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• Durability of porous perlite geopolymer was investigated in hot and humid environment. • The simulation of extremity of environment temperature and humidity on samples was conducted. • The durability effects of porous perlite geopolymer was analyzed. • The improvement of durability of porous perlite geopolymer was proposed. Porous geopolymers can be potentially applied in building thermal insulation. In this work, we investigated the durability of porous perlite geopolymer by long-term aging experiments under high temperature (50 ℃) and relative humidity (98%). Samples were characterized by digital photo analyses, scanning electron microscope (SEM), X-Ray Fluorescence Spectroscopy (XRF), X-Ray Diffractometer (XRD), Fourier Transform Infrared Spectrum (FT-IR), Solid-State Nuclear Magnetic Resonance (SS NMR), compressive strength measurements and thermal conductivity analyses. Results show that Na+ has great influence on the stability of porous perlite geopolymer. The hydrated Na+ in the pore reacts with CO 2 to form Na 2 CO 3 ·H 2 O, and part of Na+ enters and breaks geopolymer gel network, resulting in the deterioration of physical properties. When soaked in HCl or CaCl 2 solution, the geopolymerization is improved; at the same time, Na+ in the pore reacts with Cl– to form NaCl, and Ca2+ reacts with Cl– and OH– to form CaClOH, which jointly prevents Na+ from entering and breaking gel network and results in the improvement of durability of porous perlite geopolymer. Aging process promotes further polymerization in porous perlite geopolymer, which might also contribute to physical property variations of porous perlite geopolymer. This paper not only clarifies the mechanism of performance variation of porous perlite geopolymer in hot and humid environment, but also offers guidelines for the design and durability research of other porous geopolymers. [ABSTRACT FROM AUTHOR]

• A bifunctional hierarchical porous geopolymer with kaolinite was prepared. • Great thermal insulation and sound insulation performances. • The density is 0.086 g·cm−3 and compressive strength is high (0.27 MPa). • The pore diameter can be adjusted from 0.20 to 2.48 mm. Thermal and sound insulation materials are crucial for reducing the energy consumption and noise pollution of building, but these two types of materials are generally developed independently. Here, a new type of bifunctional hierarchical porous geopolymer which can effectively reduce heat transfer and noise sound is proposed and it is synthesized with inexpensive kaolinite as main raw material through an energy-saving method. The optimal porous geopolymer products show high porosity (93.80%) and extremely low density (0.086 g·cm−3) but relatively high compressive strength (0.27 MPa). More importantly, they have low thermal conductivity (0.040 W·m−1·K−1) but high sound absorption coefficient (0.539 at 5000 Hz; 0.809 at 500 Hz with gap of 50 mm) and sound reduction index (38.6 dB at 2000 Hz). Therefore, this hierarchical porous geopolymer can be potentially used as a new type of bifunctional building material to reduce the energy consumption and noise pollution of building at the same time. [ABSTRACT FROM AUTHOR]