Experimental Study On Preparation Of Recycled Mortar By Construction Waste Recycled Fine Aggregate And Powder

With the acceleration of urbanization in China,the demolition of old cities has produced a large amount of construction waste.After the construction waste is crushed by the crusher,the recycled fine aggregates account for about 30%of the total quality of the construction waste,and the recycled fine powder accounts for about 15%of the total quality of the construction waste.The rational use of recycled fine aggregate and recycled fine powder to prepare recycled mortar is an effective measure to solve the problem of construction waste surrounding the city and polluting the environment.In this paper,classified recycled fine aggregate and recycled powder are used as raw materials to replace natural sand and as admixtures to prepare recycled mortar respectively,and the effects of classified recycled fine aggregate,recycled powder and vibration mixing on the basic properties of recycled mortar are discussed through the analysis of vibration mixing process and microstructure.The specific research contents and main conclusions are as follows:(1)Study on optimization of mix proportion of classified and recycled fine aggregate mortarThe water consumption of recycled mortar is higher than that of natural mortar,and the water consumption of Class III recycled fine aggregate mortar is greater than Class II.The water consumption per unit volume of recycled mortar increases with the increase of the replacement rate of recycled fine aggregate;the increase of the total amount of cement and fly ash can reduce the water consumption of the recycled mortar unit consistency.For RM10 and RM15 mortars,regardless of Class II or Class III recycled fine aggregates,the total amount of cement and fly ash is the most important factor affecting the compressive and flexural strength,and the effect of recycled fine aggregate replacement rate on compressive strength Secondly,the fly ash blending rate has the least influence on the compressive strength;while for the flexural strength,the fly ash blending rate has a greater effect than the recycled fine aggregate replacement rate.The recommended ratio of the compressive strength is recommended as the recycled mortar.The recommended mix ratio of RM10II mortar is:303kg/m~3 for the total amount of cement and fly ash,50%for the replacement ratio of recycled fine aggregate,and 10%for the blending ratio of fly ash;the recommended mix ratio for RM10III mortar is:303kg/m~3 for the total amount of cement and fly ash,30%for the replacement ratio of recycled fine aggregate,and 10%for the blending ratio of fly ash;the recommended mix ratio of RM15II and III mortar is:370kg/m~3 for the total amount of cement and fly ash,30%for the replacement ratio of recycled fine aggregate,and 10%for the blending ratio of fly ash.(2)Study on the effect of recycled powder admixture on the performance of recycled mortarThe larger the brick powder content in the recycled powder and the smaller the particle size of the recycled powder,the larger the water consumption of the recycled mortar unit consistency as the admixture.For the recycled mortar 3d,7d,28d compressive strength of recycled powder as the admixture,the optimum content of brick powder in different particle size recycled powder is different:the optimum content of 58-75?m is 30%,the optimum content of0-38?m and 38-58?m is 70%;no matter what kind of recycled powder is used as the recycled mortar of the admixture,the 28d compressive strength is the highest in the0-38?m particle size,that is,the smaller the recycled powder particle size,its activity effect and filling effect on the later strength of recycled mortar is greater.With the increase of the content of brick powder in the recycled powder,the trend of the effect of different size recycled powder on the flexural strength of recycled mortar is different.When the content of recycled powder of waste concrete is?70%,the 28d flexural strength of the recycled mortar as the admixture increases with the increase of the particle size of the recycled powder,and when the content of brick powder is?70%,the 28d flexural strength of the recycled mortar decreases as the particle size increases.(3)Influence of vibration mixing process on mechanical properties of recycled mortar and its microstructure analysisUnder the same ratio,the vibration mixing method is higher than the natural mortar for the 7d and 28d compressive and 28d flexural strength of the recycled mortar,and the RM15III mortar strength increase is higher than the RM15II mortar.This is because the natural sand particles are smooth,while the Class III recycled fine aggregates are rougher than the Class II recycled fine aggregates,and the internal micro-cracks are more.The vibration mixing can make the cement slurry more fully encapsulate the aggregate and improve the aggregate and the bond between the cementitious materials.Vibrating mixing makes the secondary interface more compact and more tightly bonded than the normal mixing method.At the same time,the vibration mixing destroys the cement agglomeration,which has a beneficial effect on the formation of C-S-H gel which contributes a lot to the bond strength,and improves the microstructure and strength of the regenerated mortar.