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A density functional theory method was employed to conduct theoretical calculations on the pyrolysis reaction pathways of lignin monomer model compounds with an aldehyde or carboxyl group under the catalytic effect of alkali metal ions Na+ and K+, exploring their influence on the formation of the small molecular gaseous products CO and CO2. The results indicate that Na+ and K+ can easily bind with the oxygen-containing functional groups of the lignin monomer model compounds to form stable and low-energy complexes. Except for benzaldehyde and p-hydroxybenzaldehyde, Na+ and K+ can facilitate the decarbonylation reactions of other benzaldehyde-based and phenylacetaldehyde-based lignin monomer model compounds during the pyrolysis process, thereby enhancing the generation of CO. When the characteristic functional groups on the benzene rings of benzaldehyde-based and phenylacetaldehyde-based lignin monomer model compounds are the same, the phenylacetaldehyde-based ones are more prone to undergo decarbonylation than the benzaldehyde-based ones. Additionally, both Na+ and K+ can inhibit the decarboxylation reactions of benzoic acid-based and phenylacetic acid-based lignin monomer model compounds, thereby restraining the formation of CO2. When the characteristic functional groups on the benzene rings of benzoic acid-based and phenylacetic acid-based lignin monomer model compounds are the same, the phenylacetic acid-based ones are more difficult to undergo decarboxylation than the benzoic acid-based ones. [ABSTRACT FROM AUTHOR]

Foam concrete is a promising material in building and construction applications, providing such outstanding properties as high specific strength, excellent thermal insulation, and effective acoustic absorption in human-inhabited buildings. However, because the porosity and permeable water absorption properties of foam concrete are significantly higher, its durability is often not comparable to that of ordinary concrete, and so the durability of foam concrete requires significant attention during the life cycle of building applications. Durable materials can greatly reduce the environmental impact of waste from maintenance and replacement and the consumption of natural resources resulting from the production of repair and replacement materials. After hardening, the durability of foam concrete includes freeze-thaw cycle resistance, elevated temperature resistance, carbonation resistance, efflorescence resistance, sulfate resistance, chloride resistance, alkali-silica reaction, and so on. This paper reviews articles on the durability of ordinary Portland cement (OPC) foam concrete, geopolymer foam concrete (GFC), magnesium phosphate cement (MPC) foam concrete, sulphoaluminate cement (SAC) foam concrete, and limestone calcined clay cement (LC3) foam concrete and compares their durability to provide a reference for the life cycle design and service life estimation of foam concrete members. [ABSTRACT FROM AUTHOR]