Study On Freeze-thaw-dry-wet Cycle Durability Of Alkali-activated Geopolymer Solidified Saline Soil

The use of alkali-activated geopolymers to solidify saline soil can effectively enhance the physical and mechanical properties of saline soil and control salinity,but solidified saline soil is used as an engineering soil.its durability plays a decisive role in the service life and safety of materials,and the salt content and types of salt in solidified saline soil are bound to affect the durability of solidified saline soil.Through the indoor freeze-thaw-dry-wet joint durability test,this paper deeply studies the deterioration characteristics of appearance,mass,volume,longitudinal wave velocity and unconfined compressive strength of solidified saline soil under the combined freeze-thaw-dry-wet cycle,and reveals the change law of pore structure and microstructure during the deterioration process.The effect of compound salinity on the durability of solidified saline soil is discussed.the conclusions are as follows:（1）The appearance,quality and volume stability of alkali-activated geopolymer solidified saline soil deteriorate in varying degrees with the increase of freeze-thaw dry-wet combined cycles.When the salt content is low（0.5%Na₂SO₄+1%Na Cl）,the appearance,mass and volume stability of solidified saline soil are higher than those of solidified non-saline soil.The appearance,mass and volume stability of other salt content were negatively correlated with salt content.（2）The longitudinal wave velocity and unconfined compressive strength of alkali-activated geopolymer solidified saline soil decrease with the increase of freeze-thaw-dry-wet combined cycles,and the attenuation degree of solidified non-saline soil and solidified saline soil with low salt content（0.5%Na₂SO₄ and 0.5%Na₂SO₄+1%Na Cl）is smaller.With the increase of Na₂SO₄ content,the attenuation degree of wave velocity and intensity increases,and with the increase of Na Cl content,the attenuation degree decreases at first and then increases.（3）With the increase of the number of freeze-thaw-dry-wet combined cycles,the BET specific surface area of alkali-activated geopolymer cured saline soil increased,and the average pore size of BJH decreased.With the increase of Na₂SO₄ content,the specific surface area increased and the average pore size decreased.With the increase of Na Cl content,the specific surface area increased at first and then increased.（4）The microstructure changes of different scales show that the nano-scale and micron-scale pores increase with the increase of salt content,especially the nano-scale cement structure is destroyed due to the freeze-thaw dry-wet cycle,resulting in the attenuation of strength.（5）The durability of alkali-activated geopolymer solidified saline soil decreases with the increase of Na₂SO₄ content,and increases at first and then decreases with the increase of Na Cl content.