| As one of textile reinforced cementitious material(TRC),the performance of concrete canvas is influenced by the cement matrix,3D spacer fabric,and the preparation method.It is very necessary to improve the performance of concrete canvas under different environmental conditions due to its extensive applications in the fields of military tents,retaining walls and slope protection,tunnel lining and pipeline protection,etc.This thesis carried ou the studies from the following three aspects:the optimization of cementitious material formula,the effect of fabric geometrical pattern on the mechanical properties of concrete canvas and the durability of concrete canvas.As to the cementitious matrix,in terms of basic requirements of final setting time less than 2h as well as the 28d through-thickness compressive strength greater than 45MPa,two different relative humidity conditions(i.e.RH=60±5%and water immersion)with the fixed curing temeperature(T=20±2?)are used to optimize the recipe of cement matrix of concrete canvas subjected to air-dry and underwater service conditions,respectively.Gypsum modified calcium sulfoaluminate cement or calcium aluminate cements(i.e.Ternal-EP and Fondu)are considered as a solution to optimize the mix proportions of cement matrix based on the through-thickness compressive strength test,QXRD analysis of hydrated cment paste,and the thermodynamic modeling.In addition,both slica fume and calicume dioxide are included to further improve the mechanical performance of concrete canvas if necessary.The optimal mix proportion under air-dry conditions is TP75-HH25A and the optimal mix proportion under underwater service conditions is725CSA80-HH20W,both of which meet the requirements of final setting time less than 2h as well as the28d through-thickness compressive strength greater than 45MPa.Calcium aluminate cement has better mechanical properties under natural curing conditions.Under water-immersion conditions,as the content of gypsum increases,the strength of calcium aluminate cement decreases.Sulfoaluminate cement with low gypsum content cured under water-immersion conditions is more effective than calcium aluminate cment and sulfoaluminate cement cured under air-dry conditions.When gypsum content is greater than 30%,cracking will occur.Under air-dry conditions,the combination of thermodynamic simulation and experiment is better.The content of gypsum when the mechanical properties are optimal is equivalent to the content of gypsum when the solid volume reaches the maximum in the thermodynamic simulation.This explains that thermodynamic simulation can provide guidance for the experiment;Under water-immersion conditions,due to the boundary conditions which are not well controlled,the test results cannot correspond well with the theoretical values,which leads to a poor correspondence between the thermodynamic simulation and the experiment.As to 3D spacer fabrics,the effect of thickness,mesh stitch and type of yarns in mesh layer on the tensile properties of 3D spacer fabrics and thickness on the puncture resistance are researched respectively.The experimental data shows:(1)The thicker the thickness,the worse the tensile properties of 3D spacer fabric and the better puncture resistance;(2)The 3D spacer fabric with rectangular mesh stitch has better tensile properties than lozenge-quadrilateral mesh stitch.With the optimal formula TP75-HH25A under air-dry conditions,the influence of thickness,mesh stitch and type of yarns in mesh layer on the compressive properties,tensile properties,flexural properties and puncture resistance of concrete canbas in the warp and weft direction is studied,and the fabric geometry effect is discussed.When the concrete canvas has the same apparent density,the thickness and the compressive strength are positively correlated,while mesh stitch and type of yarns in mesh layer have little effect on the compressive strength.The thickness of the concrete canvas is negatively correlated with the tensile performance.The tensile performance of the concrete canvas with rectangular mesh stitch is better than lozenge-quadrilateral mesh stitch,which is the same as 3D spacer fabric.When the mesh layer is up,the thicker the concrete canvas,the worse the flexural performance.The optimal 3Dspacer fabric finally screened out is 10-R3*2.5-mul.As to durability performance,10-R3*2.5-mul is selected.In order to provide a reference for the application of concrete canvas in different environments,the volume stability and frost resistance of the concrete canvas are explored.As for the volume stability,the shrinkage in warp of sample with optimal mix proportion TP75-HH25A cured under air-dry condition for 90d reaches 357*10-6,while 398*10-6 in weft.The shrinkage in warp of the other sample with optimal mix proportion 725CSA80-HH20W cured under water-immersion condition for 90d reaches 1081*10-6,while 1124*10-6 in weft.The volume stability in the warp direction is better than the volume stability in the weft direction.It can be seen that the warp spacer yarn has a better effect of restricting deformation than the weft spacer yarn.For the concrete canvas prepared with the mix ratio of TP75-HH25A,it can stand 375 freeze-thaw cycles. |
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