Porous concretes such as aerated and lightweight concretes are commonly used in construction fields. Lightweight construction materials are used to reduce either the weight or the budget of building structures. Porous concrete production is widely utilised aluminium (Al) powder to increase pores in concrete structures and giving information for porous geopolymer production. It was introduced by adding 0.05-1% Al-powder as the initiated materials of geopolymers, to react with water in those materials and promote hydrogen gas inside specimens. The research, therefore, focused on the synthesis of porous geopolymer by metakaolin as a pozzolan and mixed with alkali solution (8M NaOH and Na2SiO3) as well as Al-powder as a foaming agent. The highly porous geopolymers were produced with various Al-powders as 0%, 0.2%, 0.4%, 0.6% 0.8% and 1% by weight. After 7, 14 and 28 days age, the specimens were tested the mechanical properties, such as compressive and flexural strengths. The water absorption, apparent porosity and bulk density were analyzed at 28 days age. The synthesis of metakaolin-based porous geopolymers with Al-powder presented good results. It showed that Al-powder content affected to degree of porosity of geopolymers. Keywords: Metakaolin based geopolymer, Porous geopolymer, Aluminium powder, Foaming agent, Mechanical and physical properties
The purpose of this research was to study pervious geopolymer concrete with different amounts of lignite fly ash (F), metakaolin (M), sodium silicate (NS) and 8 mol/L sodium hydroxide (NH) solution. Constant NS/NH ratio of 0.5, three alkali liquid/pozzolan (L/P) ratios viz., 0.5, 0.6 and 0.7 and pozzolan to coarse aggregate ratio of 1:8 were used. The compressive strengths of 50×50×50 mm3 cube specimens were tested at the age of 28 days. In addition, compressive strengths of 100 mm in diameter and 200 mm in height cylindrical specimens were tested at the age of 7, 14, 21 and 28 days. The chemical compositions and microstructures of specimens were characterized by X-Ray Diffraction (XRD) and Scanning Electron Microscope (SEM), respectively.The mixture with 50%F+50%M and L/P ratio of 0.7 was the best proportion for pervious geopolymer concrete according to the compressive strength, good permeability and microstructural images. The bond of Si-O-Al and Si-O-Si characterized by Fourier Transform Infrared Spectroscopy (FTIR) spectra confirmed the developed geopolymeric structure.
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