength was measured after exposure to 600 - 1050 °C for 2 h (post-fire testing), simulating the standard ISO 834 time-temperature curve. Microstructural changes and bulk properties were also assessed. The experimental results showed similar behavior of both materials in post-fire tests. Their compressive strength declined in between 600 and 800 °C and rose at 1050 °C, exceeding the initial value. Their density decreased 8 - 9% at 1050 °C, while their mass loss was 7 - 10% at this temperature. In the on-fire tests, the waste ceramic tile-based material presented plastic strain without any obvious macro-fracture at all the temperatures tested, while the waste brick-based material retained its elasticity and behaved as ceramic material up to 1000 °C with obvious macro-fractures. According to the experimental results, both alkali activated materials have the potential to be used as fire-resistant building materials. [Display omitted] •The alkali activated CDWs can be used as fire-resistant building materials.•Elastic behaviour of the brick waste-based alkali activated materials under load, up to 950 °C.•Pseudo-plastic strain of the ceramic tile waste -based alkali activated materials under load, at 850 °C and above.•Recovery of mechanical strength after cooling of the CDW-based alkali activated materials exposed to fire.•Microstructural transformations of the alkali activated materials at elevated temperatures affected the mechanical strength.