Study On Mechanical Properties,shrinkage Properties And 3D Printability Of Glazed Hollow Bead Recycled Fine Aggregate Thermal Insulation Concrete

Glazed hollow bead is a kind of thermal insulation material with good thermal insulation performance.Glazed hollow bead thermal insulation concrete with good mechanical properties and thermal insulation performance has become a hot spot in the field of building thermal insulation research.With the renewal and iteration of new and old buildings in cities,a large amount of construction and demolition waste is produced.The researchers have successfully replaced the natural coarse aggregate in glazed hollow bead thermal insulation concrete with recycled aggregate from construction and demolition waste and prepared a green and energysaving recycled aggregate thermal insulation concrete.However,in addition to recycled coarse aggregate,recycled fine aggregate accounts for about 25%-50%of the total mass of construction and demolition waste.These recycled fine aggregate are not only varied in type,but also of different quality.As the elastic modulus of recycled aggregate is lower than that of natural aggregate,water absorption of recycled aggregate is higher than that of natural aggregate.Therefore,the shrinkage of recycled concrete prepared with recycled aggregate is generally greater than that of natural concrete.However,concrete shrinkage is the main cause of microcracks and macro-cracks in precast elements,which plays an important role in the ultimate design state of precast members.At present,there is no research on shrinkage of glazed hollow bead recycled insulation concrete made of recycled fine aggregate.In this study,two different types of glazed hollow bead recycled fine aggregate thermal insulation concrete were prepared and their shrinkage properties were studied.Based on functional gradient theory,the recycled fine aggregate thermal insulation concrete wall which can be used in 3D printed concrete system was designed.1.In this study,the recycled fine aggregate of waste concrete and recycled fine aggregate of waste clay brick were selected to replace the natural fine aggregate in glazed hollow bead thermal insulation concrete with different replacement ratio(25%,50%,75%and 100%).It was found that 50%was the optimal replacement ratio of the recycled fine aggregate of waste concrete and 75%was the optimal replacement ratio of the recycled fine aggregate of waste clay brick by studying the mechanical properties and drying shrinkage properties of glazed hollow bead recycled fine aggregate thermal insulation concrete.Due to the influence of water absorption of recycled fine aggregate,the drying shrinkage of recycled fine aggregate concrete with vitrified microbeads appears an obvious delay phenomenon.The shrinkage model of recycled fine aggregate concrete with vitrified microbeads established based on the experimental phenomenon can effectively predict the drying shrinkage strain of concrete.The specific expression is as follows:#122.On the basis of Study 1,the optimal replacement ratio of recycled fine aggregate of waste concrete(50%)and recycled fine aggregate of waste clay brick(75%)were selected.The influence of glazed hollow bead with different content(100%,130%,160%)on the mechanical properties and total shrinkage strain of recycled fine aggregate thermal insulation concrete was quantified.Based on the test results,the expression of the influence coefficient kb of glazed hollow beads was determined by regression analysis as kb=-4.4×104 rb2+8.65 × 10-2 rb-1.06.3.In order to realize the printing of recycled fine aggregate thermal insulation concrete wall,based on functional gradient theory,a recycled fine aggregate thermal insulation concrete wall suitable for HC-3DPRT concrete 3D printing system was designed.Through the study found that,compared with recycled fine aggregate thermal insulation concrete and decoration mortar prepared by recycled fine aggregate of waste concrete,although the recycled fine aggregate of waste clay brick has good initial fluidity and consistency,but with the development of the time,the fluidity and consistency of recycled fine aggregate thermal insulation concrete and decoration mortar prepared by recycled fine aggregate of waste clay brick decline faster,less printable property.In terms of mechanical properties of recycled fine aggregate thermal insulation concrete wall,each part(recycled fine aggregate thermal insulation concrete,thermal insulation mortar and decorative mortar)has good mechanical properties,and the transition zone also has good three-way mechanical properties,which meets the requirements of practical engineering.