| Waste electric poles belong to a kind of concrete solid waste,and crushing waste poles to prepare recycled fine powder can improve resource utilization and achieve sustainable development.And the production of gypsum slag cement has low energy consumption and low emission,and the cement has good mechanical properties,which is a kind of low-carbon cement.Compounding recycled fine powder with gypsum slag cement as cementitious material completely replaces ordinary silicate cement in the preparation of concrete,which can reduce the cost of concrete production and also realize the regeneration of waste resources,which has important social and economic benefits.Therefore,in this paper,the performance characteristics of concrete with high solid waste content were investigated using recycled fine powder compounded with gypsum slag cement as cementitious material.Firstly,a study on the composite of recycled fine powder and gypsum-slag cement was conducted.Mechanical refinement and heating excitation were used to activate the regenerated fine powder.The best activation of the regenerated fine powder is to ball mill the regenerated fine powder for 80 minutes and then calcine it at700℃for 2h.As a result,a regenerated fine powder with an activity index of 73%can be obtained.Further colloidal tests showed that the workability of the mortar gradually deteriorated and the 28d compressive strength gradually decreased with the increase of the regenerated fine powder admixture.Next,a study of the properties of concrete prepared by combining recycled fine powder with gypsum-slag cement was conducted.Specifically,recycled fine powder was compounded with gypsum-slag cement as cementitious material to completely replace conventional cement in the preparation of concrete specimens.The results showed that the apparent density of concrete decreased,the water absorption rate became larger and the 28d compressive strength decreased gradually with the increase of recycled fine powder admixture.When the amount of recycled fine powder reached30%,the apparent density of concrete decreased to 2050kg/m3,the water absorption increased to 6.0%,and the 28d strength decreased from 53.8MPa to 38.4MPa.The amount of recycled fine powder admixture also has an effect on the durability of concrete,when the concrete is admixed with 20%fine powder,at which time the concrete has the lowest dry shrinkage rate;when 10%fine powder is admixed,the concrete has the highest carbonation resistance.In order to optimize the concrete ratio,this paper also studied the effect of water-cement ratio and sand rate on the performance of concrete.When the sand rate was controlled to 35%,the mechanical properties and carbonation resistance of concrete were optimal.Finally,a study on the modification of the properties of concrete prepared by Silica fume was incorporated to improve the compressive strength and carbonation resistance of the concrete,but the dosage should not be too high,and the best dosage was 5%,when the 28d compressive strength of the concrete reached 46.9MPa and the28d carbonation depth decreased to 10.5mm.Combining recycled fine powder with gypsum-slag cement was carried out.Specifically,the modifying effects of silica fume,nano-Si O2（NS）and nano-Al2O3（NA）on concrete were investigated.The modification effect of NS was better than that of silica fume,and its optimal dosage was 2%,when the 28d strength of the concrete reached 50.7MPa and the 28d carbonation depth decreased to 7.5mm.NA has the best modification effect,and its optimal dosage is3%,when the concrete 28d strength can reach 55.3MPa,and the 28d carbonation depth is reduced to 6.5mm.Further microscopic tests showed that they all reduce the porosity and improve the pore structure of concrete,and can induce the generation of more hydration products.However,all three modifiers adversely affected the dry shrinkage of concrete,and the higher the amount of admixture,the greater the dry shrinkage. |
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