Experimental Study On Properties Of Modified RAW Soil Material

Raw soil material has a long history and the raw soil building was the earliest form of human architecture.However,people have gradually stopped the use of raw soil materials because of its low strength as well as the poor performance of water or earthquake-resistance and people nowadays rarely live in the earth-based buildings any more.In order to expand the use of raw soil materials,cut the cost and improve the retrievability,raw soil material strengthening has become very important.In this paper,phosphogypsum,fly ash,lime and cement as well as geoploymeric,CMC and potassium silicate was used as modified raw material.The samples of modified raw materials were prepared by pouring and ramming separately.The mechanical properties,water resistance,thermal properties and reclamation characteristics of the samples were tested at different ages.The effects of modified materials,molding process and curing conditions on the properties of raw soil were studied,and the corresponding modification mechanism was discussed based on the analysis of the micro-morphology.The paper indicates that a certain amount of phosphogypsum can increase the 28-day compressive strength of raw materials with a 10%cement content.And the optimal content of phosphogypsum is 5%.The addition of fly ash can improve the compressive strength of modified raw soil material.Compared to cement content of 10%,the highest 28-day compressive strength can be increased by 52%.The orthogonal test shows that the maximum 28-day compressive strength of the material is 18.55 MPa.The 28-day compressive strength ofmaterial by ramming moulding can be 170% higher than that of pouring moulding,reaching 7.21 MPa under the same curing condition.On the basis of orthogonal experiment,the effect of different modified materials on raw materials was studied by controlling variables.The curing conditions have a great influence on the properties of the raw soil material.The higher the temperature is,the greater the strength of the raw soil material will possess.The maximum compressive strength of this experiment is 23.72 MPa with 5% phosphogypsum mixed with 20% fly ash,3% lime and 8% cement at the curing condition of 85 ?,which meets the standard of MU20 sintered brick.The addition of phosphogypsum,fly ash,lime and cement can greatly improve the water-resistance of the raw soil,and the higher the curing temperature is,the stronger the water-resistance is.When the curing temperature exceeds 70 ° C,the softening coefficient of the material will be higher than 0.9.When the curing temperature exceeds 85 ° C,the water absorption of the material will meet the requirements of sintered bricks.After modification,the original physical structure,thermal properties and pH value of the raw soil materials will stay the same,which ensures that the modified raw soil material can be recycled.The testing results indicated that geopolymeric cement mixed with of harder can improve the strength and water resistance of the raw soil material.The bast compressive strength of pouring experiment is 17.8MPa with 75% raw soil mixed with 16.7% metakaolin,8% alkali-activator and 10% potassium silicate,which meets the standard of MU15 sintered brick.The softening coefficient of the material is 0.88,which meets the requirements of wall materials of water resistance.In the paper,the more CMC is added to the raw soil material,the higher the strength is,as well as the moisture content and the water resistance.While 0.5% potassium silicate is enough for a good modification effect.The bast compressive strength of rammed experiment is 6.48 MPawith 1.5% CMC mixed with 0.5% potassium silicate and 22% moisture content.