Perlite, a natural pozzolan, was activated with NaOH to prepare alkali-activated (AA) intumescent pastes. After curing at 100 degrees C for 3-24 h, the solidified pastes had medium strengths, up to 40 MPa, and low densities, similar to 1500-2000 kg/m(3), compared to Portland cement pastes. Upon heating, volume expansion in the 200-600 degrees 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 similar to 450 kg/m(3) 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. (C) 2015 Elsevier Ltd. All rights reserved.