| Cement-soil is often used to deal with low-strength,high-compressibility soft soil foundation,but there are still problems such as insufficient strength and excessive deformation in actual engineering.Therefore,the fly ash and fibers are used to improve its mechanics performance and deformation characteristics,which has been greatly applied in engineering practice.In this paper,unconfined compression test,splitting tensile test,and SEM test of cement-soil with different contents of polypropylene fibers(0.0.1%,0.2%,0.3%,0.4%,0.5%)and fly ash(0,4%8%,12%,16%,20%)were carried out.Then based on most appropriate content of polypropylene fiber and fly ash,the durability test of cement-soil with different solutions(water,4.5 g/L,18 g/L,30 g/L sodium chloride solution),freeze-thaw cycles(0,1,3,6,10,15 times),dry-wet cycles(0,4,8,12,16,20,28 times)are performed.(1)Unconfined compression test and splitting tension test of cement-soil with different polypropylene fiber and fly ash contents were carried out.The unconfined compressive strength,splitting tensile strength,peak strain and failure mode of cement-soil modified with polypropylene fiber and fly ash were analyzed.The results show that with increasing polypropylene fiber and fly ash contents,both the unconfined compressive strength and the radial splitting tensile strength of cement-soil tend to increase first and then decrease.When the polypropylene fiber content is 0.4%and the fly ash content is 8%,the unconfined compressive strength and radial split tensile strength are 4.90 MPa and 0.91 MPa,respectively,which increases 32.79%and 51.67%compared with ordinary cement-soil.Meanwhile,peak strain under unconfined compression and splitting tension test are 0.0410 and 0.0196,which are 20.94%and 68.97%higher than the ordinary cement-soil,respectively.The stress-strain curve of cement-soil modified with polypropylene fiber and fly ash can be divided into compaction stage,elastic stage,plastic stage and failure stage.The addition of polypropylene fiber and fly ash improves the deformation characteristics of cement-soil to a certain extent.(2)Under the coupling effects of chloride salt erosion and freeze-thaw cycles,the mass change rate,P-wave velocity,unconfined compressive strength,and deformation modulus of cement-soil before and after freeze-thaw were obtained.The microstructural damage characteristics-were analyzed,and relationship between confined compressive strength of cement-soil and the number of freeze-thaw cycles were established.The results show that as the number of freeze-thaw cycles increases,the unconfined compressive strength of cement-soil in water,4.5 g/L,18 g/L,and 30 g/L sodium chloride solutions decreases overall.After 15 freeze-thaw cycles,the unconfined compressive strength of cement-soil in water,4.5 g/L,18 g/L,and 30 g/L sodium chloride solutions decreased by 64.10%,67.82%,69.15%and 71.01%compared with that before the freeze-thaw cycle,respectively.As the chlorine salt concentration increases,the ability of cement-soil to resist freeze-thaw corrosion becomes weaker.In addition,the deformation modulus gradually decreases and the microscopic damage inside the cement-soil becomes more serious.Under the same number of freeze-thaw cycles,the damage of cement-soil subjected to the coupling effects of sodium chloride solution and freeze-thaw cycles is greater than that of cement-soil in clean water.(3)With increasing the chloride salt concentration and the number of dry-wet cycles,the mass loss rate of cement-soil increases and the P-wave velocity decreases.Compared with the unsoaked state,the chlorine salt soaking has a degrading effect on the unconfined compressive strength of cement-soil,and the unconfined compressive strength has an exponential decrease relationship with the number of wet-dry cycles.After 28 wet-dry cycles,the unconfined compressive strength of cement-soil in water,4.5 g/L,18 g/L and 30 g/L sodium chloride solution decreases by 48.79%,52.63%,56.88%and 57.89%,respectively.As the chlorine salt concentration increases,its deformability gradually softens,and the degree of erosion becomes more severe.SEM images show that chloride salt erosion and wet-dry alter internal microstructure of cement-soil.Under the soaking of water and chloride salt solution,the cementitious material inside cement-soil dissolves and loses,and the internal minerals react to form soluble substances,which induces the expansion and penetration of cracks and pores,leading to decrease macro strength and increase deformation.Figure[52]Table[16]References[88]... |
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