Study On The Mechanical Properties Of Lime-fly Ash Sulfoaluminate Cement Stabilized Loess Base

The addition of lime,fly ash,cement and other inorganic binders to loess forms the stabilized loess,which is often used as the road base and subbase material.However,practices have proved that when lime or lime-ash stabilized loess is used as a road base material,the early strength is low,and the opening time after paving is relatively late.For road base maintenance projects that need to open traffic as soon as possible,the use of stabilized loess is affected by big restrictions.The stable loess in seasonally frozen areas is often damaged by freeze-thaw cycles,and lime and lime and fly ash stabilized loess cannot be constructed under low-temperature conditions(≤5°C).Given the diseases of road base in spring thawing period,it is necessary to develop a kind of economical,eco-friendly and anti-freeze inorganic binder stabilized material to ensure that the road base can be maintained after paving in low-temperature period,and be characterized by fast hardening,early strength,the timely opening of traffic and good freeze-thaw resistance.Sulphoaluminate cement(SAC)has significant early strength,so it was added to the lime stabilized loess to improve the early strength of stabilized loess in this study.However,there are few studies on the mechanical properties of lime-fly ash-sulfoaluminate cement stabilized loess at home and abroad,and there is a lack of relevant researches on the quantitative evaluation of the mechanical properties of binder materials stabilized loess.This paper,therefore,a series of unconfined compressive tests,split tensile tests were carried out to explore the influences of SAC content,curing time and porosity on the unconfined compressive strength and split tensile strength of lime-fly ash-SAC stabilized loess.Also,the unconfined compressive strength tests were conducted on the specimens cured under low-temperature and suffered freezethaw cycle,respectively,to study the frost-resisting property and constructability of the stabilized loess under low-temperature conditions.The results of the unconfined compressive tests and split tensile tests indicate that the increasing curing time and decreasing porosity result in the continued growth of the unconfined compressive strength and splitting tensile strength of lime-fly SAC stabilized loess.The addition of sulfoaluminate cement(SAC)significantly improves the early strength of lime-fly ash-SAC stabilized loess.When curing time,porosity and inorganic binder content are constant,the unconfined compressive strength and split tensile strength increase with the increase of sulfoaluminate cement content;For a stabilized loess with an inorganic binder content of 30%and SAC content of 5% after 1 day of curing,the unconfined compressive strength is greater than 0.7MPa,which meets the requirements of the opening traffic.Therefore,lime-fly ash-SAC stabilized loess can be applied as an excellent road maintenance material.Through the analysis of test data,the relationships of unconfined compressive strength and split tensile strength versus the key influencing factors(binder content,curing time,porosity)were established for lime-fly ash-SAC stabilized loess,which provides a reference for the reasonable selection of the amount of binder,the degree of compaction and the curing period.Finally,based on the MohrCoulomb theory,a simple method for calculating c and φ of the stabilized loess is proposed herein,by which shear strength parameters can be obtained only requiring to conduct unconfined compressive strength or split tensile strength.The result of freeze-thaw tests shows that both the unconfined compressive strength and the mass of the stabilized loess specimens decrease with the increase of the numbers of freeze-thaw cycles,but the drop degree is relatively small for those of the stabilized loess with 30% inorganic binder content.But the mass loss rate of the specimens does not exceed 5%,which meets the needs of projects.Spalling phenomena were observed on the surface of the specimen with 20% the inorganic binder,while it does not occur for the specimen with30% inorganic binder content.When the stabilized loess with 30% binder content and 5% SAC content under low-temperature curing conditions after 4days of curing,the unconfined compressive strength under thawing conditions reaches above 0.8MPa;With the increase of SAC content,the strength increases significantly,and the unconfined compressive strength under unthawed conditions is higher than that under thawed conditions due to the action of ice.In spring,the road base is in the status of different thawing degrees due to the large temperature difference between morning and night,which causes the uneven load-bearing capacity for the road base,thereby resulting in the deformation and failure of roads more easily.