Inexpensive intumescent alkali-activated natural pozzolan pastes

Perlite, a natural pozzolan, was activated with NaOH to prepare alkali-activated (AA) intumescent pastes. After curing at 100 °C for 3-24 h, the solidified pastes had medium strengths, up to 40 MPa, and low densities, ∼1500-2000 kg/m3, compared to Portland cement pastes. Upon heating, volume expansion in the 200-600 °C range resulted in a porous solid. Expansion occurs due to a loss of silanol condensation water, as vapor. Chemical composition of the pozzolan, activator content, and heat-treatment temperature influence the size and amount of pores formed. Mechanical, physical, and microscopic investigations were made. Volume increases up to 225% were measured. Densities decreased to as low as ∼450 kg/m3 after heat treatment and cooling. Strengths of porous products were in the 3-7 MPa range. Such materials able to intumesce over specific temperature ranges could be useful in applications where absorption of thermal energy is necessary, such as passive fire protection.