Research On The Effect Of Completely Recycled Fine Aggregate Produced In Pilot Production On The Performance Of Building Mortar And C35 Concrete And Its Components

Waste concrete from construction waste is made into recycled aggregate.It can effectively alleviate the problem of construction waste siege and concrete sand aggregate shortage.The usual method of recycling waste concrete is to prepare it as recycled coarse aggregate and recycled fine aggregate.However,due to the poor performance of recycled fine aggregate,only recycled coarse aggregate can be reused in concrete,which makes only about 50% of the waste concrete can be reused in concrete.In order to make full use of the waste concrete,South China University of Technology proposed the idea of completely recycled fine aggregate(CRFA)--all the waste concrete is made into recycled fine aggregate less than 5mm.Compared with the traditional recycled fine aggregate,CRFA has the characteristics of high apparent density and low water absorption,and can completely replace the river sand and mechanism sand to make mortar and concrete.South China University of Technology has carried out pilot production test of fully regenerated fine aggregate in the early stage,obtained the optimal pilot production process,and put forward the concrete mix design for CRFA.Aiming at the construction mortar and C35 concrete with wide range,this paper systematically studies the influence of CRFA on the performance of building mortar,C35 concrete and concrete columns on the basis of the previous research.This paper also puts forward its application method in building mortar and concrete,and analyzes the benefits of completely recycled fine aggregate from the economic,environmental and social perspectives.The main research work and conclusions of this paper are as follows:(1)A series of experiments designed to produce common building mortars(including masonry,plastering and ground mortar)by completely replacing river sand with CRFA under 6 kinds of cement dosage.The results show that:1)By adjusting the water consumption and the amount of additives,CRFA mortar with the consistency of river sand mortar can be obtained.Compared with river sand mortar,it has better water retention,lower 2h consistency loss rate and similar compressive strength;2)Within the same cement dosage and consistency range,the water consumption of CRFA mortar is higher than the river sand mortar,mainly because of the high water absorption of CRFA;3)Autoclaved aerated concrete block masonry with CRFA masonry mortar has mechanical properties similar to that of river sand masonry mortar.The compressive strength and shear strength of masonry can meet the standard requirements.It can be used for autoclaved aerated concrete block masonry and can be designed according to the existing specifications;4)The working and mechanical properties of masonry,plastering and ground mortar prepared by CRFA instead of river sand can meet the requirements of Ready-mixed Mortar(GB/T 25181-2010),and the application of completely regenerated fine aggregate instead of river sand in building mortar can be adopted.(2)According to the results of a series of experiments on the mix ratio of fully regenerated fine aggregate to commonly used building mortars(including masonry,plastering and ground mortar)in the production of river sand,a mix ratio design method for CRFA building mortars is proposed.The steps are as follows: 1)Calculate the mortar test strength;2)According to the type of mortar tested,the regression formula of mortar strength and cement dosage is selected,and the cement dosage is calculated by mortar strength;3)The amount of sand is the density of CRFA loose accumulation;4)Determine the amount of admixture;5)According to the type of mortar tested,select the corresponding regression formula of cement dosage and water consumption,and calculate the water consumption through cement dosage;6)According to the measured apparent density,check the amount of each material to get the final mix ratio.(3)Designing the C35 grade of CRFA concrete and river sand concrete,on the mechanical properties,durability and the stability of the volume of contrast test,the results show that in the C35 strength: 1)In the case of 28 d compressive strength is,the whole strength of CRFA concrete after the age of 28 d growth is slower than the river sand concrete,lead to their 360 d age is slightly lower than the river sand concrete compressive strength,splitting tensile strength is slightly higher than river sand concrete at the same time,the elastic modulus and its equivalent;2)The durability of CRFA concrete is similar to that of river sand concrete,among which the frost resistance of CRFA concrete is slightly better than that of river sand concrete,and the chloride ion resistance is slightly worse;3)The 7d self-shrinking deformation of CRFA concrete is smaller than that of river sand concrete;At the early stage(before the age of 7 days),the drying shrinkage is smaller than that of river sand coagulant,and is larger than that of river sand concrete at 360 days.4)The anti-cracking performance of CRFA concrete is similar to that of river sand concrete,and no cracking occurs at the age of 15 days.(4)By C35 CRFA concrete and river sand concrete axial compression columns,the bearing capacity of large eccentric compression column experiment found that the recycled fine aggregate concrete axial compression columns and the failure process and failure mechanism of large eccentric columns and river sand concrete column basic same,its value is greater than the standard test bearing capacity calculation value,you can refer to the calculation method of normal concrete column in the current specification,estimate the carrying capacity of CRFA concrete column.(5)Because the price of CRFA is more than 50% lower than that of river sand,the cost of building mortar can be reduced by 32.6% ? 39.7% for the mortar with the same strength,and the cost of C35 CRFA concrete is 18.6% lower than that of river sand concrete.The use of CRFA has good economic benefits.(6)The 100% CRFA technology can use of waste concrete,and can replace all the fine aggregate of concrete and mortar,can achieve the purpose of cascade utilization of waste concrete,and can effectively reduce the consumption of natural aggregate concrete and mortar industry,social benefit and environmental benefit is remarkable,is conforms to our country city "without waste",new technology development trend of green building materials.