Research On Preparation And Thermal Performance Of Broken Bridge Type Recycled Concrete Self-insulating Block

At present,the heat loss of the building external wall is relatively large.External wall insulation is generally divided into external insulation,internal insulation and self-insulation.The external insulation has poor durability and poor fire resistance;The internal insulation is easy to cause condensation on the inside of the wall.Self-insulation is the integration of insulation and structure.Compared with external wall insulation,it has the advantages of fast construction speed,low construction cost,life span the same of buildings,good durability and good fire resistance.In this study,a broken bridge-type self-insulating block was designed.The two thermal bridges of the concrete hollow block were broken to cut off the main path of heat transfer.The connecting structure with low thermal conductivity was used to connect the broken bridge.The heat insulation performance can be improved by this method.With the continuous development of my country’s urbanization,there are a huge amount of construction wastes,such as waste concrete and waste clay bricks.The recycling of waste concrete and waste clay bricks as aggregates of concrete has received increasing attention,but these two kinds of waste have low strength.In the glass fiber production process,a large number of waste glass fibers are inevitably produced.Glass fiber has the characteristics of high tensile strength.Consider adding glass fiber to recycled concrete to enhance the strength of the concrete,making recycled concrete,and then making self-insulating blocks.In this way,the developed self-insulating block realized the resource utilization of the above-mentioned three solid wastes.At the same time,the unique broken bridge design and reasonable block design make the self-insulating blocks suitable for construction.It’s thermal insulation performance to meet the requirements of the Shandong Provincial Residential Building Energy-saving Design Standard(DB37/5026-2014).In this paper,the influence of water-cement ratio,fly ash content,recycled coarse aggregate replacement rate,recycled fine aggregate replacement rate and glass fiber content on the thermal conductivity of recycled concrete was analyzed by orthogonal experiments.The significance of the influence of various factors on the thermal conductivity was analyzed by the range method and the variance method.The mix ratio with the lowest thermal conductivity was selected as the mix ratio for the self-insulating block.The influence of glass fiber content on the mechanical properties of recycled concrete was discussed.Then,mechanical and heat transfer performance test were performed with the broken bridge type self-insulating block made according to the mixture ratio determined by orthogonal test.Finally,the two-dimensional steady-state heat transfer simulation of the non-broken bridge block and the broken bridge block was carried out with ANSYS software.Simulation results included the temperature distribution diagram,the temperature gradient diagram in the Y-axis direction and the heat flow diagram in the Y-axis direction.Comparative test on thermal bridge was also carried out.The main research results were as follows:(1)The results of orthogonal experiments showed that:The best mix ratio determined was:cement:sand:waste fine concrete:waste coarse concrete:waste coarse clay brick:water:fly ash:glass fiber=1:0.87:1.30:1.63:1.63:1.17:0.19:0.02.Through range and variance analysis,the significance influence order(high to low)of various factors on the thermal conductivity of recycled concrete was:recycled coarse aggregate→recycled fine aggregate→water-binder ratio→glass fiber content→fly ash content.The concrete with the lowest thermal conductivity had compressive strength 17.3MPa,the flexural strength 4.07MPa,the thermal conductivity 0.485W/(m·K).(2)The results of the effect of glass fiber content on the mechanical properties of recycled concrete showed that:Under the same curing time,the compressive strength of recycled concrete decreased firstly,then increased and then decreased with the increment of glass fiber content.The highest 28-day compressive strength was 17.3MPa with glass fiber content 0.3%.It showed that adding a certain amount of glass fiber could enhance the compressive strength of recycled concrete,and the best glass fiber content was 0.3%.Under the same curing time,the flexural strength of recycled concrete increased first and then decreased with the increment of the glass fiber content.The maximum flexural strength of28-day was 4.07MPa with glass fiber content 0.3%.It showed that adding a certain amount of glass fiber could enhance the flexural strength of recycled concrete,and the best glass fiber content was 0.3%.(3)The results of the mechanical and thermal properties test of the broken bridge self-insulating block showed that:The average compressive strength of the block was5.85MPa and the average flexural strength was 2.61MPa.The heat transfer coefficients of the masonry envelope was calculated to be 0.380W/(m~2·K).The heat transfer coefficient values by test was 0.387W/(m~2·K).The calculated value agreed with the experimental one.(4)The comparison results of heat transfer for blocks without and with broken bridges showed that:Heat transfer coefficients of block without and with broken bridge were0.647W/(m~2·K)and 0.383W/(m~2·K)by simulation,respectively.The existence of the broken bridge could block heat transfer and achieve the purpose of heat preservation and energy saving.The block adopted a broken bridge structure.The temperature change at the broken bridge significantly accelerated.Broken bridges hindered the transfer of heat flow and increased heat insulation performance.