Preparation And Properties Of Thermal Insulation Protective Composite Made By Foam Concrete-UHPC With Aeolian Sand

The natural environment with large temperature difference and the human military environment such as explosive penetration in Northwest China put forward the requirements of high comfort and strong anti strike for local buildings.The foam concrete and super high performance concrete can be combined into building materials with both thermal insulation and energy absorption effect,which can meet the design requirements of building thermal insulation protection.However,the shortage of river sand further increases the difficulty and cost of construction in Northwest China.Using aeolian sand instead of river sand to prepare concrete has become the key technology to solve the shortage of local construction sand.Taking the three systems of aeolian sand,low bulk density foam concrete,aeolian sand super high performance concrete and two bonded composite materials as the research object,the influence of aeolian sand on the performance,compressive strength,drying shrinkage and pore structure of foam concrete and its improvement measures are studied.Dynamic and static mechanical properties,drying shrinkage and pore structure are studied.The relationship between the thickness of the sandwich layer and the bearing capacity is explored,and the influence of the thickness of the sandwich layer and the composite form on the energy absorption capacity is clarified.The influence of the interface type on the energy absorption and bearing capacity and the influence of the thickness of the sandwich layer on the insulation effect are analyzed through the mechanical and heat transfer models.The conclusions are as follows:(1)The yield stress of foam concrete increases with the increase of sand cement ratio,and the plastic viscosity decreased initially,followed by an increase,but then again decreased.The shear liquefaction effect of aeolian sand on foam becomes more significant with the increase of sand binder ratio.Both silica fume and PP fiber significantly improve the rheological properties of the slurry,while redispersible latex powder improves the plastic viscosity but reduces the yield stress.The amount of aeolian sand is negatively related to the compressive strength and drying shrinkage of the foam concrete.The different improvement materials make up for the loss of performance caused by aeolian sand and optimize the thermal insulation performance.The porosity of aeolian sand decreases and the average pore size increases,but the effect of improving material on pore structure is not significant.(2)The smooth surface and natural gradation of aeolian sand can improve the workability of UHPC and reduce the porosity of matrix.The 90 d drying shrinkage of UHPC is 609 με,The 28 d compressive strength and three-point bending strength of the composite were178.2MPa and 51.4MPa,respectively,and the 90 d mechanical properties did not collapse.UHPC prepared by natural graded aeolian sand has good impact resistance under single impact pressure and increasing impact pressure.(3)Under uniaxial compression and three-point bending tests,the failure limit load and secant modulus of the composite are negatively correlated with the thickness of the sandwich layer,and the critical proportion of the sandwich layer to ensure the synergistic effect of each phase material is 60%-68%.The quasi-static mechanical model shows that the triangular tooth is better than the rectangular tooth,and the larger the tooth size is,the smaller the total failure deformation is.The lower limit of the proportion of the sandwich layer is 71%;For the fully enclosed composite,the larger the thickness of the sandwich layer is,the smaller the peak stress is,and the upper limit of the proportion of the sandwich layer is 51%.Failure morphology and finite element model show that UHPC panel can improve energy absorption effect through cracking.The heat transfer model shows that the thickness of the sandwich layer is conducive to improving the thermal bridge effect of the floor clapboard,and adding foam concrete can effectively improve the thermal insulation performance.