Experimental Study On Mechanical Properties And Durability Of Alkali Activated Metakaolin Cement Soil

Cement soil is widely used in the fields of foundation treatment,roadbed reinforcement and slope support,because of the advantages of convenient construction,low cost and small vibration.In view of the lack of strength and durability of pure cement soil,and in order to reduce the use of cement,this paper uses metakaolin to replace part of cement with equal amount,and improves its mechanical and durability properties under alkali excitation.Firstly,the unconfined compressive strength test was carried out on cement soil with different content of metakaolin and NaOH to determine the optimal content of metakaolin and NaOH.Then,based on the optimal content of metakaolin and NaOH,the effects of freeze-thaw cycles and dry-wet cycles on the durability of cement soil under different concentrations of NaCl were analyzed.Finally,combining with SEM analysis,the strengthening mechanism of cement soil and the mechanism of freeze-thaw damage and dry-wet deterioration under the erosion of different concentrations of NaCl are revealed.The main research contents are as follows:Firstly,through unconfined compressive strength tests,the effects of metakaolin content(0,1.5%,3.0%,4.5%)and NaOH content(0,0.75%,1.50%,2.25%)on the unconfined compressive strength and deformation characteristics of cement soil were analyzed.The results show that both metakaolin and NaOH can improve the compressive strength of cement soil.When metakaolin content is 3.0%and NaOH content is 1.50%,the compressive strength of cement soil reaches the maximum value,which is increased by 54.21%compared with that of pure cement soil.The stress-strain curve of cement soil shows a strain softening type,and the deformation modulus increases with the increase of the peak stress.Secondly,The effects of NaCl concentration and the times of freeze-thaw cycles(1,3,6,9 and 12 times)on the mass loss rate,strength and modulus of deformation of cement soil were investigated by the freeze-thaw cycle tests under different concentrations of NaCl(0.3g/L,9 g/L,18 g/L).The results show that when the concentration of NaCl is 0g/L and 3g/L,the mass loss rate of cement soil increases with the increase of the number of freeze-thaw cycles.When the concentration of NaCl is 9g/L and 18g/L,the mass loss rate of cement soil first increases and then decreases with the increase of the number of freeze-thaw cycles.The compressive strength and deformation modulus of cement soil decrease with the increase of the number of freeze-thaw cycles.Thirdly,The effects of NaCl concentration and times of dry-wet cycles(3,6,10 and 15 times)on the mass loss rate,strength and deformation modulus of cement soil were investigated by carrying out different dry-wet cycle tests under different concentration of NaCl(0,3g/L,9 g/L,18 g/L).The results show that the mass loss rate of cement soil first increases and then decreases with the increase of dry-wet cycles.The compressive strength and deformation modulus of cement soil generally decrease with the increase of the number of dry-wet cycles.The attenuation of compressive strength and deformation modulus mainly focuses on the first three wet-dry cycles.Finally,under the combined action of metakaolin and NaOH,the amount of hydration products in cement soil increased,while the number and diameter of pores decreased,which further improved the bonding ability between soil particles.The freeze-thaw and dry-wet cycles lead to cracks and holes in the cement soil,which weakens the integrity of the internal structure.At the later stage of freeze-thaw and dry wet cycles,NaCl enters the cement soil along the cracks and intensifies the development and expansion of internal cracks and pores.Figure[35]Table[8]References[82]...