Study On The Influence Of Admixture Of Slag On Physical And Mechanical Properties Of Weak Expensive Soil,with The Help Of Alkali-activator

Expansive soil has the characteristics of expansion and contraction,multi-fissures and so on.It is a typical "disaster soil" and has potential safety hazards to buildings.Alkali-activated slag can produce geological polymer with cementing ability,which can be used to improve the properties of Engineering materials.Taking expansive soils in Huainan City as the research object,the effects of slag added by 5%,15%,15%and 20%on plastic liquid limit,compressive strength,direct shear strength and expansion and contraction of expansive soils under 27.89%NaOH alkali excitation were studied.The main conclusions are as follows:(1)The free swelling ratio of experimental soil is 54%,which belongs to weak swelling potentiality.(2)Compared with untreated expansive soil,the effect of slag on the liquid and plastic limit of expansive soil under alkali excitation is more obvious;the plastic limit of expansive soil decreases with the increase of slag content,while the liquid limit increases first and then decreases with the increase of slag content.(3)Compressive strength and direct shear strength of untreated expansive soil and expansive soil improved by alkali-activated slag increase with age,and the growth trend is faster before 7 days and slower after 7 days.With the increase of slag content,the compressive strength and direct shear strength of expansive soil improved by alkali-activated slag increase.(4)Compared with the untreated expansive soil,the expansion and contraction of the expansive soil improved by alkali-activated slag is significantly reduced,and with the increase of slag content,the expansion and contraction of expansive soils have a decreasing trend.When expansive soil improved by alkali-activated slag(20%)is cured for 14 days,the free swelling ratio decreases by 70.4%,the linear shrinkage rate and volume shrinkage rate decrease by 75.7%and 72.6%,respectively.(5)The scanning electron micrograph of expansive soil modified by alkali-activated slag show that geopolymer is formed on the surface of expansive soil particles,and with the increase of curing time and slag content,the structure of the Geopolymers becomes dense.However,because of the alkali-activated slag,the microstructure of the expansive soil is cracked,and its cementing ability to soil particles is limited.This is likely to be the reason why the compressive strength and direct shear strength of the expansive soil are not improved at the same age during indoor curing for 14 days.(6)The XRD test of expansive soil showed that the crystal amount of CSH(calcium silicate hydrate)formed by NaOH alkali-activated slag in the mineral component of expansive soil is added with the increase of slag content and the curing timeThe study shows that alkali-activated slag can effectively alleviate swelling and shrinkage of expansive soil under the condition that the strength of expansive soil is not greatly affected,and it may become an effective method for improving expansive soil.Figure[32]table[17]reference[69].