| The contradiction between energy consumption,pollutant emission and ecological carrying capacity in China is becoming increasingly prominent.It is urgent to improve the utilization rate of solid waste resources and increase the preparation and application of recycled aggregate concrete,etc.Residual mud is a kind of solid waste with huge output.The characteristics of high moisture content,low activity and strength of residual mud lead to low resource utilization rate of residual mud.Recycled powder is a kind of fine powder solid waste.The characteristics of extremely fine particles,extremely low moisture content and complex composition of recycled powder lead to the current treatment method of recycled powder being stockpiling,resulting in dust and waste of resources.Therefore,it is imperative to improve the resource utilization rate of residual mud and recycled powder.The recycled powder is used to adjust the moisture content of the residual mud.The sinter-free aggregate of magnesium oxychloride cement was prepared by using residual mud and recycled powder as raw materials and magnesium oxychloride cement as the main curing agent,and then the sinter-free aggregate concrete was prepared by replacing the natural aggregate with the sinter-free aggregate.Recycled powder foamed concrete was prepared by replacing composite admixtures（fly ash and silica fume）with recycled powder with extremely fine particles.This is a new way to realize the reduction,harmless and resource utilization of residual mud and recycled powder.At the same time,it can effectively save natural resources,reduce energy consumption and CO2 emissions in the construction industry.The physical properties,chemical composition and particle size distribution of residual mud and recycled powder were studied.The low carbon cement-magnesium oxychloride cement was used as the main curing agent to solidify the residual sludge.Taking the compressive strength,softening coefficient and 3d heat release and heat release rate of magnesium cement solidified sludge as indexes,the benchmark ratio of magnesium cement solidified sludge was determined.The recycled powder was used to adjust the moisture content of the residual mud,and then the magnesium oxychloride cement was used as the main curing agent to solidify the residual mud and the recycled powder and prepare the magnesium cement sinter-free aggregate.The water absorption rate,cylinder compressive strength,softening coefficient and hydration products of the magnesium cement sinter-free aggregate were used as indicators to determine the sinter-free aggregate with the best performance.To prepare sinter-free aggregate concrete by replacing 5～10mm coarse aggregate with the best performing sinter-free aggregate,and to compare the effects of different sinter-free aggregate replacement rates on the basic properties and mechanical properties of sinter-free aggregate concrete.Different density grades of recycled powder foam concrete were prepared by replacing composite admixtures（fly ash and silica fume）with recycled powder,and comparing the effects of different recycled powder replacement rates on the basic properties,mechanical properties,thermal conductivity and pore size distribution of recycled powder foam concrete.The main conclusions are as follows:（1）The initial moisture content has a great influence on the compressive strength of magnesium cement solidified sludge.With the increase of initial moisture content,the compressive strength of magnesium cement solidified sludge gradually decreases,and the frosting and cracks on the surface of the specimen intensify.With the increase of magnesium cement content,the compressive strength of magnesium cement solidified sludge first leveled off and then increased rapidly.With the increase of the single substitution rate of fly ash and silica fume,the compressive strength of magnesium cement solidified sludge gradually decreases and tends to be flat,the softening coefficient gradually increases,and the 3d heat release and heat release rate gradually decrease.The optimum mix ratio of magnesium cement solidified sludge is that the initial water content is 16%,the magnesium oxychloride content is 20%,and the single substitution rate of fly ash and silica fume is 10%.（2）The addition of ammonium citrate and composite admixture has an effect on the properties of sinter-free aggregate.The 1h water absorption of sinter-free aggregate decreases,and the softening coefficient and compressive strength increase when single-doped ammonium citrate or double-doped ammonium citrate and composite admixture are mixed.The incorporation of composite admixtures increases the 1h water absorption,softening coefficient and compressive strength of sinter-free aggregate.The incorporation of ammonium citrate and composite admixtures increases the degree of crystallization of the phase5 and reduces the formation of Mg CO3 crystallization.The properties of sinter-free aggregate meets the requirements of lightweight aggregate.The 1h water absorption,softening coefficient and cylinder compressive strength of sinter-free aggregate with the best performance are 8.2%,0.46 and 22.0MPa,respectively.（3）With the increase of the replacement rate of sinter-free aggregate,the slump of sinter-free aggregate concrete increases gradually,the dry density decreases gradually,the water absorption rate decreases first and then increases,and the compressive strength increases first and then decreases.The maximum replacement rate of sinter-free aggregate is 25%.At this time,the slump of sinter-free aggregate concrete is 101mm,the 28d compressive strength is 29.0MPa,the dry apparent density is 2152kg/m3,the 24h water absorption is 5.3%,and the softening coefficient is 0.88.（4）With the increase of the replacement rate of recycled powder,the fluidity of recycled powder foam concrete gradually increases,the density and thermal conductivity first increase and then decrease and then increase,the water absorption first decreases and then increases,and the strength first increases and then decreases.When the replacement rate of recycled powder is 60%,the thermal conductivity of recycled powder foam concrete A03 is 0.0729W/（m·k）.When the replacement rate of recycled powder is 20%,the compressive strength of recycled powder foam concrete A07 is 5.46MPa. |
