Study On The Evaluation Method Of The Activity Of Recycled Concrete Powder

Recycled concrete powder(RCP)is a by-product with a particle size of less than 75μm produced during the recycling of waste concrete,and has a certain potential gelling activity.It is a new type of auxiliary cementing material,but the current evaluation of its activity is still based on the activity index method of fly ash,which has certain defects.Therefore,it is necessary to propose an appropriate activity evaluation method based on the characteristics of RCP.In this paper,the performance of representative RCP was comprehensively studied and analyzed,and the particularity of the active admixture of RCP was revealed.Various activity evaluation methods of active mixed materials at home and abroad were summarized,and the applicability of these methods to RCP was discussed and studied.On the basis of in-depth analysis of the concept of activity,a method for evaluating the activity of RCP was initially proposed,and the proposed method was demonstrated by using a representative RCP.The research content is as follows:(1).The RCP has different properties from other active materials.The main chemical composition of RCP is similar to cement,with good particle size distribution,and has the potential to replace cement as a cementitious material.Incorporating RCP into cement mortar will significantly reduce the fluidity and strength of the mortar,and the greater the amount,the greater the reduction.The strength of RCP mortar has a great relationship with the particle size distribution,and also has a certain relationship with its chemical composition.RCP has the following characteristics: large difference in composition,low activity due to more inert substances,composition related to particle size distribution,and large water demand,so the dosage should not exceed 40%.(2).Existing activity evaluation methods are not fully applicable to RCP.The activity index method is reasonable to evaluate the activity of RCP,but it cannot reflect the difference between RCPs and the time cost is too high.The(S+A+F)value in the active ingredient method has a certain correlation with the activity index,and the dissolution method,pozzolanic test method and electrical conductivity method cannot evaluate the activity of RCP.(3).Preliminary establishment of a method for evaluating the activity of RCP.The activity of RCP was divided into dilution effect(fd),physical effect(Δfp)and chemical effect(Δfc),which is expressed by the compressive strength of the 28 d specimen.The dilution effect is related to the amount of RCP;the physical effect is related to its physical properties;the chemical effect is related to its chemical activity.The physical effect of RCP generally reaches the maximum at 30% dosage,and the chemical effect generally reaches the maximum at the dosage of 25%~35%.The optimum dosage of RCP is recommended to be 25%~30%.(4).This method is suitable for the original RCP and is also expected to be suitable for the treated active RCP.