Study On Preparation And Properties Of Alkali Activated Slag-fly Ash-based Shield Muck Brick

There is 3 million m~3 muck(about 4.5 million tons)produced in the reconstruction engineering of Beijing East Sixth Ring Road(Beijing-Harbin Expressway～Luyuan North Street).In order to realize the resource utilization of shield muck,alkali-activated cementitious materials are used to prepare shield muck non-fired brick.Various testing methods are used to study and analyze the physical and chemical properties of shield muck,the working properties,mechanical properties,and drying shrinkage properties of alkali-activated cementitious materials are further investigated.On the basis of clarifying the properties of shield muck and alkali-activated cementitious materials,the mechanical properties,durability,and microscopic properties of laboratory static pressure formed alkali activated slag-fly ash-based shield muck brick are studied.Finally,optimize the test ratio and carry out practical production research on shield muck bricks.Clarify the feasibility and technical route of preparing non-fired bricks based on alkali-activated cementitious materials and provide reference for the resource utilization of similar shield muck in China.The main conclusions of the paper are as follows:Shield muck particles are fine,fineness modulus is 1.2,mud content is up to 17.5%,p H value is 7.6,it is weakly alkaline,water content is high,it hardens after air drying,and the main mineral components are quartz,albite and muscovite.The fluidity of alkali activated slag-fly ash paste changes between 130mm and 180mm,.The initial and final setting time of paste vary from 7 min to 42 min and from 12 min to 63min.Compressive and flexural strength of mortar increase with the increase of alkali content and slag content,and show a trend of first increasing and then decreasing with the increase of sodium silicate modulus.The drying shrinkage of mortar increases with the increase of alkali content,sodium silicate modulus and the relative content of slag and fly ash.Compressive strength of alkali activated slag-fly ash-based shield muck brick increases with the increase of slag and fly ash-muck ratio.When slag and fly ash-muck ratio increases from 1:6 to 1:1.5,the 28-day compressive strength of shield muck brick increases from6.8MPa to 50.4MPa.When the relative content is 9:1,the compressive strength of shield muck brick first increases and then decreases with the increase of alkali content.When the alkali content increases from 3%to 7%,the 28-day compressive strength of muck brick increases from 23.0MPa to 47.0MPa,and when the alkali content increases from 7%to 9%,the compressive strength decreases from 47.0MPa to 38.1MPa.The Compressive strength of three groups of alkali activated slag-fly ash-based shield muck bricks by laboratory static pressure molding is 1.28～1.75 times that of cement-based bricks.The strength loss rate of alkali activated based shield muck bricks subjected to high temperature of 800℃is 64.4～75.1%,while the strength loss rate of cement-based muck bricks is 100%.Under the high temperature of 800℃,solid phase reaction occurs in the hardened structure of alkali activated slag-fly ash paste and a large amount of gehlenite is generated,while the hardened structure of cement paste is loose and porous,and the gel product completely loses its gelling ability.The more slag content is added,the better the frost resistance of shield muck bricks.After 80 freeze-thaw cycles,the strength loss rate of three groups of alkali activated based muck bricks is 18.3～29.4%,while the maximum strength loss rate of cement-based muck bricks is 42.2%.When alkali content is 7%,sodium silicate modulus is 1.1,slag and fly ash-muck ratio is1:5,water-solid ratio is 10%,and relative content of slag and fly ash is 9:1,28-day compressive strength,water absorption,softening coefficient,mass loss rate after 25 freezes,and compressive strength value after freezing of alkali activated based muck bricks by factory vibration pressure molding are 32.4MPa,4.2%,0.95,0.9%,and 29.6MPa,respectively,all properties meet the requirements of MU25 in JC/T 422-2007 Non-fired rubbish gangue bricks.However,the performance of cement-based muck brick in the control group only meets the requirements of MU15.