Preparation And Properties Of Environmental-friendly Permeable Bricks From Dredged Soil By Non-fired Method

In recent years,China's annual dredging volume has exceeded 1 billion m3.Dredged soil is difficult to be directly treated and utilized because of its large amount,complex composition and fluidized shape,and it is easy to cause secondary environmental pollution.Meanwhile,the demand of building materials including sand and stone is increasing day by day,and it has been reached more than 10 billion tons every year.A large number of non-renewable mineral resources have been over-exploited,thus seriously affect the ecological environment.In addition,with the acceleration of urbanization,many kinds of concrete building materials with low permeability are used as the urban pavement,and the increasing of impervious and hardened pavement raises a series of urban problems such as urban "heat island" effect,surface runoff,and waterlogging.Furthermore,the self-circulation of water resources is seriously hindered in natural ecosystems.This study puts forward the preparation process of environmental-friendly permeable bricks using dredged soil in non-fired method,thus the technology can well solve the current problems of dredging industry,building materials industry and urban planning industry.The research content and results of this paper are as follows:(1)According to volume ratio,and the experimental proportion of the preparation of dredged sludge non-fired wrapped-shell aggregates permeable brick(DSPB)was determined.Four types of the dredged sludge non-fired wrapped shell aggregates(WSLAs)were prepared by non-fired method:TH-WSLAs-F,TH-WSLAs-C,TJ-WSLAs-F,and TJ-WSLAs-C.The basic properties of the four kinds of WSLAs were characterized,such as bulk density,apparent density,void fraction,compressive strength,water absorption and frost resistance.The results show that the properties of WSLAs meet the national standard(GB/T 17431-2010),and the proportion of four kinds of WSLAs to produce DSPB is enumerated according to the calculation of volume method.(2)The preparation technology of DSPB was studied.TH-WSLAs-F,TH-WSLAs-C,TJ-WSLAs-F,TJ-WSLAs-C were used as aggregate to prepare four types of DSPB:TH-DSPB-F,TH-DSPB-C,TJ-DSPB-F,and TJ-DSPB-C.The effects of water-binder ratio,molding pressure,target porosity,fly ash content,aggregate particle size and aggregate type on the strength and permeability of DSPB were discussed in detail.The results show that TJ-DSPB-F was optimized under the conditions:water cement ratio of 0.34,molding pressure of 3 MPa,target porosity of 15%and fly ash content of 10%,and the compressive strength and permeability of TJ-DSPB-F are 12.6 MPa and 0.202 mm/s,respectively.(3)The mechanical properties and durability of DSPB were analyzed theoretically.Based on the optimal process,the compressive strength,water permeability,freeze-thaw resistance,blockage resistance and erosion resistance of DSPB were analyzed,and the microstructure of DSPB was characterized by scanning electron microscopy(SEM).The results show that:the joint strength of connection point of WSLAs is closely related to the strength performance of DSPB,and the point connection is more susceptible to the influence of external conditions.The main performance i5 the appearanee of micropores and cracks in the cement stone,and the number,width and development trend of micropores and cracks directly determine the extent of performance damage of DSPB.Moreover,in the simulated environment water,there is no harmful extract in DSPB,which meets the requirements of GB 3838-2002.(4)The effect of admixtures on DSPB properties was investigated.In combination with physical and chemical enhancement,admixtures such as fiber and water-proofing agent were introduced in the study.The strength performance and freeze-thaw resistance of DSPB were studied,and the microstructure was characterized by polarizing microscope(PM)and scanning electron microscope(SEM).The results prove that DSPB was optimized under the conditions:GF content of 2.0 kg/m3,GF incorporation way of 3:7,10%concentration of silicone waterproof agent was added to the cementing material,and the compressive strength and permeability of DSPB are 16.4 MPa and 0.202 mm/s respectively.Compared with the previous process,the strength of DSPB is greatly enhanced and improved upon 30.2%under the condition that the permeability coefficient is mostly unchanged.The essence of performance enhancement by adding additives is to prevent or delay the formation and development of micro-cracks at the point connections of WSLAs.