| As a kind of green building materials,recycled aggregate and recycled concrete are capable to promote the sustainable development of construction industry,which is an important development trend of building materials industry.Due to the construction waste has the characteristics of wide source,complex composition and difficult separation of multiple components,the recycled aggregate prepared by traditional aggregate production process has low quality and high volatility.The recycled concrete made of recycled aggregate has low performance and poor stability,which seriously influence the popularization and application of recycled aggregate,recycled concrete and their products.In order to improve the quality of recycled aggregates and recycled concrete,and broaden its application fields,it is urgent to solve the basic scientific problems such as the quality control technology of recycled aggregate and the mix proportion design method of recycled concrete.Supported by the National Natural Science Foundation of China(51378270),this thesis applied the combination of numerical analysis and theoretical analysis based on the experimental research.The technologies of performance improvement and quality control of recycled aggregate,the effect of quality and replacement rate of recycled aggregate on properties of recycled concrete were studied systematically,and the mix proportion design method for different kinds of recycled concrete was established,such as recycled coarse aggregate concrete,recycled fine aggregate concrete,and double mixed recycled aggregate concrete.The specific research contents include: physical strengthening,chemical strengthening and composite strengthening were carried out for the simple crushing recycled aggregate prepared from the waste concrete materials.The effects of various strengthening technologies on the properties of recycled aggregate were studied systematically,and the strengthening technology of recycled aggregate was optimized based on the effect of different strengthening technologies on the properties of recycled concrete.Taking recycled aggregates after different strengthening technologies as the research object,and the influence of the quality and replacement rate of recycled aggregate on the performance of recycled concrete was emphatically studied.Taking the mix proportion design method of ordinary concrete as reference,considering the different using state of recycled aggregate,the principles of water consumption and binder-water ratio for recycled concrete were determined,and the simple design method for the mix proportion of recycled concrete was proposed.The water consumption formula and strength formula of recycled concrete including multiple factors were established based on the theoretical analysis and experimental results,and the high precision design method for the mix proportion of recycled concrete is proposed.(1)The physical strengthening technology,chemical strengthening technology and composite strengthening technology of recycled aggregate were comparatively studied.Compared with simple crushing recycled aggregate,the physical strengthening treatment was mainly embodied in improving aggregate grain shape,optimizing particle gradation and reducing residual mortar adhesion of the recycled aggregate.The chemical strengthening treatment mainly reduced the water absorption of recycled coarse aggregate and the water demand ratio of recycled mortar of recycled fine aggregate,and less improvement effect on other performance indicators indexes of recycled aggregate.The composite strengthening treatment combined with the advantages of two kinds of strengthening technology significantly improved the quality of recycled aggregate and the performance of recycled aggregate.The recycled concrete was prepared by replacing natural aggregate with 100% recycled aggregate treated by different strengthening technologies,and the recycled aggregate strengthening technology suitable for recycled concrete was selected as the physical technology after compared its comprehensive properties.(2)The effects of the quality and replacement rate of recycled aggregate on the workability,mechanical properties and durability of recycled concrete were investigated under different dosage of cementitious materials,and thus the degradation mechanism of the recycled concrete performance were revealed.Compared with ordinary concrete,the addition of recycled aggregate had an adverse effect on the performance of recycled concrete.It mainly shows that the water consumption of recycled concrete was increased,the compressive strength was reduced,and the durability of resistance to chloride ion penetration,carbonization,frost resistance and shrinkage were low,but its compressive strength of three days and seven days increases greatly.Moreover,the performance changes of recycled concrete are closely related to the quality and the replacement rate of recycled aggregate.When the quality of recycled aggregate is higher and the replacement rate of recycled aggregate is lower,the performance of recycled concrete is close to that of ordinary concrete,and otherwise the difference between the performance of it and ordinary concrete is greater.(3)In view of the recycled coarse aggregate under the condition of natural environment,the saturated surface-dry and the absolute dry,the concept of external water consumption,effective water consumption,absolute water consumption and actual binder-water ratio,effective binder-water ratio and absolute binder-water ratio were introduced.The effect of recycled aggregate under different using states on the performance of recycled concrete was comprehensively analyzed,and the principles of water consumption and binder-water ratio were found based on the good linear relationship between water consumption of recycled concrete and replacement rate of recycled aggregate,as well as compressive strength to binder-water of recycled concrete.The principles of effective water consumption and absolute binder-water for the mix proportion design of recycled coarse aggregate concrete were proposed,and the simple design method for the mix proportion of recycled coarse aggregate concrete was established with reference to ordinary concrete.Based on the principles of absolute water consumption and absolute binder-water for the mix proportion design of recycled fine aggregate concrete,the simple design method for the mix proportion of recycled fine aggregate concrete was established.(4)Through composite material theory,the strength formula of recycled concrete was established with introducing the influence coefficient of absolute water consumption of recycled concrete and the impact factor on the strength of recycled aggregate by taking the common concrete as the base phase and the recycled aggregate as negative reinforced phase.The functional expressions of absolute water consumption influence coefficient of recycled concrete,the strength impact factor of recycled aggregate and the water absorption rate of recycled coarse aggregate or the water demand of recycled mortar of recycled fine aggregate were established respectively by systematically analyzing the effect of quality and replacement rate of recycled aggregate on workability and mechanical properties of recycled concrete.And the mix proportion design method for different kinds of recycled concrete with high accuracy were established based on the absolute water consumption formula and strength formula of recycled concrete with wide applicable range.In this thesis,the quality control technology of recycled aggregate and the design method for the mix proportion of recycled concrete were the key research.The strengthening technologies for the preparation of various quality recycled aggregate were explored,and the effects of different factors on the performance of recycled concrete were studied.The simplified mix proportion design method of recycled concrete based on the principles of water consumption and binder-water ratio and the precise mix proportion design method of recycled concrete based on absolute water consumption formula and strength formula were put forward respectively for the first time.Consequently,the quality control technology of recycled aggregate and the mix proportion design method of recycled concrete have significance for both popularizing recycled concrete and ensuring engineering quality. |
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