The tuff powders with three particle sizes were alkali-activated using NaOH solution with a concentration of 7.5 mol/L and Na2SiO3 solution with a mass content of 2%.The effect of the particle size on the properties of geopolymer was investigated via a measurement of the setting time,density,vol-ume shrinkage,compression strength,flexural strength and Young's modulus after 28 days of curing.The results showed that,as the average particle size of the powder decreased to 5.133 μm,the condensation time of geopolymer decreased to 209 minutes,the density increased to 1 920.5 kg/m3 and the volume shrinkage rate increased to 15.65%.The compression strength,flexural strength and Young's modulus reached 63.334,12.794 and 735.38 MPa,respectively.As the particle size of powder decreased,the con-tact area between particles and activators increased.More gelling material was produced,and the contact between particles and gelling material changed from point contact to surface contact,which enhanced the cementation between the particles and significantly improved the pore structure.Compared with other geopolymers,it was found that the compressive strength of tuff-based geopolymer was more sensitive to particle size.The mechanical properties of geopolymer were more sensitive to average particle size when the critical particle size was lower than 30 μm.
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