| In recent years,with the transformation and upgrading of cement products and concrete towards low-carbon environmental protection,green recycling and sustainable development,more and more solid waste materials have been used in the production of cement and sand aggregates.The resource properties are gradually revealed.In this paper,aiming at the problems of low activity of Yellow River sediment,large output and difficult utilization,combined with modern powder activity excitation technology,the potential activity of different grades of Yellow River sediment is stimulated to verify the feasibility of the synergistic excitation technology of acid-base activators.The activated Yellow River sediment was used as auxiliary cementitious material and fine aggregate in non-fired bricks,and the durability and economy of non-fired bricks were comprehensively evaluated.The research contents and results are as follows:（1）Through the interior design experiment,the cement and sand were replaced by the Yellow River sediment to prepare the mortar test block.Based on the theory of Fuller gradation,the optimal ratio of each particle size of the mortar was obtained,and the Yellow River sediment-cement mortar test block was prepared according to the standard method.The effects of different particle sizes and different amounts of sediment substitution on the properties of the mortar were analyzed.Taking the compressive strength of mortar as the evaluation criterion,the optimal replacement amount of each grain grade of Yellow River sediment to replace cement and fine aggregate was determined.The result shows:The optimal substitution rate of Yellow River sediment for cementitious material is 20%.The optimal replacement amount of 0.15～0.3 mm river sand by Yellow River sediment is 100%.（2）Taking the sediment of the Yellow River as the research object,its activity was stimulated by acid excitation-aging-alkali excitation technology.The excited Yellow River sediment with the same particle size was used to replace cement and sand to prepare a cement mortar test block,and its macroscopic（compressive strength,flexural strength,water absorption）and microscopic properties（porosity,pore distribution）data were measured.Combined with SEM,EDS and other analysis methods,the microstructure,the shape and composition of the product were analyzed.The result shows:The compressive strength,flexural strength and pore characteristics of the mortar test block stimulated by acid activator are improved.Acidic activators can damage the integrity and densification of Yellow River sediment particles,increase the specific surface area of particles and improve the reaction rate,which is conducive to the dissolution of active Si O2 and Al2O3and promote the hydration reaction.With the increase of aging time,acidic activators react more fully with Yellow River sediment,and the Yellow River sediment promotes the hydration reaction.Na2Si O3 has a dual excitation effect,which can effectively stimulate the potential activity of Yellow River sediment and improve the performance of colloidal sand test block.（3）The addition of an alkaline activator during the activation of the Yellow River sediment activity results in a high level of salinity and alkali content in the material,which may make the material more prone to efflorescence.Based on this,this section studies the effects of adding external admixtures,changing the curing method of the test block,and synergistic excitation of acid-base stimulants on the efflorescence behavior of the material.The result shows:The appropriate amount of fly ash can improve the strength and reduce the concentration of alkaline metal ions in the pore solution,so as to effectively control the occurrence of causticity.The acid and base co-excitation of Yellow River sediment can effectively promote the leaching of active ions from the Yellow River sediment and participate in the hydration reaction,thus reducing the content of free salt and alkali in the material and improving the overall density of the test block.The channel of salt and alkali in the material moving to the surface with free water is blocked,thus effectively improving the alkali spreading phenomenon of the material.（4）Taking the activated Yellow River sediment as the research target,it is applied to the field of non-fired brick materials.The compressive strength,water absorption and porosity of non-fired bricks were measured,and the phase and pore structure were observed by scanning electron microscope and nuclear magnetic resonance technology to study the influence of activated Yellow River sediment on the mechanical properties and durability of non-fired bricks.The result shows:The compressive strength and freezing resistance of the non-fired brick prepared by the Yellow River sediment after acid and base co-excitation are improved compared with those of the unexcited test groups,and the pore characteristics are also improved.The results show that the acid base activator co-excitation process can effectively stimulate the activity of Yellow River sediment,improve the morphology and quantity of hydration products,improve the pore characteristics of test blocks,and improve the strength and frost resistance of non-fired brick.（5）Through the analysis of the cost and social benefits of the non-fired bricks,explore the commercialization feasibility of the non-fired bricks.The results shows that:The cost of making non-fired brick by using Yellow River sediment instead of cementing material and fine aggregate is about 0.49 yuan/piece.Lower than the average cost of the market traditional red brick 0.55 yuan/piece;The non-fired brick can make large use of solid waste materials such as Yellow River sediment and fly ash,avoid the energy consumption and pollution gas generation of the firing process,turn Yellow River sediment waste into treasure in a green and environmental protection way,and realize the resource utilization of the waste. |
