Study On The Influence Of Hydrotalcite/Carbon Nanotubes On The Performance Of Cement Mortar

Cement-based materials have been sufferring from carbonation corrosion for a long time,resulting in insufficient durability,which seriously affects the performance of cement-based materials.In this paper,starting from the perspective of curing CO₃^2-and blocking the corrosion of external harmful substances,a kind of material named CoFeMgAl-LDHs/MWCNTs composites was prepared and mixed into mortar to study the effects of composite materials on physical properties,mechanical properties and carbonation resistance of cement mortar.CoFeMgAl-LDHs/MWCNTs composite material is a new type of functional material,which has the advantages of hydrotalcite and multi-walled carbon nanotubes,such as interlayer anion exchange function,good mechanical properties,large specific surface area,etc.,which can cure cement-based harmful anions in the material and block its transmission channels,improving the performance of cement-based materials.In this paper,the microstructure,composition and macroscopic stability of CoFeMgAl-LDHs/MWCNTs composite materials are studied by means of XRD,SEM,EDS,BET,Raman,etc.The CoFeMgAl-LDHs/MWCNTs materials were applied to mortar to study its influence on the performance of mortar.The main conclusions are as follows:（1）The CoFeMgAl-LDHs/MWCNTs composites were synthesized by the electrostatic self-assembly method and the mass ratio of the two materials was 1:1;Elemental composition analysis of the material showed that the carbon element of the composite material accounted for about50%,which basically conformed to the material ratio;The composite material has a three-dimensional layered structure that combines the advantages of the two materials.Its specific surface area can reach249.08m²/g,and its stability in aqueous solution is good,which is conducive to its dispersion in cement-based materials.（2）Adding CoFeMgAl-LDHs/MWCNTs composite into mortar has a great influence on the basic working performance of mortar.Due to the strong water absorption of composite materials,when the content is 3%,the mortar completely loses its fluidity,but the water retention of mortar gradually increases,up to 96.5%;The apparent density and mechanical strength of mortar show a trend of first increasing and then decreasing.When the content is 2%,its apparent density,compressive strength and flexural strength are the maximum,respectively 2257.4 kg/m³,47.2 MPa,7.2 MPa,compared with the benchmark group mortar,the mechanical properties have been significantly improved;With the increase of the content of composite materials,the initial surface adsorption（ISA）value of mortar gradually increases,final water absorption（FWA）value has little difference.When the content is 2%,the permeability of mortar is the minimum,which is the optimal content.Comprehensive analysis,2%is the optimal content.（3）The micro-morphology detection analysis of mortar shows that the composite materials have a favorable impact on the performance of mortar mainly through the filling effect of micro-aggregate,the pull-out resistance,the adhesion of hydration products and the bridging effect.However,with the increase of the content,the agglomeration phenomenon of the composite materials is unfavorable to the performance of mortar.（4）Carbonization at an appropriate age will enhance the mechanical properties of the mortar and improve its internal pore structure.However,as the carbonization age increases,the carbonized products gradually accumulate and expand,resulting in the destruction of the internal density of the mortar.In the early stage of carbonization,the carbonization speed of the mortar fast,the carbonization depth and quality change greatly.In the later stage of carbonization,the carbonization depth and quality increase slowly.Among them,the 2%content of mortar has the best carbonization resistance;according to the p H value of the mortar at different depths,different depths of mortar can be distinguished the degree of carbonization is divided into three carbonized zones:fully carbonized zone,partially carbonized zone,and non-carbonized zone.The partial carbonized zone is about twice the depth of the fully carbonized zone.