The Study For Physical And Mechanical Properties Of Nano Recycled Thermal Insulation Concrete

Nano recycled aggregate thermal insulation concrete(RATIC)is one new kind of load-bearing concrete.It combines the advantage of resource-saving and energy-saving and reflects the characteristics of low-carbon environment and sustainable development.Utilization of RATIC could realize the cyclic utilization of concrete and make the duration of thermal insulation system same as structure system.What's more,it could decrease the construction cost of recycled aggregate concrete,accordingly,and obviously increase the performance-price ratio.At the meanwhile,it promots the utilization of recycled aggregate concrete feasibly.This new concrete provides the new way for sustainable development of recycled aggregate concrete.The research on RATIC is of great valve in research and potentially propagable.In this paper,a new kind of concrete was proposed and named RATIC,in which recycled coarse aggregate(RCA),glazed hollow beads and nano particles were used.Followed the theories of systems science,the concrete physical and mechanical properties were evaluated and the mechanism of mechanical properties and thermal insulation properties were revealed in this paper.In this study,a series of orthogonal experiments were tested and the optimal mix proportion of RATIC was determined.Then the mechanical properties,microstructure and heat conduction mechanism of RATIC were researched as below:(1)The study on mix proportion optimum design of RATIC.The orthogonal experimental design method was used to study the significance sequence of all influence factors,including RCA,SF,NS and NCC.Range analysis,variance analysis and multiple comparisons were adopted to analyze the influence of four factors.The order of influence of cement replacements on the compressive strength of the concrete was Silica fume>Nano SiO2>Recycled aggregate>Nano CaCO3.Four factors had a little influence on the thermal insulation coefficient of the RATIC in this study.The optimal mix proportion of RATIC was determined after comprehensive analyses of strength,thermal conductivity and utilization of resources.(2)The study on mechanical properties for RATIC.The influences of the RCA replacement percentage on the compressive strength,the split tensile strength,the flexural strength and the elastic modulus of the RATIC were evaluated.The replacement level of recycled aggregate had little impact on compressive strength of RATIC.As increasing the replacement ratio of recycled aggregate,axial compressive strength,the splitting tensile strength,flexural tensile strength and elasticity modulus of RATIC had the declining tendency.The relation between cube compressive strength and tensile strength,and elastic modulus repectively,were established by data fitting.(3)The study on stress-strain curve in axial compression for RATIC.The stess-strain relationships with different RCA replacement percentages of 0%,30%,50%,70%and 100%were established.In addition,the concrete mechanical properties,elastic modulus and stressstrain relationship were evaluated.Five stress-strain curves of RATIC were given for comparisons between different percentages of RCA replacement.As the RCA replacement percentage increased,the values of the ultimate strains had a trend of decreasing and the ?c,u/?c,r-value of RATIC decreased.When the ?c,u/?c,r-value was lower the concrete was more brittle.RATIC with 100%replacement of RCA was more brittle than the NC,the NC was more brittle than the RATIC with various replacement level(30%,50%,70%)of RCA.It was found that some recycled coarse aggregates broke due to the shearing strength.(4)The study on microstructure properities of RATIC.In this paper,the micro-morphologies,hydration outcome composition and porosity of hardened cement paste for RATIC with different RCA replacement percentages were investigated by the Scanning electron microscope(SEM),X-Ray DiffractomerXRD and Mercury Injection.These were observed through SEM that,the gather of mass calcium hydroxide crystal at the interfacial transition zone between natural aggregate and cement mortar;good occlusion between new cement mortar and old cement mortar of recycled coarse aggregate;good bonding between external wall of glazed hollow bead and cement mortar without obvious interface,the internal structure still kept in the physical state of cellular seal holes even the glazed hollow bead was broken.The X-Ray test showed that the addition of silica fume and Nano-SiO2 could strengthen the recycled coarse aggregate,and improve the new interface transition zone between recycled coarse aggregate and cement pastes,and increase the compressive strength of concrete;recycled coarse aggregate impacted the hydration of C2S(C3S)to an extent,C-S-H content showed the rising tendency which is consistent with cube compressive strength.The experiment data of mercury injection test showed that RATIC had the obvious fractal characters.The fractal dimension indicated the characteristic of the pore distribution.The compressive strength of RATIC could be estimated by the macro-pore fractal dimension and the thermal conductivity coefficient of RATIC could be estimated by the average fractal dimension.(5)The study on heat transfer mechanism of RATIC.Based on the theoretical calculations,finite element simulation and experimental data,the thermal conductivity coefficient modal was established,while the pore fractal dimension and solid holes porosity of glazed hollow beads were considered.This paper provides the fundamental basis for the failure mechanism and structural nonlinearity analysis of RATIC and also is premise for the further research on various properties of RATIC.