Abstract
Abstract In this study, the effect of SiO2/Al2O3 (S/A), Na2O/Al2O3 (N/A) and H2O/Na2O (H/N) molar ratios on bending and compressive strength of geopolymer were investigated. The geopolymerization mechanism was also analyzed from microstructure difference by FTIR. The experimental results showed that compressive strength and bending strength of geopolymer has an opposite reaction under different critical molar ratios. The increase of S/A molar ratio and the decrease of N/A and H/N molar ratios have resulted in an increase of the compressive strength. However, it caused a noticeable decrease in bending strength. The microstructure of geopolymer indicated that the degree of polymerization and cohesion of geopolymer have systematical depending on these critical molar ratios, making the mechanical properties of geopolymer susceptible to different types of loads. This paper reveals the relationship between the microstructure of geopolymer and different mechanical properties and helps to selectively prepare corresponding geopolymer for different loading patterns.
Highlights
Geopolymer is a kind of calcium-free inorganic silicaalumina cementitious materials, which involves the chemical reaction of alumino-silicate oxides with alkali polysil-Davidovits et al [1] proposed that the amorphous to semi-crystalline three-dimensional silico-aluminate structures, the products of polymerization reaction, are of the Poly(sialate) type, the Poly(sialate-siloxo) type, the Poly(sialate-disiloxo) type, whose formation has important connections with S/Al, Na/Al and H/Na molar ratios [9]
The experimental results showed that compressive strength and bending strength of geopolymer has an opposite reaction under different critical molar ratios
The microstructure of geopolymer indicated that the degree of polymerization and cohesion of geopolymer have systematical depending on these critical molar ratios, making the mechanical properties of geopolymer susceptible to different types of loads
Summary
Geopolymer is a kind of calcium-free inorganic silicaalumina cementitious materials, which involves the chemical reaction of alumino-silicate oxides with alkali polysil-Davidovits et al [1] proposed that the amorphous to semi-crystalline three-dimensional silico-aluminate structures, the products of polymerization reaction, are of the Poly(sialate) type, the Poly(sialate-siloxo) type, the Poly(sialate-disiloxo) type, whose formation has important connections with S/Al, Na/Al and H/Na molar ratios [9]. Duxson et al [20, 21] studied effects of Si/Al and Na/K on the microstructure and mechanical properties of geopolymer and found that as Si/Al increased, compressive strength and Young’s modulus increased and decreased, and reached the maximum when Si/Al reached 1.90 and Na/K was 0.5/0.5. He et al [22] found that as the Si/Al increased from 2 to 4, the molecular structure changed, resulting in a gradual increase in flexural strength and Young’s modulus. It was found that High H2O/Na2O had a negative effect on the degree of polymerization thereby leading to low compressive strength due
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